Co-reporter:Xu Zhao;Hong-En Wang;Jian Cao;Wei Cai
Chemical Communications 2017 vol. 53(Issue 77) pp:10723-10726
Publication Date(Web):2017/09/26
DOI:10.1039/C7CC06851D
A carbon-free MoO2 nanosheet with amorphous/crystalline hybrid domain was synthesized, and demonstrated to be an efficient host material for lithium-ion capacitors. Discrepant crystallinity in MoO2 shows unique boundaries, which can improve Li-ion diffusion through the electrode. Improved rate capacities and cycling stability open the door to design of high-performance lithium ion capacitor bridging batteries and supercapacitors.
Co-reporter:Xianfu Meng;Zihang Liu;Bo Cui;Dan Qin;Huiyuan Geng;Wei Cai;Liangwei Fu;Jiaqing He;Zhifeng Ren
Advanced Energy Materials 2017 Volume 7(Issue 13) pp:
Publication Date(Web):2017/07/01
DOI:10.1002/aenm.201602582
Grain or phase boundaries play a critical role in the carrier and phonon transport in bulk thermoelectric materials. Previous investigations about controlling boundaries primarily focused on the reducing grain size or forming nanoinclusions. Herein, liquid phase compaction method is first used to fabricate the Yb-filled CoSb3 with excess Sb content, which shows the typical feature of low-angle grain boundaries with dense dislocation arrays. Seebeck coefficients show a dramatic increase via energy filtering effect through dislocation arrays with little deterioration on the carrier mobility, which significantly enhances the power factor over a broad temperature range with a high room-temperature value around 47 μW cm−2 K−1. Simultaneously, the lattice thermal conductivity could be further suppressed via scattering phonons via dense dislocation scattering. As a result, the highest average figure of merit ZT of ≈1.08 from 300 to 850 K could be realized, comparable to the best reported result of single or triple-filled Skutterudites. This work clearly points out that low-angle grain boundaries fabricated by liquid phase compaction method could concurrently optimize the electrical and thermal transport properties leading to an obvious enhancement of both power factor and ZT.
Co-reporter:Zihang Liu, Yumei Wang, Weihong Gao, Jun Mao, Huiyuan Geng, Jing Shuai, Wei Cai, Jiehe Sui, Zhifeng Ren
Nano Energy 2017 Volume 31() pp:194-200
Publication Date(Web):January 2017
DOI:10.1016/j.nanoen.2016.11.010
•Doping on the Mg site leads to higher mobility and power factor in comparison with doping on Sb sub-lattice, originated from the less introduced perturbation to valence band upon doping.•A peak ZT of ~1.3 at ~550 K and average ZT of ~1.1 between 300 K and 550 K are achieved by Ca doping on the Mg site.P-type nanostructured α-MgAgSb holds a great promise for low temperature waste heat energy harvesting. In this work, we first investigate the effect of doping site on the carrier transport behavior of nanostructured α-MgAgSb. Ca doping on Mg site is rationally chosen to optimize carrier concentration and thus enhance power factor. It is demonstrated that Ca doping on the Mg site leads to higher mobility and power factor in comparison with doping on Sb site, originated from the less introduced perturbation to valence band upon doping. As the result of doping-site effect, a peak ZT of ~1.3 at ~550 K and average ZT of ~1.1 between 300 K and 550 K are achieved by Ca doping on the Mg site. Our current work on only points out that doping on the site that has less influence on the charge-conducting band should be a critical doping principle in thermoelectric materials field, but also highlights the promising prospect of nanostructured α-MgAgSb for low temperature power generation.
Co-reporter:Zihang Liu, Weihong Gao, Xianfu Meng, Xiaobo Li, ... Jiehe Sui
Scripta Materialia 2017 Volume 127(Volume 127) pp:
Publication Date(Web):15 January 2017
DOI:10.1016/j.scriptamat.2016.08.037
Mechanical robustness plays an important role in the manufacturing and assembling processes as well as reliable operation for thermoelectric devices. Herein, we first give a detailed study on the mechanical properties of nanostructured α-MgAgSb. The corresponding Young's modulus, nanoindentation hardness, compressive strength, and fracture toughness are 55.0 GPa, 3.3 GPa, 389.6 MPa, and 1.1 MPa m1/2, respectively, which have a close relationship with the intricate microstructure. Compared with other p-type thermoelectric materials, the good mechanical properties of nanostructured α-MgAgSb further highlight the realistic prospect for power generation.Download high-res image (244KB)Download full-size image
Co-reporter:Zihang Liu, Jun Mao, Shengyuan Peng, Binqiang Zhou, Weihong Gao, Jiehe Sui, Yanzhong Pei, Zhifeng Ren
Materials Today Physics 2017 Volume 2(Volume 2) pp:
Publication Date(Web):1 September 2017
DOI:10.1016/j.mtphys.2017.08.002
•Te doping on the Sb site, as an n-type strong donor, could significantly suppress the high-temperature bipolar effect in the nanostructured Zintl Zr3Ni3Sb4.•Both high majority-carrier concentration and enlarged band gap lead to the significant suppression of high-temperature bipolar effect upon Te doping.•Both carrier mobility and power factor by Te doping, due to the detrimental effect of ionized scattering, are lower than that of Cu doping in which the mixed acoustic phonon and ionized impurity scattering dominates.Thermoelectric figure of merit ZT has been greatly improved in the past decade via band engineering to enhance power factor or nanostructuring to reduce thermal conductivity, but less attention has been paid to other significant factors, e.g., carrier scattering mechanism, bipolar effect, etc. Here we show that Te doping on the Sb site, as an n-type strong donor, could significantly suppress the high-temperature bipolar effect in the nanostructured Zintl Zr3Ni3Sb4, which can be ascribed to the combination of high majority-carrier concentration and enlarged band gap. A relatively good ZT of ∼0.6 at 773 K for Te doping can be achieved and that is almost double of the previous reported ZT by Cu doping. In addition, the role of carrier scattering mechanism on the low-temperature electrical transport properties is also pointed out, where both carrier mobility and power factor of Te doping, due to the detrimental effect of ionized impurity scattering, are lower than that of Cu doping in which the mixed acoustic phonon and ionized impurity scattering dominates.Download full-size image
Co-reporter:Xin Zhang;Jie-He Sui;Yong-Chao Lei;Wei Cai
Acta Metallurgica Sinica (English Letters) 2017 Volume 30( Issue 12) pp:1231-1235
Publication Date(Web):22 June 2017
DOI:10.1007/s40195-017-0606-3
Nanocrystalline Ti54.5Ni45.5 thin film was prepared by magnetron sputtering followed by rapid thermal annealing. The film displayed martensite structure and (001) compound twin substructure, and the transformation temperatures Ms and As are 313 and 365 K, respectively. The reflectivity for the wavelength from 200 to 800 nm at 298 and 393 K was investigated, and the results showed that the optical reflectivity contrast between martensite and austensite at 780, 650, 514 and 405 nm was 105.64, 170.83, 112.22 and 149.92%, respectively, which were larger than those of other reported optical recording materials.
