H2S gas sensitive films based on ZnO QDs of 3.8 nm were prepared through a spin-coating process. The sensitivity of ZnO films was greatly improved after low-temperature processing and grain sizes remained below twice Debye length. A modified flat band diagram was proposed to explain this great improvement. The comparison of responses of ZnO films annealed at different temperatures was made and the sensors exhibited quick response and recovery. The response of ZnO films toward H2S of 68.5 ppm was a relatively high value of 75 at room temperature, which reached its highest value of 567 at 90 °C. The optimal operating temperature of 90 °C is relatively low compared to other gas sensors based on ZnO. Meanwhile, ZnO films showed good selectivity toward H2S against SO2, NO2 and NH3.

A multiferroic La0.7Ba0.3MnO3–BaTiO3 composite sample was prepared by the solid state method. The composite exhibits a ferroelectric feature (2Pr=10.52 µC/cm2, 2Ec=32.2 kV/cm) and weak ferromagnetic feature (2Mr=13.6 memu/g, 2Hc=60.5 Oe). More importantly magneto-electric coupling, as well as magneto-capacitance and magneto-impedance effects, was also observed. The average changes of the 2Pr and 2Ec were −21.1% and −9.2%, respectively, when a relatively low external magnetic field (H=200 Oe) was applied. The MC value was ~−1.9% at 1 MHz after the sample was magnetized. These ME effects were mainly originated from the coexistence of magnetostriction and magneto-resistance in LBMO.

The effects of Pb1.5Nb2O6.5 addition were investigated on the densification, phase evolution, microstructure, and microwave dielectric properties of 5ZnO·2B2O3 ceramics. It was shown that a 5.5 mol% addition of Pb1.5Nb2O6.5 to 5ZnO·2B2O3 ceramics successfully tailored its temperature coefficient of resonant frequency (τf) from −80 to ~0 ppm/°C and lowered its sintering temperature from 955 to 890 °C without degrading its microwave dielectric properties. 5ZnO·2B2O3 ceramics sintered at 890−910 °C for 3 h with 5.0−6.0 mol% Pb1.5Nb2O6.5 additions exhibited excellent microwave dielectric properties: εr=7.8−8.3, Q×f=11,500−15,200 GHz, and −9.2 ppm/°C≤τf≤+6.6 ppm/°C @ ~7.4 GHz. The ceramics showed cofiring compatibility with Ag and were therefore novel candidates for LTCC substrates.

An integrated passive impedance-loaded SAW H2S sensor working at room temperature has been presented in this paper. The sensor consists of a SAW transponder with delay line structure and a resistive H2S sensor as an impedance-loaded sensor. The SAW delay line was fabricated on a 128° LiNbO3 substrate and its center frequency is 233 MHz. The resistive sensor composed of the nano-crystalline SnO2 film and aluminum electrodes was also fabricated on the same substrate. The gas sensing properties of the resistive H2S sensor have been tested separately. In order to maximize the sensitivity of the whole sensor, the resistance of the impedance-loaded sensor was adjusted to match the output impedance of the SAW interdigital transducer (IDT) by changing the resistivity of the Sb-doped SnO2 nano-crystalline films and optimizing the electrode structure. The variation in the return loss magnitude was increased to 2.51 dB. Finally, the impedance-loaded SAW sensor was configured and measured wirelessly for various H2S concentrations at room temperature. The measurement results show that the proposed H2S sensor not only has good repeatability and high sensitivity but also is capable of passive wireless detection at room temperature.

Multiferroic magnetoelectric (ME) BaTiO3–CoFe2O4 (BTO–CFO) ceramic composites with different thicknesses were fabricated via tape casting technique. The interfacial morphology of the composite demonstrates the presence of plate-like grains with a thickness of ~400 nm. This could be associated with the residual stresses originated from lattice mismatch and different thermal expansion coefficients between BTO and CFO layers. The dielectric constant, piezoelectric constant, and ferroelectric properties of the multilayered composite are degraded in the presence of CFO layers in comparison with those of BTO bulk. Furthermore, the dielectric constant and polarization of the composite decrease with increasing frequency. The leakage current density and magnetic remanence ratio of the composite reach up to the order of 10−6 A/cm2 and 40 %, respectively. The direct and converse ME coefficients were measured to be 8.1 μV/cm Oe and 1.1 × 10−3 G/V, respectively. Based on the converse ME effect, an electrically controlled ME inductor was designed using the composite as its core. The inductance and tunability of the inductor increase with increase of applied dc electric field.

