Recent experiments revealed that the Mg–Zr codoped Ta3N5 semiconductor exhibited improved photoelectrochemical activities, but the role of Mg–Zr codoping in the improved photoelectrochemical activity remained unclear. In this study, the density functional theory calculations were preformed to investigate the electronic structures and thermodynamic properties of the Mg–Zr codoped Ta3N5. The results showed that Mg and Zr dopants had nearly the same effects on the electronic structures of Ta3N5, while the thermodynamic properties of Mg and Zr in Ta3N5 were different. The Zr dopant preferentially substituted the Ta atom and compensated for oxygen impurities and nitrogen vacancies, resulting in the cathodic shift of the onset potential of Ta3N5. The Mg dopant preferentially occupied the interstitial site and acted as a delocalized electron donor, contributing to the enhanced photocurrent.

After sixteen successive passes of equal channel angular pressing (ECAP), kinked 18R-LPSO phase and refined DRX grains were developed in Mg94Y4Zn2 alloy. Simultaneously, nano-sized 14H micro cells and Mg24Y5 particles were dynamically precipitated. Owing to the above microstructure characteristics, the 16p-ECAP alloy exhibited outstanding mechanical property with compressive strength and fracture strain of 611 MPa and 20.1%, respectively.

A recent experiment revealed that the Ta3N5 semiconductor with orientation along the (110) surface exhibited improved photoelectrochemical activities, but the role of the (110) surface in the improved photoelectrochemical activity remains unclear. In this study, density functional theory calculations were performed to investigate the surface stabilities, surface electronic structures and water splitting behavior of the Ta3N5(110) surface with and without oxygen impurities. The results showed that, on the clean and oxygen impurity containing (110) surfaces, the energy barriers of water splitting were as low as 0.05 and 0.06 eV, respectively, suggesting that the Ta3N5(110) surface is a promising candidate for water splitting. The lower energy barriers of water splitting on the Ta3N5(110) surface may be ascribed to the easy migration of the H atom from the surface Ta atom to the nearby N atom. Furthermore, the surface energies and surface electronic structures revealed that the Ta3N5(110) surface contained less oxygen impurities, which is in accordance with the experimental observations.

Equal channel angular pressing(ECAP) as a common severe plastic deformation (SPD) procedure has been extensively explored in Mg alloys to improve their mechanical properties. But due to the hot processing temperature and texture softening, the strength of ECAP processed Mg alloys was found to be relatively low. In this work, high strength and good ductility were achieved in ZK60 magnesium alloy by a combination of grain refinement strengthening and precipitate hardening through the use of heat treatment and equal channel angular pressing (ECAP). Due to the pre-solution heat treatment, fine metastable phase particles (MgZn2) precipitated during the severe plastic deformation, which improved the work hardening of the alloy and increased the strength and ductility simultaneously. When the ECAP processing temperature was reduced gradually, the grains were further refined to ~500 nm and more MgZn2 particles precipitated hierarchically. Therefore, there was a notable increase in the yield strength and ultimate tensile strength, while the ductility was almost retained.

•Profuse micro-sized needle-like phases precipitated in T6-treated Mg–Al–Gd alloy.•Parallel 18R LPSO phases and crossed Mg5Gd-type ones occupied different grains.•Continuous and compact oxidation film was formed on the surface of T6-treated alloy.•The corrosion resistance has been significantly improved after T6 heat treatment.•The main corrosion mechanism of T4-treated alloy is intergranular corrosion.Microstructural evolution of a new Mg–Al–Gd alloy during heat treatment and its corrosion behavior in 1 wt.% NaCl solution were investigated by morphological observation, hydrogen evolution and electrochemical measurements. The microstructure of the as-cast alloy mainly consists of α-Mg, network-like Mg5Gd and polygonal Al2Gd phases, while a considerable part of Mg5Gd ones dissolve after T4 treatment. After T6 treatment, profuse micro-sized needle-like precipitates including crossed Mg5Gd-type and parallel Mg12ZnY-type ones appear and occupy different grains. These precipitates, resulting in homogeneous corrosion, continuous and compact oxidation film on the surface, have significantly improved the corrosion resistance of the Mg alloy.