Co-reporter:Zihang Liu;Yumei Wang;Jun Mao;Huiyuan Geng;Jing Shuai;Yuanxu Wang;Ran He;Wei Cai;Zhifeng Ren
Advanced Energy Materials 2016 Volume 6( Issue 7) pp:
Publication Date(Web):
DOI:10.1002/aenm.201502269
Despite the unfavorable band structure with twofold degeneracy at the valence band maximum, MgAgSb is still an excellent p-type thermoelectric material for applications near room temperature. The intrinsically weak electron–phonon coupling, reflected by the low deformation potential Edef ≈ 6.3 eV, plays a crucial role in the relatively high power factor of MgAgSb. More importantly, Li is successfully doped into Mg site to tune the carrier concentration, leading to the resistivity reduction by a factor of 3 and a consequent increase in power factor by ≈30% at 300 K. Low lattice thermal conductivity can be simultaneously achieved by all-scale hierarchical phonon scattering architecture including high density of dislocations and nanoscale stacking faults, nanoinclusions, and multiscale grain boundaries. Collectively, much higher average power factor ≈25 μW cm−1 K−2 with a high average ZT ≈ 1.1 from 300 to 548 K is achieved for 0.01 Li doping, which would result in a high output power density ≈1.56 W cm−2 and leg efficiency ≈9.2% by calculations assuming cold-side temperature Tc = 323 K, hot-side temperature Th = 548 K, and leg length = 2 mm.
Co-reporter:Jing Shuai, Zihang Liu, Hee Seok Kim, Yumei Wang, Jun Mao, Ran He, Jiehe Sui and Zhifeng Ren
Journal of Materials Chemistry A 2016 vol. 4(Issue 11) pp:4312-4320
Publication Date(Web):12 Feb 2016
DOI:10.1039/C6TA00507A
Bi-based Zintl compounds, Ca1−xYbxMg2Bi2 with the structure of CaAl2Si2, have been successfully prepared by mechanical alloying followed by hot pressing. We found that the electrical conductivity, Seebeck coefficient, carrier concentration, and thermal conductivity can be adjusted by changing the Yb concentration. All Ca1−xYbxMg2Bi2 samples have low carrier concentrations (∼2.4 to 7.2 × 1018 cm−3) and high Hall mobility (∼119 to 153 cm2 V−1 s−1) near room temperature. The partial substitution of Ca with Yb causes structural disorders, which lowers the thermal conductivity. The highest figure of merit of ∼1.0 is observed in Ca0.5Yb0.5Mg2Bi2, and ∼0.8 in the unsubstituted CaMg2Bi2 and YbMg2Bi2. A small amount of free Bi was found in all the samples except YbMg2Bi2. By reducing the initial Bi concentration, we succeeded in obtaining phase pure samples in all compositions, which resulted in a much better thermoelectric performance, especially much higher (ZT)eng and a conversion efficiency near 11%. Such a high efficiency makes this material competitive with half-Heuslers and skutterudites.
Co-reporter:Zihang Liu, Jing Shuai, Jun Mao, Yumei Wang, Zhengyun Wang, Wei Cai, Jiehe Sui, Zhifeng Ren
Acta Materialia 2016 Volume 102() pp:17-23
Publication Date(Web):1 January 2016
DOI:10.1016/j.actamat.2015.09.033
Abstract
We report the effect of Sb content in MgAg0.97Sbx (x = 0.99, 0.9925, 0.995, and 1.00) on output power and leg efficiency. Due to the doubling of carrier concentration with increasing the Sb content, power factor is enhanced around 20% over the whole temperature range. Simultaneously, the average thermoelectric figure of merit (ZT) is even enhanced a little in spite of the increased corresponding thermal conductivity. We further calculated the engineering power factor (PF)eng, output power, engineering figure of merit (ZT)eng and leg efficiency by taking into account of the Thomson effect. Assuming Tc = 300 K and Th = 548 K, leg length ∼2 mm, an output power of ∼1.77 W cm−2 and leg efficiency η of ∼10.1% are finally obtained for the optimized composition MgAg0.97Sb0.995.
Co-reporter:Qian Cheng, Hongxuan Guo, Yu Li, Shouxin Liu, Jiehe Sui, Wei Cai
Journal of Colloid and Interface Science 2016 Volume 475() pp:1-7
Publication Date(Web):1 August 2016
DOI:10.1016/j.jcis.2016.04.040
Ultrasmall core-shell Fe3O4@NaYF4:Yb3+/Er3+ nanoparticles with bifunctional properties have been successfully synthesized via one pot thermolysis method using oleylamine as both solvent and stabilizer. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), upconversion (UC) luminescence spectra and the physical properties measurement system (PPMS) were used to characterize the resulting samples. The synthesized samples have uniform morphology with a mean size of 14.5 nm and excellent dispersibility. Moreover, these nanoparticles exhibit superparamagnetic behaviour with saturation magnetization of 8.45 emμ/g and efficient up-conversion emission with a two-photon induced process when excited by a 980 nm laser. These results suggest that the synthesized ultrasmall bifunctional nanoparticles may find many biomedical applications, such as clinical diagnosis and treatment of cancers.Ultrasmall core-shell Fe3O4@NaYF4:Yb3+/Er3+ nanostructure particles with bifunctional properties have been successfully synthesized via one pot thermolysis method using oleylamine as both solvent and stabilizer.
Co-reporter:Jian Yao, Xiaohang Zheng, Wei Cai, Jiehe Sui
Journal of Alloys and Compounds 2016 Volume 661() pp:43-48
Publication Date(Web):15 March 2016
DOI:10.1016/j.jallcom.2015.11.191
•Ni55.2Mn24.7Ga19.9Gd0.2 thin film was deposited by DC magnetron sputtering.•Single phase structure of 7M martensite is formed in the annealed film.•Variants are (202) Ι type twin relationship with clear and straight boundaries.•Stable SME is observed in the annealed thin film above 200 °C.Nanocrystalline Ni55.2Mn24.7Ga19.9Gd0.2 high temperature shape memory thin films had been prepared by the DC magnetron sputtering followed by rapid thermal annealing (RTA). Surface morphology, crystal structure, martensitic transformation behavior and shape memory effect (SME) were systematically investigated. The results showed that as-deposited film displayed a coexistence of amorphous and nanocrystal, while the annealed film was a single phase of seven-layered modulated martensite structure with the grain size about 200–500 nm at room temperature. The annealed film showed one step reversible martensitic transformation with martensitic transformation start temperature of 283 °C. Adjacent lamellar variants exhibited a (202) type Ι twin relationship and well coherent interlamellar interfaces. The annealed Ni55.2Mn24.7Ga19.9Gd0.2 thin film displayed a stable SME above 200 °C, which could be used in high temperature field as micro-electro-mechanical-system (MEMS) devices.
Co-reporter:Jing Shuai, Yumei Wang, Zihang Liu, Hee Seok Kim, Jun Mao, Jiehe Sui, Zhifeng Ren
Nano Energy 2016 Volume 25() pp:136-144
Publication Date(Web):July 2016
DOI:10.1016/j.nanoen.2016.04.023
•Thermoelectric properties of phase pure Zintl compounds Ca1−xYbxZn2Sb2, Ca1−xEuxZn2Sb2, and Eu1−xYbxZn2Sb2 prepared by ball milling method are characterized.•The highest figure of merit of ~0.9 is achieved in Ca0.25Yb0.75Zn2Sb2, ~50% higher than the best reported ZT in similar materials prepared by melting-solidification-annealing method.It has been previously shown that Zintl compounds Ca1−xYbxZn2Sb2 and EuZn2Sb2 could be good candidates as thermoelectric materials. However, the conventional synthesis process via melting-solidification-annealing introduces impurities and vacancies, resulting in abnormal high carrier concentration and ultimately low thermoelectric properties. Here we report the enhanced thermoelectric performance of Ca1−xYbxZn2Sb2 (x=0, 0.25, 0.5, 0.75, and 1) prepared by ball milling and hot pressing. XRD confirms the samples are pure Zintl phase within its limit. Other compounds EuZn2Sb2, Eu0.5Yb0.5Zn2Sb2, and Eu0.5Ca0.5Zn2Sb2 are also prepared by ball milling and hot pressing to further understand them. The observed changes in effective mass appear to be one of the reasons for the big difference of carrier mobility in Ca and rare earth (Yb, Eu) alloyed compounds. The defects caused by alloying are the dominant phonon scattering source in these materials. The highest figure of merit of ~0.9 is achieved in Ca0.25Yb0.75Zn2Sb2, ~50% higher than the best reported ZT in similar materials prepared by melting-solidification-annealing method.Ball milling and hot pressing has been demonstrated to be effective to fabricate phase pure Zintl compounds AZn2Sb2, especially Ca1−xYbxZn2Sb2 with enhanced thermoelectric properties. The highest ZT value achieved is ~0.9 for x=0.75 at 773 K, ~50% higher than the best of the sample made by melting method.
