Influence of Annealing Atmosphere on Varistor Property of TiO₂-Nb₂O₅-SrCO₃Ceramics

Varistor ceramics are typical electronic ceramics, which are widely used in circuits of overvoltage protection, high voltage stabilization and high energy surge absorption. TiO2 varistor ceramics has the advantages of low varistor voltage and good dielectric properties, but their low nonlinearity limited the application. The influence of annealing on the varistor properties of TiO2-Nb2O5-SrCO3 ceramics was investigated in this paper. TiO2-Nb2O5-SrCO3 varistor ceramics were prepared by the traditional method of ball grinding-forming-sintering and they were annealed in oxygen and nitrogen, respectively. The nonlinear coefficient α and the breakdown voltage EB of the samples were tested using the varistor dc parameter meter. The microstructure of samples was analyzed by XRD, SEM, STEM-EDAX and SAEDP. The results show that during annealing, Sr2+ ions with a larger radius obtain the kinetic energy and are segregated to grain boundaries, which increases the acceptor density of the grain boundaries and improves α. Annealing in an oxygen atmosphere, the enrichment of oxygen at grain boundaries is also helpful to increase the density of acceptor states and the height of the potential barrier, so as to further increase α. Meanwhile, annealing makes crystalline grains grow properly, which results in even grain size, reduces the porosity and increases the density of grains. So EB tends to reduce. As the doping concentration of Nb2O5 and SrCO3 is 0.15 mol%, respectively, and sintering temperature is 1300°C, TiO2-Nb2O5-SrCO3 varistor ceramics annealed in oxygen for 3 h at 750°C achieved the highest nonlinear coefficient α = 8.9 and the lowest breakdown voltage EB = 19.1 V·mm-1, which annealed in nitrogen achieved α = 8.4, EB = 20.6 V·mm-1, both superior to unannealed samples.

Annealing atmosphere-dependent capacitive energy storage

Electrostatic capacitors based on dielectrics with high energy density and efficiency are desired for modern electrical systems owing to their intrinsic fast charging-discharging speed and excellent reliability.The longstanding bottleneck is their relatively small energy density.Herein,we report enhanced energy density and efficiency in the Aurivillius Pb_(2)Bi_(4)Ti_(5)O_(18)films by controlling the post-annealing atmosphere.The results demonstrate that the fabrication atmosphere has significant effects on the film texture and defects.As the increase of the oxygen pressure of annealing atmosphere,the Pb_(2)Bi_(4)Ti_(5)O_(18)films show a preferred growth orientation of(00l)and fewer defects,which leads to a higher polarization and breakdown field for the film annealed in air atmosphere and thus help to achieve an ultrahigh energy density of59.4 J·cm^(-3)and an improved efficiency of 81.2%.Moreover,the film also exhibits excellent cycling reliability and good thermal stability.The Pb_(2)Bi_(4)Ti_(5)O_(18)films show a significant potential application for dielectric capacitors.

Effect of annealing atmospheres on the scintillation properties of Ce^(3+)‑doped YAG nanoscintillator

Background In this study,three sample detectors have been prepared by using cerium-activated YAG nanoscintillator(Y_(3)Al_(5)O_(12):Ce^(3+))synthesized by sol-gel method and heat-treat at 900°C for 2 h in different atmospheres such as vacuum,air and nitrogen.Purpose Many studies about YAG:Ce^(3+)single crystal have been carried out,but the material at the nanoscale remains not enough understood.The objective of the present paper is to investigate the effects of annealing atmosphere on the scintillation properties and identify the suitable atmosphere that allow to design radiation detectors with high scintillation efficiency.Methods In order to accurately assess the scintillation properties,the nanoscintillator sample powders have been designed as a detector,in which,preparation operations such as surface homogenization and efficiency coupling with photomultiplier tube(PMT)window were developed.The study was performed usingγ-rays 662 keV released from137Cs radioactive source,the bi-alkali GDB-4FF PMT was used as a photodetector.Nuclear instrumentation chain was set up in order to collect the pulse height spectra,NaI:Tl single-crystal scintillator was used as a reference detector to estimate the scintillation light yield.The delayed coincidence method was used for measuring the scintillation decay time of nanoscintillator sample detectors.Results The sample detector annealed at vacuum atmosphere exhibits the best scintillation properties,the scintillation light yield was estimated to be 14,600±3400 ph/MeV and the fast component in the scintillation decay was 90 ns.Conclusion The vacuum is the suitable atmosphere which allows the development of radiation detectors with high scintillation efficiency.

Ethanol sensing properties of Bi_(3.15)Nd_(0.85)Ti_3O_(12) films at low operating temperatures

Bi3.15Nd0.85Ti3O12 (BNdT) films were deposited on Pt/Ti/SiO2/Si(100) substrates by a metal organic decomposition (MOD)method, and annealed by a rapid thermal annealing process in oxygen atmosphere and in air, respectively. The crystalline structuresand morphologies of BNdT films were characterized by X-ray diffraction and field-emission scanning electron microscopy, and thegas sensing properties were measured by monitoring its resistance at different gas concentrations. The results indicate that the BNdTfilms annealed in air are of porous microstructure and rough surface, and the annealing atmosphere has great influence on gas sensingproperties. At an operating temperature of 100 °C, the BNdT films annealed in air are of high response value to 1×10?6 gaseousethanol, and the detecting limit is as low as 0.1×10?6. The corresponding response and recovery time is about 10 and 6 s, respectively.The results can offer useful guidelines for fabricating high performance ethanol sensors.