The Ta3N5 semiconductor photocatalyst possesses a 720 nm (about 1.72 eV) sub-band-gap optical absorption but the mechanism of this optical absorption is still controversial. In this study, the hybrid density functional theory calculations are performed to unravel the mechanism of 720 nm sub-band-gap optical absorption of Ta3N5. By studying the possible optical absorption initiated by the ON impurity and the VN defect, we find that the 720 nm sub-band-gap optical absorption of Ta3N5 may be ascribed to the electron transition from to . In addition, we propose that the 720 nm sub-band-gap optical absorption can be used to qualitatively evaluate the photocatalytic water splitting ability of Ta3N5.

•Microstructure refinement and homogeneity of the Mg alloy with LPSO phase were attained after SS plus ECAP.•The refined microstructure resulted in higher strength and better ductility.•The fine-grained alloy was easily rolled into a thin sheet without edge cracking and with high productivity.•The combination processing has a great potential in producing Mg alloys with excellent overall performance.A fine-grained Mg–1.8Gd–1Zn–0.1Zr (at.%) alloy with long-period stacking ordered (LPSO) phase was obtained via solid-solution(SS) treatment plus multi-pass equal-channel angular pressing(ECAP). The effects of post-ECAP rolling on microstructure change and deformation characteristic of the Mg alloy were investigated. The results showed that the fine-grained alloy after 16 ECAP passes at 658 K had a yield strength of 334.4 MPa with an elongation of 22.5%. Grain refinement with LPSO formation simultaneously improved the strength and ductility of the ECAPed alloy, indicating a good plastic formability. The ECAPed Mg sheet was easily rolled at 773 K from 1.5 mm to 0.24 mm in thickness without edge cracking. After rolling, the fine-grained Mg alloy exhibited higher tensile strength with appropriate elongation. The post-ECAP rolling has been successfully used in the high productivity of Mg thin sheet with good mechanical properties.

Two kinds of Mg-Zn-Mn-Ca alloys with and without cerium were designed and fabricated. In-vitro degradation tests and electrochemical evaluations were carried out to compare their biocorrosion behavior in Hank's solution at 37 °C. After adding cerium, the continuous network distributed Ca2Mg6Zn3 phases in Mg-2Zn-0.5Mn-1Ca alloy (Alloy I) were separated due to the emerging non-continuously distributed Mg2Ca phase and Mg12CeZn phase. This change led to corrosion acceleration of Mg matrix at the initial stage but also sped up the formation of compact corrosion products for Mg-2Zn-0.5Mn-1Ca-1.5Ce alloy (Alloy II), and therefore enhanced its biocorrosion resistance. Cerium containing Alloy II has the potential to be used as future biomaterials.Nyquist plots of the samples after immersion in Hank's solution for 1 h (a), 2 d (b), 10 d (c) and equivalent circuit of the samples (d)

The molecular dynamics simulations are performed to explore the fracture behavior and the ductility of the twinned Cu nanowires containing orthogonally oriented growth CTBs due to the uniaxial tensile deformation. The results reveal that, the fracture behavior and the ductility of the twinned nanowires are not related to the length of the nanowires but also intensively related to the twin boundary spacing. When the twin boundary space is changed, the twinned nanowires undergo three distinct failure modes which include ductile fracture, brittle fracture and ductile-to-brittle transition depending on the length of the nanowires. We also find a reduction in the ductility of the twinned nanowires, which is ascribed to the deformation localization induced by the Lomer dislocation and the rapid necking resulted from the twinning partial slipping. Finally, the atomic-level process that occurs during deformation until final fracture are examined in detail, and a new formation mechanism of the Lomer dislocation is observed when a 90° partial dislocation transmits across a coherent twin boundary.