Co-reporter:Jing Shuai;Huiyuan Geng;Yucheng Lan;Zhuan Zhu;Chao Wang;Ching-Wu Chu;Zihang Liu;Jiming Bao;Zhifeng Ren
PNAS 2016 Volume 113 (Issue 29 ) pp:E4125-E4132
Publication Date(Web):2016-07-19
DOI:10.1073/pnas.1608794113
Complex Zintl phases, especially antimony (Sb)-based YbZn0.4Cd1.6Sb2 with figure-of-merit (ZT) of ∼1.2 at 700 K, are good candidates as thermoelectric materials because of their intrinsic “electron–crystal, phonon–glass”
nature. Here, we report the rarely studied p-type bismuth (Bi)-based Zintl phases (Ca,Yb,Eu)Mg2Bi2 with a record thermoelectric performance. Phase-pure EuMg2Bi2 is successfully prepared with suppressed bipolar effect to reach ZT ∼ 1. Further partial substitution of Eu by Ca and Yb enhanced ZT to ∼1.3 for Eu0.2Yb0.2Ca0.6Mg2Bi2 at 873 K. Density-functional theory (DFT) simulation indicates the alloying has no effect on the valence band, but does affect
the conduction band. Such band engineering results in good p-type thermoelectric properties with high carrier mobility. Using
transmission electron microscopy, various types of strains are observed and are believed to be due to atomic mass and size
fluctuations. Point defects, strain, dislocations, and nanostructures jointly contribute to phonon scattering, confirmed by
the semiclassical theoretical calculations based on a modified Debye–Callaway model of lattice thermal conductivity. This
work indicates Bi-based (Ca,Yb,Eu)Mg2Bi2 is better than the Sb-based Zintl phases.
Co-reporter:Zihang Liu, Huiyuan Geng, Jing Shuai, Zhengyun Wang, Jun Mao, Dezhi Wang, Qing Jie, Wei Cai, Jiehe Sui and Zhifeng Ren
Journal of Materials Chemistry A 2015 vol. 3(Issue 40) pp:10442-10450
Publication Date(Web):03 Jul 2015
DOI:10.1039/C5TC01560J
The effect of Ni doping on both electron and phonon transport properties of nanostructured CoSbS has been investigated in this study. We found a more than 2 times increase on figure-of-merit (ZT). The noticeable enhancement is mainly attributed to the optimized carrier concentration, high effective mass and strong electron–phonon scattering upon Ni doping. A ZT of 0.5 was achieved at 873 K together with a power factor of 20 μW cm−1 K−2 for the Ni doped CoSbS samples. The reduced lattice thermal conductivity via the strong electron–phonon scattering for Ni doped CoSbS samples is confirmed by the quantitative calculation of the various phonon scattering mechanisms according to the Callaway model.
Co-reporter:Zihang Liu, Jing Shuai, Huiyuan Geng, Jun Mao, Yan Feng, Xu Zhao, Xianfu Meng, Ran He, Wei Cai, and Jiehe Sui
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 41) pp:23047
Publication Date(Web):October 5, 2015
DOI:10.1021/acsami.5b06492
Microstructure has a critical influence on the mechanical and functional properties. For thermoelectric materials, deep understanding of the relationship of microstructure and thermoelectric properties will enable the rational optimization of the ZT value and efficiency. Herein, taking AgSbSe2 as an example, we first report a different role of alkaline-earth metal ions (Mg2+ and Ba2+) doping in the microstructure and thermoelectric properties of p-type AgSbSe2. For Mg doping, it monotonously increases the carrier concentration and then reduces the electrical resistivity, leading to a substantially enhanced power factor in comparison to those of other dopant elements (Bi3+, Pb2+, Zn2+, Na+, and Cd2+) in the AgSbSe2 system. Meanwhile, the lattice thermal conductivity is gradually suppressed by point defects scattering. In contrast, the electrical resistivity first decreases and then slightly rises with the increased Ba-doping concentrations due to the presence of BaSe3 nanoprecipitates, exhibiting a different variation tendency compared with the corresponding Mg-doped samples. More significantly, the total thermal conductivity is obviously reduced with the increased Ba-doping concentrations partially because of the strong scattering of medium and long wavelength phonons via the nanoprecipitates, consistent with the theoretical calculation and analysis. Collectively, ZT value ∼1 at 673 K and calculated leg efficiency ∼8.5% with Tc = 300 K and Th = 673 K are obtained for both AgSb0.98Mg0.02Se2 and AgSb0.98Ba0.02Se2 samples.Keywords: AgSbSe2; alkaline-earth metal ions (M2+) doping; leg efficiency; microstructure; nanoprecipitates; thermoelectric properties
Co-reporter:Jing Shuai, Yumei Wang, Hee Seok Kim, Zihang Liu, Jingying Sun, Shuo Chen, Jiehe Sui, Zhifeng Ren
Acta Materialia 2015 Volume 93() pp:187-193
Publication Date(Web):July 2015
DOI:10.1016/j.actamat.2015.04.023
Abstract
Mg3−xNaxSb2 has been prepared successfully by mechanical alloying plus hot pressing to investigate the effects of Na doping on the thermoelectric properties. Thermoelectric properties were characterized by the Seebeck coefficient, electrical resistivity, thermal conductivity, and thermoelectric figure of merit (ZT) from 298 to 773 K. Transport measurements reveal that an optimum doping of 1.25 at.% Na on Mg achieved ZT of 0.6 at 773 K. The enhancement in ZT is attributed to increased carrier concentration and power factor. The low cost, abundance, and nontoxicity makes this material a potentially promising thermoelectric material for power generation at a heat source below 773 K.
Co-reporter:Xianfu Meng, Wei Cai, Zihang Liu, Jing Li, Huiyuan Geng, Jiehe Sui
Acta Materialia 2015 Volume 98() pp:405-415
Publication Date(Web):1 October 2015
DOI:10.1016/j.actamat.2015.07.027
Abstract
Here we demonstrate that the coherency strain fields arising from spinodal decomposition can improve simultaneously the electronic density of states (DOS) near the Fermi level and the phonon-scattering rate in p-type filled skutterudites. Spinodal decomposition is appeared in the p-type filled skutterudite La0.8Ti0.1Ga0.1Fe3CoSb12, which is produced by a combination of water-quenching, long-term annealing and hot-pressing approaches. Within each grain of the hot-pressed sample, there are La-poor and La-rich skutterudite phases. The size of each phase is then substantially reduced to about 200 nm by using rapid solidification of melting–spinning followed by hot-pressing method. Therefore, the coherency strain fields resulted from spinodal decomposition is significantly increased. High resolution transmission electron microscopy (HRTEM) reveals that most of these domains are in the state of tensile. Compared to the quenched sample, the Seebeck coefficient increases about 10% and the lattice thermal conductivity of the optimization sample is reduced about 30% at 700 K. Our theoretical analysis shows that grain boundary scattering has limited contribution to the reduction of lattice thermal conductivity in p-type filled skutterudites. The drastic reduction in the lattice thermal conductivity is mainly caused by phonon scattering through the coherency strain fields. As a result, a peak ZT of about 1.2 at 700 K is obtained in the spun sample. In addition, the spun sample displays good repeatable and stable characteristics.