The effects of the Nb-dopant content and the sintering conditions on the electrical properties and the positive temperature coefficient of resistance (PTCR) effect of Ba1.005(Ti1−xNbx)O3 (BTN) ceramics were investigated, which were sintered at 1,070–1,220 °C for 0.5–6 h in a reducing atmosphere and then re-oxidized at 600–750 °C for 1 h. The results indicated that both the sintering temperature and sintering time affected the electrical properties and the PTCR effect of the multilayer BTN samples, whose room-temperature (RT) resistance first reduced and then increased as a function of the donor–doped concentration at all sintering temperature; moreover, the higher the sintering temperature was, the lower the critical dopant concentration. The BTN ceramics showed a remarkable PTCR effect, with a resistance jump greater by 3.3 orders of magnitude, along with a low RT resistance of 0.3 Ω at a low reoxidated temperature of 600 °C after sintering in a reducing atmosphere.

This paper presents the structural, ferroelectric, ferromagnetic, resonance and magnetoelectric (ME) properties of multilayered ME composites fabricated using tape casting method. The compositions corresponding to CoFe2O4 (CFO) with particle size of ~150 nm and BaTiO3 (BTO) with particle size of ~100 nm were chosen as ferromagnetic and ferroelectric phases, respectively. Delamination was found at the interface between CFO and BTO layers, which was related to the residual stress due to the difference in thermal expansion coefficient between the two layers. The largest direct magnetoelectric and converse magnetoelectric coefficients of the multilayered ME composite were, respectively, 36 μV/cm Oe at a bias magnetic field of 2,800 Oe and 1.16 × 10−3 G/V at a frequency of 30 kHz. In addition, the corresponding interfacial coupling coefficient was calculated to be 3.2 × 10−5. For the multilayered ME composite, a resonance frequency of 4.96 MHz and a bandwidth of 40 kHz were obtained using capacitance-frequency spectrum method.

The model of gradient distributed oxygen vacancies is extensionally investigated. Based on the dynamics of oxygen vacancies under diffusion and exclusion effects in cooling process, the steady state and non-steady state solutions of the diffusion equation of the vacancies are solved. The transient distribution of oxygen vacancies is revealed during the idealized cooling process. It is concluded that the exclusion effect dominates the density distribution of oxygen vacancies throughout the crystallite. The time-dependent expressions of potential barrier [qV(x,t)], film resistance (R) and response to reducing gases (S) are formulated on the basis of Schottky model and Poisson's equation. The simulated gas sensing characteristics are in good correlation with experimental results. The constants and variables are estimated according to the correlation. Presumptions and reservations of the present expressions are also discussed.

This paper proposed a two-stage thermal processing method combined with the reduction-reoxidation procedure. Samples were firstly sintered in a reducing atmosphere by two stages and then reoxidized in air. Such two-stage thermal processing method was used to adjust density and grain size of ceramics separately. Finally, nanocrystalline semiconducting donor-doped BaTiO3 ceramics were first successfully prepared. Samples with average grain size of 340 nm exhibited unexpectedly low room resistivity of 136 Ω cm and a significant PTCR effect, with a resistance jump of 4 orders of magnitude. In addition, depletion layer thickness of 40 nm and surface acceptor-state densities of 9.52 × 1013 cm−2 were also calculated. Such good properties had not been reported in former publications. It also means that smaller components based on semiconducting BaTiO3 ceramics could be produced and more extensive application field could be proposed in the trend of miniaturization of electronic devices.

•BGFO ceramics exhibited high density, strong ferroelectricity, and good magnetism.•BGFO ceramics exhibited typical relaxor behavior.•There are different conductivity mechanisms at different temperatures for BGFO.Multiferroic Bi0.8Gd0.2FeO3 (BGFO) ceramics were prepared by a rapid-liquid phase sintering process. BGFO ceramics can be sintered at a sintering temperature range of 875 °C–940 °C and shown a pure orthorhombic (space group, Pnma) structure. The crystal symmetry and lattice parameters were determined from the Rietveld analysis for the experimental data. BGFO ceramics sintered at 900 °C exhibited high theoretical relative density (∼98%), strong ferroelectricity and good magnetism. BGFO ceramics exhibited the similar dielectric relaxation properties to the typical relaxor ferroelectrics. The role of oxygen vacancies at high temperature in dielectric and ac conductivity behavior was also discussed. The diffusing of structure defects between the grain and grain boundary was established using Impedance Spectroscopy (IS).