Continuous surface nanocrystallization (SNC) of rebar was achieved through wire-brushing process. A uniform NC layer with thickness of 25 μm and average grain size of 50 nm was formed on the rebar surface. Due to the enhanced passivation performance of the NC layer, corrosion resistance of the SNC rebar was significantly improved in Cl−-containing saturated Ca(OH)2 solution. High-energetic crystal defects of the nano-grains leads to the faster passivation and enhanced stability of the passive film of the SNC rebar.

•The ultrafine-grained Cu–Mg alloys were fabricated after ECAP plus cold working.•The UFG alloys have the higher strength and fairly good electrical conductivity.•The combination processing produced Cu alloys with excellent overall performance.•The UFG alloys have a great potential in highspeed electrification railway systems.A Cu–0.2 wt%Mg alloy and a Cu–0.4 wt%Mg alloy after Conform-process were deformed by equal channel angular pressing (ECAP) and subsequent cold working (CW) at room temperature, aim to obtain excellent overall performance for new commercial contact wires. The ECAP plus CW procedure made the grains of the two alloys obviously ultra-fine and elongated, which significantly increased their micro-hardness and tensile strength while maintained a fairly good electrical conductivity. After annealing at 573 K, the tensile strength of the two ECAP + CW-processed alloys reduced, but the electrical conductivity and ductility increased. The combination processing can endow the two Cu–Mg alloys high strength and good conductivity, which are advantageous to the current high-frequency electrification railway systems.

•High strength and good ductility were simultaneously achieved in the Mg–9Al–1Zn alloy by the solution + ECAP + aging procedure.•Pre-solution treatment accelerated the grain refinement and strengthening.•Hierarchical precipitates formed during ECAP and the subsequent aging.•Equilibrium structure facilitated the aging hardening.Magnesium alloy processed by equal channel angular processing (ECAP) usually had a good ductility, but often inadequate strength. Herein, an approach was developed to simultaneously achieve high strength and good ductility in the Mg–9Al–1Zn alloy. This approach involved pre-solution treatment, ECAP and subsequent aging. The pre-solution accelerated the grain refinement and increased the strain hardening during the ECAP that improved the strength of the alloy. The spherical big precipitates and dispersed nanosized fine precipitates generated separately during the ECAP and the following aging process. As increasing the ECAP passes from 4 to 12, the strain hardening decreased but the fine structure became more equilibrium. Moreover, the aging hardening became more effective that resulted in a good ductility and a high strength in the Mg–9Al–1Zn alloy.

•The β-Mg5(Gd,Zn) phases partially and gradually dissolved during increasing ECAP process.•Profuse LPSO microcells with a width of 0.25–0.5 μm and a length of 0.5–1.5 μm were produced.•A large number of DRX grains were formed adjacent to the LPSO microcells and grain boundary β-Mg5(Gd,Zn) phases.•High mechanical properties were obtained in the 16-pass Mg–Gd–Zn–Zr alloy.A cast Mg97.1Gd1.8Zn1Zr0.1 (at.%) alloy having long period stacking ordered (LPSO) structures was continuously processed at 375 °C by equal channel angular pressing (ECAP) for 1, 4, 8, 12 and 16 passes. With increasing ECAP passes, more and more rectangular microcells with a width of 0.25–0.5 μm and a length of 0.5–1.5 μm were produced adjacent to the β-phase particles and dynamic recrystallization (DRX) grains. These microcells were actually sandwichs consisting of 14H LPSO phase and α-Mg nano-slices, resulting from the shear effect and high internal temperature of the billet generated by continuous ECAP process. After 16 passes, the ultimate tensile strength of 387 MPa and the elongation of 23% were obtained due to the special microstructure in the alloy.

•UFG steel with a ferrite grain size of 200 nm is processed with 16 passes of ECAP.•The Fe3C particles are dispersed in ferrite matrix of the UFG steel.•It corrupts relatively rapidly, but shows better anodic passivity properties in acid.A bulk ultrafine-grained (UFG) mild steel with a ferrite grain size of approximately 200 nm and a dispersed distribution of iron carbide particles was fabricated by equal-channel angular pressing (ECAP) at 400 °C. The corrosion behaviour of the ECAP-processed mild steel and pure iron was investigated in a 0.5 mol/L H2SO4 solution. They exhibited a higher corrosion rate and better anodic passivity properties due to the presence of more crystalline defects. As a result of the refinement of the iron carbide particles, the forming ability of a continuous dense passive film was improved.