Co-reporter:Songting Cai, Zihang Liu, Jianyong Sun, Rui Li, Weidong Fei and Jiehe Sui
Dalton Transactions 2015 vol. 44(Issue 3) pp:1046-1051
Publication Date(Web):05 Nov 2014
DOI:10.1039/C4DT03059A
AgSbSe2 possesses extremely low thermal conductivity and high Seebeck coefficient, but the low electronic conductivity leads to a low ZT value. In this paper, Na is used to substitute Sb to improve the electronic conductivity. The results show that Na doping not only improves the power factor caused by the enhanced carrier concentration, but also decreases the thermal conductivity due to point defects, nanoscale stacking faults and Na-rich precipitate. Consequently, a high ZT value of 0.92 is achieved in the AgSb0.99Na0.01Se2 sample.
Co-reporter:Jing Li, Li-Dong Zhao, Jiehe Sui, David Berardan, Wei Cai and Nita Dragoe
Dalton Transactions 2015 vol. 44(Issue 5) pp:2285-2293
Publication Date(Web):11 Dec 2014
DOI:10.1039/C4DT03556A
In the past few years, many studies have been devoted to the thermoelectric properties of copper selenides and sulfides, and several families of materials have been developed with promising performances. In this paper, we report on the synthesis and thermoelectric properties of Na-doped BaCu2Se2 from 20 K to 773 K. By Na doping at the Ba site, the electrical conductivity can be increased by 2 orders of magnitude, and the power factor can reach 8.2 μW cm−1 K−2 at 773 K. Combined with a low thermal conductivity of 0.65 W m−1 K−1, a ZT of 1.0 has been obtained for Ba0.925Na0.075Cu2Se2 at 773 K, which is the highest value reported in this family to date. However, BaCu2Se2 volatilizes at 473 K, so a protective coating is necessary for its application. Besides, we studied the thermal expansion coefficient of BaCu2Se2 in this paper.
Co-reporter:Jing Shuai, Hee Seok Kim, Yucheng Lan, Shuo Chen, Yuan Liu, Huaizhou Zhao, Jiehe Sui, Zhifeng Ren
Nano Energy 2015 Volume 11() pp:640-646
Publication Date(Web):January 2015
DOI:10.1016/j.nanoen.2014.11.027
MgAg0.97Sb0.99 was found to be potentially a new class of thermoelectric materials with ZT values above 1 in the temperature from 100 to 300 °C. In this report, we systematically studied the effect of Na doping in Mg, Mg1−xNaxAg0.97Sb0.99, on the thermoelectric properties and found Na was effective to increase the carrier concentration and power factor, especially below 180 °C, which led to higher ZT values, a better self-compatibility factor, and ultimately a higher output power at the optimal Na concentration of x=0.005–0.0075.Na doping in Mg site of the samples Mg1−xNaxAg0.97Sb0.99 effectively enhances the power factor by increasing carrier concentration. The ZT value was improved from 1.2 at 250 °C for MgAg0.97Sb0.99 sample to 1.26 at 250 °C for Mg0.925Na0.075Ag0.97Sb0.99 sample. High power factor results in higher output power, which is good for fabricating thermoelectric devices.
Co-reporter:Zihang Liu, Yanling Pei, Huiyuan Geng, Jingchao Zhou, Xianfu Meng, Wei Cai, Weishu Liu, Jiehe Sui
Nano Energy 2015 Volume 13() pp:554-562
Publication Date(Web):April 2015
DOI:10.1016/j.nanoen.2015.03.036
•Point defects, including Br substitution on S sites and the intercalated Cu with the Bi2S3 layers, and the increased interfaces between Cu nanoprecipitates and Bi2S3 matrix can significantly suppress the lattice thermal conductivity.•A high ZT=0.72 is obtained for the 0.5 mol% CuBr2 doped Bi2S3 sample at 773 K, which is nearly 800% higher than that of the pristine Bi2S3.Bi2S3 thermoelectric materials have received extensive interests due to the ultrahigh abundance of sulfur element in the Earth׳s crust. However, the high electrical resistivity of pristine Bi2S3 leads to a low ZT value. In this work, incorporating small amounts of CuBr2 into Bi2S3 system prepared by melting and spark plasma sintering can remarkably enhance the thermoelectric performance. Cu intercalation and Br substitution at sulfur sites contribute to a sharp decrease of electrical resistivity. Simultaneously, the strong point defects caused by Br alloying and formed Cu nanoparticles noticeably suppress the thermal conductivity. Collectively, the maximum ZT of 0.72 at 773 K is obtained for the 0.5 mol% CuBr2 doped sample parallel to the press direction, which is the highest ZT value ever reported for Bi2S3 system, even comparable to the PbS-based thermoelectric materials.In our work, CuBr2 doping could remarkably enhance the thermoelectric performance of Bi2S3. Cu intercalation and Br substitution at sulfur sites contribute to a sharp decrease of electrical resistivity. Simultaneously, the strong point defects caused by Br alloying and formed Cu nanoparticles noticeably suppress the thermal conductivity. Collectively, the maximum ZT of 0.72 at 773 K and average ZT of 0.40 from 300 K to 773 K is obtained for the 0.5 mol% CuBr2 doped sample, making it a very robust candidate among the thermoelectric sulfides in the medium temperature range.
Co-reporter:Xin Zhang, Jiehe Sui, Wei Cai, Qingsuo Liu, Ailian Liu
Intermetallics 2015 Volume 67() pp:52-55
Publication Date(Web):December 2015
DOI:10.1016/j.intermet.2015.07.017
Co-reporter:Jing Li, Jiehe Sui, Yanling Pei, Xianfu Meng, David Berardan, Nita Dragoe, Wei Cai and Li-Dong Zhao
Journal of Materials Chemistry A 2014 vol. 2(Issue 14) pp:4903-4906
Publication Date(Web):03 Mar 2014
DOI:10.1039/C3TA14532H
The thermoelectric properties of the Bi1−xNaxCuSeO (0.0 ≤ x ≤ 0.02) system have been investigated in the temperature range 300–923 K. Na doping significantly increased the carrier concentration to ∼0.92 × 1020 cm−3 at the doping amount of x = 0.02. Furthermore, a relatively high carrier mobility and a slight Seebeck coefficient enhancement was seen, thus resulting in a high power factor of 8.0 μW cm−1 K−2 at room temperature. Coupled with a low thermal conductivity reduced by point defects scattering, this leads to a ZT of 0.91 at 923 K for Bi0.985Na0.015CuSeO which is nearly twice the value observed in pristine BiCuSeO.
Co-reporter:Xin Zhang, Jiehe Sui, Zheyi Yang, Xiaohang Zheng, Wei Cai
Materials Letters 2014 Volume 123() pp:250-253
Publication Date(Web):15 May 2014
DOI:10.1016/j.matlet.2014.02.088
Co-reporter:Xin Zhang, Jiehe Sui, Xiaohang Zheng, Zheyi Yang, Wei Cai
Materials Science and Engineering: A 2014 Volume 597() pp:178-182
Publication Date(Web):12 March 2014
DOI:10.1016/j.msea.2013.12.081
The influence of Gd content on the properties of Ni54Mn25Ga21−xGdx alloy was investigated. Proper Gd doping significantly enhanced the mechanical properties. Complete recovery was observed in Ni54Mn25Ga20.9Gd0.1 alloy after heating when the pre-strain is less than 10%, while further doping decreased such properties due to the Gd-rich phase formation.
Co-reporter:Yanling Pei, David Berardan, Nita Dragoe, Celine Barreteau, Jiehe Sui, Li-Dong Zhao
Journal of Alloys and Compounds 2013 Volume 563() pp:261-263
Publication Date(Web):25 June 2013
DOI:10.1016/j.jallcom.2013.02.104
LaFe1-xZnxAsO0.85F0.15 composites were synthesized by solid state reaction in order to improve the mechanical properties while trying to keep the superconductivity. XRD results indicate that LaFe1-xZnxAsO0.85F0.15 are series of superconducting composites composed of LaFeAsO0.85F0.15 and LaZnAsO0.85F0.15. LaFe1-xZnxAsO0.85F0.15 still exhibits superconductivity up to Zn fraction as high as 80%. The critical temperature Tc slightly decreases from 26.2 K for LaFeAsO0.85F0.15 to 23.9 K for LaFe0.2Zn0.8AsO0.85F0.15, which means that the superconductivity can be maintained if 20% of the superconducting phase exists in the composite. In addition, the mechanical properties of LaFe1-xZnxAsO0.85F0.15 including micro-hardness, Young’s modulus and fracture toughness have been significantly improved in the composite as compared to the Zn free sample. Therefore, we conclude the mechanical properties of the LaFeAsO system, and by extension of other systems, can be enhanced by introducing a second phase without deteriorating the superconductivity.Highlights► LaFeAsO0.85F0.15 is superconductor, but LaZnAsO0.85F0.15 is not superconductor. ► LaFe1−xZnxAsO0.85F0.15 are series of superconducting composites composed of LaFeAsO0.85F0.15 and LaZnAsO0.85F0.15. ► The LaFe1−xZnxAsO0.85F0.15 composites exhibit a superconductivity transport signal as the Zn fractions rised up to 80%. ► The mechanical properties of LaFe1−xZnxAsO0.85F0.15 have been significantly improved in the composite as compared to the Zn free sample.
Co-reporter:Yan-Ling Pei, Chaolei Zhang, Jing Li, Jiehe Sui
Journal of Alloys and Compounds 2013 Volume 566() pp:50-53
Publication Date(Web):25 July 2013
DOI:10.1016/j.jallcom.2013.03.037
•Electrical and thermal properties of AgIn5Te8 are anisotropic.•AgIn5Te8 owns intrinsically low thermal conductivity.•Thermal conductivity of AgIn5Te8 shows phonon dominant conduction behavior.•AgIn5Te8 is promising for thermoelectric applications.AgIn5Te8 was synthesized by melting reaction method, the electrical and thermal transport properties have been evaluated along the directions parallel and perpendicular to the ingot growth direction. Both electrical and thermal transport properties show the anisotropic characteristics. The electrical and thermal conductivities along the perpendicular direction are higher than that of parallel one. The large band gap of about 1.0 eV determines a low electrical conductivity. The T−1 dependence of diffusivity for AgIn5Te8 suggests a phonon dominant transport behavior, consistent with the insulating character of the electrical transport properties. AgIn5Te8 owns intrinsically low thermal conductivity, which decreases with increasing temperature, from 1.1 W m−1 K−1 and 0.95 W m−1 K−1 at room temperature to 0.5 W m−1 K−1 and 0.4 W m−1 K−1 at 873 K for AgIn5Te8 along perpendicular and parallel directions, respectively. This low thermal conductivity for AgIn5Te8 demonstrates this system could be promising for thermoelectric applications by improving electrical transport properties through tuning carrier concentrations.
Co-reporter:Jiehe Sui, Jing Li, Shujie Yang, Zhiguo Li, Wei Cai
Materials Letters 2013 100() pp: 32-35
Publication Date(Web):
DOI:10.1016/j.matlet.2013.02.098
Co-reporter:Qian Cheng, Jiehe Sui and Wei Cai
Nanoscale 2012 vol. 4(Issue 3) pp:779-784
Publication Date(Web):12 Dec 2011
DOI:10.1039/C1NR11365H
β-NaGdF4:Yb3+/Er3+ nanoparticles (NPs) codoped with Li+ ions were prepared for the first time via a thermal decomposition reaction of trifluoroacetates in oleylamine. The influence of site occupancy of Li+ on the upconversion emission of β-NaGdF4:Yb3+/Er3+ NPs was investigated in detail. The upconversion emission intensity was significantly enhanced by introducing different concentrations of Li+ ions. In contrast to lithium-free β-NaGdF4:Yb3+/Er3+, the green and red UC emission intensities of the NPs codoped with 7 mol% Li+ ions were enhanced by about 47 and 23 times, respectively. The luminescence enhancement should be attributed to the distortion of the local asymmetry around Er3+ ions. The mechanisms for the enhancement of upconversion emission were discussed. In addition, it was found in our research work that β-NaGdF4:Yb3+/Er3+ NPs exhibited paramagnetic features at room temperature and the magnetization was slightly increased by introducing Li+ ions.
Co-reporter:Jiehe Sui, Cheng Zhang, Da Hong, Jing Li, Qian Cheng, Zhiguo Li and Wei Cai
Journal of Materials Chemistry A 2012 vol. 22(Issue 27) pp:13674-13681
Publication Date(Web):18 May 2012
DOI:10.1039/C2JM31905E
Monodisperse ZnFe2O4 nanoparticles with sizes less than 10 nm have been successfully assembled on multi-walled carbon nanotubes (MWCNTs) by in situ high-temperature decomposition of the precursor iron(III) acetylacetonate, zinc acetate and MWCNTs in polyol solution. A possible formation mechanism was proposed, which suggests that the ZnFe2O4 nanoparticles are formed on the surface of MWCNTs through an aggregation thermochemical reaction process between ZnO and γ-Fe2O3 subparticles. It was found that the coverage density on the MWCNTs could be easily controlled by changing the concentration of the precursor. As anode materials for Li-ion batteries, the MWCNT–ZnFe2O4 nanocomposites showed high rate capability and superior cycling stability with a specific capacity of 1152 mA h g−1, which was much higher than that of ZnFe2O4 nanoparticles. The MWCNTs served as good electron conductors and volume buffers in improving the lithium performance of MWCNT–ZnFe2O4 nanocomposites during the discharge–charge process. Magnetic measurements showed that the MWCNT–ZnFe2O4 nanocomposites are superparamagnetic at room temperature and the magnetization of the samples can be controlled by the reaction conditions. The as-synthesized MWCNT–ZnFe2O4 nanocomposites are water dispersible and can be manipulated by an external magnetic field. Therefore, the nanocomposites have significant potential for application in the fields of energy storage, composites, wastewater treatment and biomaterials.