We report an effective approach to achieve an excellent combination of high strength and good ductility in the AZ91 Mg alloy. The approach involves solution heat treatment, equal channel angular pressing (ECAP) and subsequent aging. This approach is effective in accumulating dislocations and promoting the formation of large spherical precipitates during ECAP. The aging produced much finer precipitates with uniform distribution inside the grains. The hierarchical precipitate structure produced by the current approach rendered high strength and good ductility.

The biodegradation behavior of an ultrafine-grained (UFG) magnesium alloy ZE41A containing rare-earth (RE), obtained through multi-pass of equal channel angular pressing(EACP), was investigated by electrochemical measurements in Hank's solution. The highest value of charge transfer resistance was obtained in the electrochemical impedance spectroscopy plots of the ECAPed samples with the largest pressing pass, while a movement of corrosion potential toward noble direction and a decrement of corrosion current density were observed in the potentiodynamic polarization curves of the ECAPed samples with further pressing passes. These results indicated that ECAP could be an efficient way to reduce the biodegradation rate of the ZE41A alloy.

By micro-arc oxidation (MAO) process in a silicate electrolyte, the oxide coatings were successfully formed on a coarse-grained casting AZ91D Mg alloy and an ultra-fine grained (UFG) one fabricated by equal-channel-angular-pressing (ECAP). The effect of substrate microstructure on morphologies and corrosion resistance of the MAO coatings on AZ91D alloys were investigated by scanning electron microscopy observation, immersion tests and electrochemical impedance spectrum (EIS) measurements. In comparison, the MAO coating on the UFG Mg alloy has lower corrosion rate and larger Rf value. Three factors enhance the corrosion resistance. The first is the MAO coating with uniform size and distribution of micro-pores due to homogenous micro-arc discharge. Secondly, the number of open holes decreases due to the finer β-phase after ECAP process. The most important one is the higher compactness and thickness of the coating on the UFG Mg alloy. It implies that the MAO coatings have a great potential in surface protection of UFG Mg alloys.Highlights► The compacter and thicker MAO coating was formed on the UFG Mg alloy. ► The MAO coating on the UFG Mg alloy had the lower corrosion rate and larger Rf value. ► The MAO coatings have a great potential in surface protection of UFG Mg alloys. ► Improving mechanical properties and corrosion resistance of Mg alloys via ECAP + MAO.

•A deformed surface layer with fine grains was formed in a low-carbon steel by SFPB.•The top surface layer contained many dislocations and micro-cracks.•The fine-grained surface layer had a higher corrosion rate in a 3.5% NaCl solution.•The SFPB improved the passivity and pitting corrosion resistance of the steel.A grain refined surface layer thicker than 15 μm was fabricated on a low-carbon steel by supersonic fine-particles bombarding (SFPB). The microstructure and electrochemical corrosion properties of the original and the SFPB treated (SFPB-ed) low-carbon steel were characterized by optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and corrosion tests. The results showed that the microstructure of the top surface layer was refined to fine grains with the grain size about 3 μm by SFPB. Dislocation tangles and dense dislocation cells about 500 nm in width were formed in the refined grains. Large amounts of micro-cracks were introduced into the surface layer of the SFPB-ed sample, which led to the increase of its surface roughness. The SFPB treatment accelerated the corrosion of the low-carbon steel in a neutral 3.5 wt.% NaCl solution. The surface layer of the SFPB-ed low-carbon steel was dissolved after a certain time of corrosion, which led to the decrease of its corrosion rate. In a saturated Ca(OH)2 solution with and without Cl−, the micro-cracks in the surface layer of the SFPB-ed sample did not degrade its passivity properties and pitting resistance, which was due to the superior re-passivation properties of the abundant crystalline defects in its surface layer, such as grain boundaries and dislocations.