Co-reporter:X.H. Tian, J.H. Sui, X. Zhang, X.H. Zheng, W. Cai
Journal of Alloys and Compounds 2012 Volume 514() pp:210-213
Publication Date(Web):15 February 2012
DOI:10.1016/j.jallcom.2011.11.077
The sintered Ni–Mn–Ga alloys with various grain sizes have been fabricated by using the spark plasma sintering method. The effect of grain size on martensitic transformation, mechanical and magnetic properties of Ni–Mn–Ga alloys have been investigated for the first time. The results show that martensitic transformation and transformation hysteresis are significantly affected by the grain size. All as-sintered Ni–Mn–Ga alloys exhibit high saturation magnetization despite their different grain sizes. Moreover, it is found that the grain size plays important roles on mechanical properties. The sintered specimen with appropriate grain size exhibits the highest fracture strain reported so far.Highlights► Ni–Mn–Ga shape memory alloys with various grain sizes have been fabricated by the spark plasma sintering technique. ► The effect of grain size on martensitic transformation, mechanical and magnetic properties has been studied for the first time. ► Martensitic transformation and transformation hysteresis are significantly affected by the grain size. ► The highest fracture strain of 29% up to now has been reported in the sintered specimen with appropriate grain size.
Co-reporter:Jiehe Sui, Jing Li, Zhiguo Li, Wei Cai
Materials Chemistry and Physics 2012 Volume 134(Issue 1) pp:229-234
Publication Date(Web):15 May 2012
DOI:10.1016/j.matchemphys.2012.02.057
One dimensional bifunctional magnetic-photocatalytic CNTs/Fe3O4–ZnO nanohybrids were synthesized by one-pot polyol sequential process. The as synthesized products were characterized by X-ray diffraction, Fourier transform infrared spectrometer, transmission electronic microscope, energy dispersive spectrometer, physical properties measurement system and UV–Vis absorption spectroscopy. The results exhibit the ZnO forms heterogenerously on the surface of CNTs/Fe3O4 and the nanohybrids display superparamagnetic behavior at room temperature. Photocatalytic studies verify the as-prepared sample have high photocatalytic activity toward the photodegradation of methyl orange in solution. In addition, the photocatalyst can be recycled using magnetic field and maintain high photocatalytic activity.Highlights► Bifunctional CNTs/Fe3O4–ZnO nanohybrids are synthesized by one-pot polyol process. ► The nanohybrids display superparamagnetic behavior. ► The nanohybrids display high photocatalytic activity under UV-light irradiation. ► The nanohybrids are recycled magnetically and maintain high photocatalytic activity.
Co-reporter:Jiehe Sui, Cheng Zhang, Jing Li, Zhiliang Yu, Wei Cai
Materials Letters 2012 Volume 75() pp:158-160
Publication Date(Web):15 May 2012
DOI:10.1016/j.matlet.2012.02.007
Cobalt nanoparticles (Co NPs) have been successfully synthesized on the surface of carbon nanotubes (CNTs) by in situ high-temperature decomposition of cobalt(III) acetylacetonate and CNTs in polyol solution. It is found that the structure of the Co NPs among the CNTs/Co nanocomposites is the mixture of cubic and hexagnonal phase and the nanocomposites are ferromagnetic. Microwave absorption of the CNTs/Co nanocomposites is higher than that of pure Co NPs and pure CNTs. The catalytic activity for ammonium perchlorate (AP) of CNTs/Co nanocomposites is higher than that of pure Co NPs. The mechanism on the improvement of microwave absorption and catalytic activity of CNTs/Co nanocomposites is discussed briefly.Highlights► CNTs/Co nanohybrids were synthesized by the polyol method. ► Microwave absorption of the CNTs/Co nanohybrids is higher than that of Co NPs and CNTs. ► The catalytic activity of CNTs/Co nanohybrids is higher than that of Co NPs. ► The mechanism on the improvement of microwave absorption and catalytic activity is discussed.
Co-reporter:Jiehe Sui, Xin Zhang, Li Gao, Wei Cai
Journal of Alloys and Compounds 2011 Volume 509(Issue 35) pp:8692-8699
Publication Date(Web):1 September 2011
DOI:10.1016/j.jallcom.2011.06.013
Influence of rare earth Y addition on the microstructure and phase transitions and mechanical properties of polycrystalline Ni50Mn29Ga21 ferromagnetic-shape memory alloy (FSMA) are investigated. It is shown that microstructure of the Ni–Mn–Ga–Y alloys consists of the matrix and the Y-rich phase. The Y-rich phase firstly disperses homogeneously in the matrix with small amounts and then tends to segregate at the grain boundaries with increasing Y substitution for Ga. The Y-rich phase is indexed to Y(Ni,Mn)4Ga phase with a hexagonal CaCu5 type structure. The structural transition from 5 M to 7 M, and then to non-modulated T martensite appears with the increase of Y content. The martensitic transformation temperature increases remarkably with increasing Y content, whereas the Curie temperature almost keeps unchanged. It is revealed that the appropriate addition of Y significantly enhances the yield strength and improves the ductility of the alloys. The mechanism on the influence of Y content on the improved mechanical properties and martensitic transformation temperature is also discussed.Highlights• We report the influence of rare earth Y addition on the microstructure and phase transitions and mechanical properties of polycrystalline Ni50Mn29Ga21 alloy. • The Y-rich phase is indexed to Y(Ni,Mn)4Ga phase with a hexagonal CaCu5 type structure. • The structural transition from 5 M to 7 M, and then to non-modulated T martensite with the increase of Y content. • The martensitic transformation temperature increases remarkably with increasing Y content. • The approximate addition of Y significantly enhances the yeild strength and ductility of the alloys.
Co-reporter:Maryam Amirian;Ali Nabipour Chakoli ;Wei Cai
Journal of Applied Polymer Science 2011 Volume 122( Issue 5) pp:
Publication Date(Web):
DOI:10.1002/app.34317
Abstract
In this research, poly(L-lactide-co-ε-caprolactone) (PLACL) reinforced with well-dispersed multiwalled carbon nanotubes (MWCNTs) nanocomposites were prepared by oxidization and functionalization of the MWCNT surfaces using oligomeric L-lactide (LA) and ε-caprolactone (CL). It is found that the surface functionalization can effectively improve the dispersion and adhesion of MWCNTs in PLACL. The surface functionalization will have a significant effect on the physical, thermomechanical, and degradation properties of MWCNT/PLACL composites. The tensile modulus, yield stress, tensile strength, and elongation at break of composite increased 49%, 60%, 70%, and 94%, respectively, when the concentration of functionalized MWCNTs in composite is 2 wt %. The in vitro degradation rate of nanocomposites in phosphate buffer solution increased about 100%. The glass transition temperature (Tg) of composites was decreased when the concentration of functionalized MWCNTs is 0.5 wt %. With further increasing the concentration of functionalized MWCNTs, the Tg was increased. The degradation kinetics of nanocomposites can be engineered and functionalized by varying the contents of pristine or functionalized MWCNTs. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Co-reporter:Zhiguo Li, Jiehe Sui, Xiaoli Li, and Wei Cai
Langmuir 2011 Volume 27(Issue 6) pp:2258-2264
Publication Date(Web):February 1, 2011
DOI:10.1021/la1043552
Quantum-sized CdS nanorods were synthesized by direct thermal decomposition of a single-source precursor in a monosurfactant system. The CdS nanorods were uniform, had high crystallinity, and exhibited strong quantum confinement effect. The nanorod growth was controlled by an oriented attachment mechanism, and the morphology was determined by the competition between dipole attraction and steric repulsion of nanodots. Increasing precursor concentration and prolonging reaction time were favorable for the formation of CdS nanorods.
Co-reporter:J.H. Sui, Z.Y. Gao, Y.F. Li, Z.G. Zhang, W. Cai
Materials Science and Engineering: A 2009 Volume 508(1–2) pp:33-36
Publication Date(Web):20 May 2009
DOI:10.1016/j.msea.2009.01.018
The influence of Co on the microstructure, phase transformation temperature, mechanical properties and shape memory effect of TiNiNb alloys has been investigated by X-ray diffraction, differential scanning calorimetry, tensile stress–strain measurements and bending tests, respectively. The results show that the addition of Co suppresses the brittle (Ti,Nb)2Ni phase of NiTiNb alloys, and the phase transformation temperature and lattice parameter of Ni46.5−xTi44.5Nb9Cox alloys are decreased with the increase of Co content. The yield strength of NiTiNb alloys has been improved due to the addition of Co. In particular, Ni45.5Ti44.5Nb9Co1 alloy exhibits highest yield strength among the Ni46.5−xTi44.5Nb9Cox (Co = 0.5, 1, 1.5, 2) alloys, and a maximum completely recoverable strain of 7.8% has been achieved.
Co-reporter:Jiehe Sui, Zhiyou Gao, Huiru Yu, Zhiguo Zhang, Wei Cai
Scripta Materialia 2008 Volume 59(Issue 8) pp:874-877
Publication Date(Web):October 2008
DOI:10.1016/j.scriptamat.2008.06.036
A phenomenon whereby both the martensitic transformation start temperature (Ms) and Curie temperature (Tc) of Ni56Fe17Ga27−xCox alloys increase while maintaining Tc > Af > Ms > 100 °C (where Af is the austenite finish temperature) with increasing Co content at the expense of Ga is reported. The martensitic structure of this alloy is 6 M, which is different from the common structure such as 7 and 5 M. The mechanical properties of the Ni56Fe17Ga27−xCox alloys are improved with increasing Co content.
Co-reporter:J.H. Sui, Z.Y. Gao, W. Cai, Z.G. Zhang
Materials Science and Engineering: A 2007 Volumes 454–455() pp:472-476
Publication Date(Web):25 April 2007
DOI:10.1016/j.msea.2006.11.133
Diamond-like carbon films with different bias voltages were deposited on polished NiTi alloys by plasma immersion ion implantation and deposition (PIIID) using acetylene as precursor. The chemical structure of the DLC films was characterized by Raman scattering spectroscopy. The electrochemical behavior and blood compatibility of the DLC coated and uncoated NiTi alloys were investigated by means of potentiodynamic polarization tests, clotting time measurement, and platelets adhesion.The results show the corrosion resistance and blood compatibility of the NiTi alloys is improved due to the DLC films, and the sp3/sp2 ratio and the corrosion resistance of the DLC films on the NiTi alloys first increases and then decreases with the increase of the bias voltage. Thus, it can be inferred that the corrosion resistance of the DLC films is influenced by the sp3/sp2 ratio.
Co-reporter:Jiehe Sui, Wei Cai, Liancheng Zhao
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 2006 Volume 248(Issue 1) pp:67-70
Publication Date(Web):July 2006
DOI:10.1016/j.nimb.2006.04.054
DLC films with various bias voltages were deposited on polished NiTi alloys by plasma immersion ion implantation and deposition (PIIID) using graphite as plasma precursor. Microstructure and nano-hardness of the DLC films were characterized by Raman spectroscopy and nano-indentation system, respectively. The electrochemical corrosion behavior of DLC coated and uncoated NiTi alloys is investigated in Hank’s solution by means of potentiodynamic polarization tests. The results show that on the one hand the corrosion resistance and surface hardness and elastic modulus of the NiTi alloys are remarkably improved due to the deposition of the DLC films, and on the other hand the sp3/sp2 ratio inferred from Raman spectra, hardness, elastic modulus and the corrosion resistance of the DLC films on the NiTi alloys first increase and then decrease with the increase of the bias voltage. It can be concluded that the corrosion resistance of the DLC films is influenced by their microstructure.
Co-reporter:Jingchao Zhou, Lihong Huang, Zhengyun Wang, Zihang Liu, Wei Cai, Jiehe Sui
Journal of Materiomics (December 2016) Volume 2(Issue 4) pp:
Publication Date(Web):December 2016
DOI:10.1016/j.jmat.2016.08.003
ZnSb as a kind of material with abundant resource and low cost has a low thermal conductivity and a high Seebeck coefficient, giving the potential of high thermoelectric properties. In this paper, Cd isoelectronic substitution was adopted to further improve the thermoelectric performance by reducing the lattice thermal conductivity of ZnSb. The results show that Cd substitution reduces the lattice thermal conductivity and increases the electrical conductivity. A high ZT value of 1.22 is achieved at 350 °C for Zn0.915Na0.005Cd0.08Sb.The Cd isoelectrically substituted Na0.005Na0.995Sb samples were prepared by ball milling and hot press. The total thermal conductivity of Na0.005Na0.995Sb was decreased by Cd isoelectronic substitution caused by the mass and size fluctuation between Zn2+ and Cd2+. A high ZT value of 1.22 was obtained at 350 °C for Zn0.915Na0.005Cd0.08Sb sample, which was greater than that of other ZnSb based thermoelectric materials.Figure optionsDownload full-size imageDownload as PowerPoint slide
Co-reporter:Zihang Liu, Yongsheng Zhang, Jun Mao, Weihong Gao, Yumei Wang, Jing Shuai, Wei Cai, Jiehe Sui, Zhifeng Ren
Acta Materialia (15 April 2017) Volume 128() pp:
Publication Date(Web):15 April 2017
DOI:10.1016/j.actamat.2017.02.015
An in-depth understanding of the origin of low lattice thermal conductivity κlat is considered to be the prerequisite for developing and designing high thermoelectric performance materials. However, the microscopic mechanism of low κlat for α-MgAgSb has not been fully elaborated. Here we first thoroughly unveil the underlying mechanism using density functional theory (DFT) calculations. It is demonstrated that the unique lattice dynamic properties of α-MgAgSb contribute to the low κlat, including a large number of optical branches, weak chemical bonding, the strong anharmonic coupling between longitudinal acoustic (LA) and longitudinal optical (LO) branches, high anharmonic behavior of LO branch. Nanostructuring has an effect in decreasing the lattice thermal conductivity due to the high density of boundaries and defects. Most importantly, Yb doping on the Mg site is chosen to optimize carrier concentration and simultaneously create strong point-defect phonon scattering. Collectively, a peak ZT ∼1.4 at 550 K and average ZT ∼1.2 from 300 K to 550 K have been achieved, which further demonstrates the realistic prospect of MgAgSb based thermoelectric materials for low-temperature waste heat harvesting.The microscopic origin of intrinsically low κlat of α-MgAgSb in the lattice dynamics was thoroughly revealed using density functional theory (DFT) calculations. More importantly, we achieve a peak ZT ∼1.4 and average ZT ∼1.2 via Yb doping.
Co-reporter:Jing Li, Jiehe Sui, Yanling Pei, Xianfu Meng, David Berardan, Nita Dragoe, Wei Cai and Li-Dong Zhao
Journal of Materials Chemistry A 2014 - vol. 2(Issue 14) pp:NaN4906-4906
Publication Date(Web):2014/03/03
DOI:10.1039/C3TA14532H
The thermoelectric properties of the Bi1−xNaxCuSeO (0.0 ≤ x ≤ 0.02) system have been investigated in the temperature range 300–923 K. Na doping significantly increased the carrier concentration to ∼0.92 × 1020 cm−3 at the doping amount of x = 0.02. Furthermore, a relatively high carrier mobility and a slight Seebeck coefficient enhancement was seen, thus resulting in a high power factor of 8.0 μW cm−1 K−2 at room temperature. Coupled with a low thermal conductivity reduced by point defects scattering, this leads to a ZT of 0.91 at 923 K for Bi0.985Na0.015CuSeO which is nearly twice the value observed in pristine BiCuSeO.