In this paper, an InGaN metal-insulator-semiconductor (MIS) photodetector with an ultra-thin Al2O3 insulation layer deposited by atomic layer deposition (ALD) was studied. A high photoelectric responsivity of 0.25 A/W and a spectral responsivity rejection ratio of about three orders of magnitude at 1 V reverse bias were achieved for this MIS photodetector. The dominant carrier transport mechanism in the InGaN MIS photodetectors is submitted to the space charge limited current (SCLC) mechanism at high field and exhibits an Ohmic-like conduction at low electric field. The results indicate that the ultra-thin Al2O3 film deposited by the ALD technique can act as an excellent insulation dielectric for the InGaN photodetectors.

Ultrafine-grained (UFG) Al-26 wt% Si alloy was obtained through multipass equal-channel angular pressing (EACP) procedure and subsequently tested in 3.5 wt% NaCl solution for the evaluation of electrochemical corrosion. The results show that the ECAPed alloy with increased number of pressing passes obtain lower mass-loss ratios, nobler Ecorr and Epit, lower Icorr values, and higher anode polarization. The improved corrosion resistance of the ECAPed alloy results from the homogeneous UFG structure with the breakage of brittle large primary silicon crystals, which contributes to a higher pitting resistance. The oxidation product with improved adhesion force and protection efficacy can be formed with greater ease on UFG alloys. It implies that grain refinement through severe-plastic-deformation can enhance anticorrosion behavior of hypereutectic Al–Si alloys, besides the well-known strengthening and toughening effects.

In order to develop the eco-friendly Zn-rich coatings with higher corrosion resistance and lower pigment contents, several series of coatings were designed and manufactured employing lamellar Zn (Al) pigments mixed with silicone-acrylate emulsion modified inorganic silicate vehicle, and then were evaluated by conventional methods and the electrochemical method. The results indicated that the pigment contents reduced to approximate 25 mass% with lamellar Zn or (Zn and Al) pigments as substitute for spherical Zn pigments, and pigment mixtures were homogeneously dispersed due to silicone-acrylate emulsion moistening modification. Furthermore, the optimal coating had good coating properties (adhesion grade: one), acid resistance (lower mass losses) and anti-corrosive performance (improved corrosion potential and anodic passivation). The experimental results indicated that the modified lamellar Zn (Al) coating was suitable for large-scale spread and application on protecting steel structures in the hostile environment.

Shape-stabilized phase change materials (PCMs) exhibit desirable thermal storage properties and are used for energy conservation systems. This study is focused on the preparation and thermal-/dynamic-mechanical properties of the bulk porous Al foams impregnated with organic PCMs such as paraffins and stearic acid. The results indicated that the new shape-stabilized PCMs composites could be produced by a simple and eco-friendly constant-pressure impregnation method. The filling fraction of PCMs was approximately more than 80% for the impregnated samples with vacuuming or without vacuuming. The shape-stabilized PCMs/Al-foam composites exhibited considerable latent thermal storage potential for good interface, desirable phase-change temperature range and latent heat values (72.9 kJ/kg for the paraffin/Al-foam composite and 66.7 kJ/kg for the stearic acid/Al-foam composite). Moreover, the impregnation of PCMs improved the dynamic-compression yield strength, durability and resistance to oxidation of Al foams and made its ideal energy-saving materials.

In this work, the mechanical properties of equal channel angular processing (ECAP)-processed fine- and coarse-grained Cu–11.42Al–0.35Be–0.18B shape memory alloys (wt.%) were evaluated using tensile testing. After eight passes of ECAP and subsequently quenching from 600 °C to RT, the mean grain diameter was refined from 227 μm to 42 μm with grain boundaries purified. The fine-grained alloy exhibited good mechanical properties with a high tensile strength (703 MPa) and featured deeper and closer dimples on its fracture surface. The micro cracks were more refined, and the cracks extension along the grain boundaries was improved in the fine-grained alloy. These changes can be attributed to improvement of martensite morphology, structural refinement and grain boundary purification.

Significant corrosion resistance improvement was achieved in solid-solution treated (T4) Al-Cu alloy after severe grain refinement through equal-channel angular pressing. The bulk ultrafine-grained Al-Cu alloy with grain sizes of 200-300 nm has higher pitting potential (elevated by about 34 mV, SCE) and lower corrosion current density (decreased by about 3.88 µA/cm2) in polarization tests than the as-T4 alloy, and increased polarization resistance (increased by about 5.7 kΩ·cm2) in electrochemical impendence spectrum tests, along with alleviated corrosion damage in immersion tests. Two factors responds to the improved corrosion resistance of the alloy: the first is the refinement of residual θ-phase (Al2Cu) particles leading to the lower micro-galvanic currents and reduced susceptibilities to pitting corrosion, the second is the mass of strain-induced crystalline defects providing more nucleation sites for the formation of more volume fractions of stable oxide film.

Equal channel angular pressing (ECAP) was applied to modify the microstructures of Cu–Al–Be–B shape memory alloys (SMAs). The alloy was greatly refined because of the interaction of the large plastic deformation and physicochemical effects. With an increase of ECAP passes, the specimens showed a change from plastic fracture to brittle fracture, increased proportion of transgranular fracture, and decreased ultimate strength from 460 MPa to 340 MPa. These were caused by the precipitation of the γ2-phase and the disappearance of thermoelastic martensite. After appropriate heat treatment, the content of thermoelastic martensites increased, while the grain size remained smaller than that of the as-cast alloy. Further tests showed that the ultimate strength of this alloy improved to 703 MPa and the attenuation of shape recovery ratio was alleviated.

Ultra-fine-grained (UFG) ZE41A aeronautic magnesium alloy was achieved through multi-pass equal-channel angular pressing (EACP) at 603 K and subsequently tested in tension from room temperature (RT) to 588 K. An extraordinary phenomenon was first observed, improving both ductility and strength of hcp-structured UFG Mg alloy after a large number of ECAP passes. The results demonstrate the pressed ZE41A alloy after 8 passes has higher tensile strength but relatively lower ductility than the unpressed sample from RT to 423 K, whereas the tensile yield strength, ultimate strength, elongation to failure of UFG alloy after enough passes are all remarkably increased (about 120% higher in yield strength and 75% larger in elongation at RT after 32 passes). Multi-pass ECAP provides a simple and effective procedure for grain refinement of hcp-structured Mg alloy at elevated temperature undergoing dynamic recrystallization, while simultaneously improve its strength and ductility at service temperature owing to higher fraction of high-angle grain boundaries and lower intragranular dislocation density, making UFG Mg alloys more attractive in high strength structural applications.

Phase compositions and microstructure evolutions of three Mg–Y–Zn cast alloys during isothermal annealing at 773 K have been systematically investigated to clarify the formation behavior of 14H long period stacking ordered (LPSO) structure from α-Mg grains. The annealed microstructure characteristics indicate that the 18R phase is thermal stable in Mg86Y8Zn6 alloy where 18R serves as matrix, and 14H lamellar phase only forms within tiny α-Mg slices (less than 1% for volume fraction). The α-Mg grains in Mg88Y8Zn4 and Mg89Y8Zn3 alloys exhibit cellular shape, and 14H phase forms and develops into lamellar shape in these cellular grains after annealing. The results suggest that the presence of α-Mg grains is a requirement for the generation of 14H phase. The nucleation and growth rates of 14H lamellas are accelerated in α-Mg grains with higher concentrations of stacking faults and solute atoms. Moreover, the 14H lamellas are parallel to adjacent 18R plates in Mg86Y8Zn6 alloy, but the 14H phase precipitated in cellular α-Mg grains of Mg88Y8Zn4 and Mg89Y8Zn3 alloys exhibits random orientation relationship with surrounding 18R phase, indicating that the orientation relationship between 14H and 18R phases depends on the relationship between α-Mg grains and 18R phase.