Co-reporter:Zihang Liu, Huiyuan Geng, Jun Mao, Jing Shuai, Ran He, Chao Wang, Wei Cai, Jiehe Sui and Zhifeng Ren
Journal of Materials Chemistry A 2016 - vol. 4(Issue 43) pp:NaN16840-16840
Publication Date(Web):2016/09/28
DOI:10.1039/C6TA06832D
Nanostructured α-MgAgSb has been demonstrated as a good p-type thermoelectric material candidate for low temperature power generation. Nevertheless, the intrinsic defect physics that impedes further enhancement of its thermoelectric performance is still unknown. Here we first unveil that an Ag vacancy is a dominant intrinsic point defect in α-MgAgSb and has a low defect formation energy, shown by first-principles calculations. In addition, the formation of an Ag vacancy could increase the crystal stability. More importantly, intrinsic point defects, namely an Ag vacancy, can be rationally engineered via simply controlling the hot press temperature, due to the recovery effect. Collectively, a high peak ZT of ∼1.3 and average ZT of ∼1.1 are achieved when hot pressed at 533 K. These results elucidate the pivotal role of intrinsic point defects in α-MgAgSb and further highlight that point defect engineering is an effective approach to optimize the thermoelectric properties.
Co-reporter:Jing Li, Li-Dong Zhao, Jiehe Sui, David Berardan, Wei Cai and Nita Dragoe
Dalton Transactions 2015 - vol. 44(Issue 5) pp:NaN2293-2293
Publication Date(Web):2014/12/11
DOI:10.1039/C4DT03556A
In the past few years, many studies have been devoted to the thermoelectric properties of copper selenides and sulfides, and several families of materials have been developed with promising performances. In this paper, we report on the synthesis and thermoelectric properties of Na-doped BaCu2Se2 from 20 K to 773 K. By Na doping at the Ba site, the electrical conductivity can be increased by 2 orders of magnitude, and the power factor can reach 8.2 μW cm−1 K−2 at 773 K. Combined with a low thermal conductivity of 0.65 W m−1 K−1, a ZT of 1.0 has been obtained for Ba0.925Na0.075Cu2Se2 at 773 K, which is the highest value reported in this family to date. However, BaCu2Se2 volatilizes at 473 K, so a protective coating is necessary for its application. Besides, we studied the thermal expansion coefficient of BaCu2Se2 in this paper.
Co-reporter:Jiehe Sui, Cheng Zhang, Da Hong, Jing Li, Qian Cheng, Zhiguo Li and Wei Cai
Journal of Materials Chemistry A 2012 - vol. 22(Issue 27) pp:NaN13681-13681
Publication Date(Web):2012/05/18
DOI:10.1039/C2JM31905E
Monodisperse ZnFe2O4 nanoparticles with sizes less than 10 nm have been successfully assembled on multi-walled carbon nanotubes (MWCNTs) by in situ high-temperature decomposition of the precursor iron(III) acetylacetonate, zinc acetate and MWCNTs in polyol solution. A possible formation mechanism was proposed, which suggests that the ZnFe2O4 nanoparticles are formed on the surface of MWCNTs through an aggregation thermochemical reaction process between ZnO and γ-Fe2O3 subparticles. It was found that the coverage density on the MWCNTs could be easily controlled by changing the concentration of the precursor. As anode materials for Li-ion batteries, the MWCNT–ZnFe2O4 nanocomposites showed high rate capability and superior cycling stability with a specific capacity of 1152 mA h g−1, which was much higher than that of ZnFe2O4 nanoparticles. The MWCNTs served as good electron conductors and volume buffers in improving the lithium performance of MWCNT–ZnFe2O4 nanocomposites during the discharge–charge process. Magnetic measurements showed that the MWCNT–ZnFe2O4 nanocomposites are superparamagnetic at room temperature and the magnetization of the samples can be controlled by the reaction conditions. The as-synthesized MWCNT–ZnFe2O4 nanocomposites are water dispersible and can be manipulated by an external magnetic field. Therefore, the nanocomposites have significant potential for application in the fields of energy storage, composites, wastewater treatment and biomaterials.
Co-reporter:Songting Cai, Zihang Liu, Jianyong Sun, Rui Li, Weidong Fei and Jiehe Sui
Dalton Transactions 2015 - vol. 44(Issue 3) pp:NaN1051-1051
Publication Date(Web):2014/11/05
DOI:10.1039/C4DT03059A
AgSbSe2 possesses extremely low thermal conductivity and high Seebeck coefficient, but the low electronic conductivity leads to a low ZT value. In this paper, Na is used to substitute Sb to improve the electronic conductivity. The results show that Na doping not only improves the power factor caused by the enhanced carrier concentration, but also decreases the thermal conductivity due to point defects, nanoscale stacking faults and Na-rich precipitate. Consequently, a high ZT value of 0.92 is achieved in the AgSb0.99Na0.01Se2 sample.
Co-reporter:Zihang Liu, Huiyuan Geng, Jing Shuai, Zhengyun Wang, Jun Mao, Dezhi Wang, Qing Jie, Wei Cai, Jiehe Sui and Zhifeng Ren
Journal of Materials Chemistry A 2015 - vol. 3(Issue 40) pp:NaN10450-10450
Publication Date(Web):2015/07/03
DOI:10.1039/C5TC01560J
The effect of Ni doping on both electron and phonon transport properties of nanostructured CoSbS has been investigated in this study. We found a more than 2 times increase on figure-of-merit (ZT). The noticeable enhancement is mainly attributed to the optimized carrier concentration, high effective mass and strong electron–phonon scattering upon Ni doping. A ZT of 0.5 was achieved at 873 K together with a power factor of 20 μW cm−1 K−2 for the Ni doped CoSbS samples. The reduced lattice thermal conductivity via the strong electron–phonon scattering for Ni doped CoSbS samples is confirmed by the quantitative calculation of the various phonon scattering mechanisms according to the Callaway model.
Co-reporter:Jing Shuai, Zihang Liu, Hee Seok Kim, Yumei Wang, Jun Mao, Ran He, Jiehe Sui and Zhifeng Ren
Journal of Materials Chemistry A 2016 - vol. 4(Issue 11) pp:NaN4320-4320
Publication Date(Web):2016/02/12
DOI:10.1039/C6TA00507A
Bi-based Zintl compounds, Ca1−xYbxMg2Bi2 with the structure of CaAl2Si2, have been successfully prepared by mechanical alloying followed by hot pressing. We found that the electrical conductivity, Seebeck coefficient, carrier concentration, and thermal conductivity can be adjusted by changing the Yb concentration. All Ca1−xYbxMg2Bi2 samples have low carrier concentrations (∼2.4 to 7.2 × 1018 cm−3) and high Hall mobility (∼119 to 153 cm2 V−1 s−1) near room temperature. The partial substitution of Ca with Yb causes structural disorders, which lowers the thermal conductivity. The highest figure of merit of ∼1.0 is observed in Ca0.5Yb0.5Mg2Bi2, and ∼0.8 in the unsubstituted CaMg2Bi2 and YbMg2Bi2. A small amount of free Bi was found in all the samples except YbMg2Bi2. By reducing the initial Bi concentration, we succeeded in obtaining phase pure samples in all compositions, which resulted in a much better thermoelectric performance, especially much higher (ZT)eng and a conversion efficiency near 11%. Such a high efficiency makes this material competitive with half-Heuslers and skutterudites.