•A two-step dynamic recrystallization for Mg97Y2Zn1 alloy during SPD is proposed.•18R LPSO promotes the first-step DRX in early passes of ECAP.•14H LPSO promotes the second-step DRX in later period of ECAP.•Refined microstructure contributes more to enhancement of ductility than strength.To explore the refinement mechanism of long period stacking ordered (LPSO) phases and its impact on mechanical properties, a typical Mg97Y2Zn1 alloy with α-Mg/LPSO binary microstructure prepared by multi-pass ECAP was systematically investigated. The obtained results indicate that during severe deformation the network 18R phase undergoes a three-step refining process, which includes kinking, zigzagging, and breaking. Lamellar 14H is precipitated first during early ECAP, and then is refined during further ECAP following a similar refining sequence of 18R phase. Moreover, a two-step dynamic recrystallization (DRX) is activated during deformation. In early passes of ECAP, DRX is promoted by 18R kinking through particle-stimulated nucleation (PSN) mechanism, and the precipitation of 14H lamellas suppresses DRX process in this period. After 14H lamellas became kinked, zigzagged and broken with more ECAP passes, the refined 14H accelerates the second step DRX process through PSN mechanism. In addition, owing to the significantly refined microstructures, both the strength and ductility of ECAP alloys increase. The ductility of ECAP alloy is improved remarkably with increasing ECAP passes. However, the increasing range of strength declines with further passes of ECAP, as the size of 18R stripes decreases gradually in the bimodal microstructures.

A recent experiment revealed that the Ta3N5 semiconductor with orientation along the (110) surface exhibited improved photoelectrochemical activities, but the role of the (110) surface in the improved photoelectrochemical activity remains unclear. In this study, density functional theory calculations were performed to investigate the surface stabilities, surface electronic structures and water splitting behavior of the Ta3N5(110) surface with and without oxygen impurities. The results showed that, on the clean and oxygen impurity containing (110) surfaces, the energy barriers of water splitting were as low as 0.05 and 0.06 eV, respectively, suggesting that the Ta3N5(110) surface is a promising candidate for water splitting. The lower energy barriers of water splitting on the Ta3N5(110) surface may be ascribed to the easy migration of the H atom from the surface Ta atom to the nearby N atom. Furthermore, the surface energies and surface electronic structures revealed that the Ta3N5(110) surface contained less oxygen impurities, which is in accordance with the experimental observations.

Recent experiments revealed that the Mg–Zr codoped Ta3N5 semiconductor exhibited improved photoelectrochemical activities, but the role of Mg–Zr codoping in the improved photoelectrochemical activity remained unclear. In this study, the density functional theory calculations were preformed to investigate the electronic structures and thermodynamic properties of the Mg–Zr codoped Ta3N5. The results showed that Mg and Zr dopants had nearly the same effects on the electronic structures of Ta3N5, while the thermodynamic properties of Mg and Zr in Ta3N5 were different. The Zr dopant preferentially substituted the Ta atom and compensated for oxygen impurities and nitrogen vacancies, resulting in the cathodic shift of the onset potential of Ta3N5. The Mg dopant preferentially occupied the interstitial site and acted as a delocalized electron donor, contributing to the enhanced photocurrent.

The Ta3N5 semiconductor photocatalyst possesses a 720 nm (about 1.72 eV) sub-band-gap optical absorption but the mechanism of this optical absorption is still controversial. In this study, the hybrid density functional theory calculations are performed to unravel the mechanism of 720 nm sub-band-gap optical absorption of Ta3N5. By studying the possible optical absorption initiated by the ON impurity and the VN defect, we find that the 720 nm sub-band-gap optical absorption of Ta3N5 may be ascribed to the electron transition from to . In addition, we propose that the 720 nm sub-band-gap optical absorption can be used to qualitatively evaluate the photocatalytic water splitting ability of Ta3N5.