The Study Of WO₃ Function Ceramics Doped With High Valence Oxides

Tungsten trioxide (WO₃), as one kind of functional materials, has been investigated systematically because of its potential for technological applications, such as electrochromic devices, gas detection and chemical catalyst. In recent years, it has been found that doped WO₃ ceramics show good nonlinear electrical properties characterized by low breakdown voltage and low operating current.because the dielectric constant of WO₃ is high,it's possible for potential applications in micro-electronic area.However, compare with other varistor material,non-linear coefficient of WO₃ ceramics isn't high enough,the stability of I-V curve is debatable and serious hysteresis exist,so electrical behavior can not be explain with existing theory about nonlinear.So it has scientific and practical significant to investigate the detailed electronic properties of doped tungsten and involved physical principle. In this thesis, starting from fabricating WO₃ ceramics doped with high valence and alkali metal element oxides, the nonlinear electrical properties are mainly investigated to understand the physical mechanism of WO₃ functional materials.1) WO₃ ceramics doped with various quinquevalent element oxides are fabricated by the conventional solid-state reaction process. the microstructure, phase structure and nonlinear electrical properties properties of WO₃ ceramics were investigated and the results include:(1) Doping quinquevalent element in WO₃ ceramics can influence the grain size .dopant of V₂O₅,Nb₂O₅ and Ta₂O₅ can inhibit the grain growth.The grain size less than 5μm for all of the samples.As dopants, quinquevalent element mainly segregated at the grain boundaries.(2) There is only monoclinic phase of WO₃ existing in quinquevalent element-doped WO₃ ceramics, it is advantaged to improve stability of electrical properties under high electrical field and favorable to as piezoresistive material. (3) Doping of quinquevalent elements can not increase nonlinear coefficient of WO₃. The nonlinear coefficient is mainly in the range of 1～3.(4) I-V curve of WO₃ ceramics exist negative resistance phenomenan when percentage composition of Ta₂O₅ is 5%.2) The influence of doped with quinquevalent-alkali oxides on WO₃ ceramics is studied.It was found that WO₃ ceramics doped with quinquevalent-alkali oxides have compact structure and preferable nonlinear coefficient. in addition,electrical quality factor is steady,negative resistance isn't exist.3) The microstructure, phase structure and nonlinear electrical properties properties of WO₃ ceramics doped with two deffrent kinds of quinquevalent oxides (V₂O₅, Ta₂O₅) were investigated. Tungsten trioxide (WO₃) ceramics doped with vanadic pentoxide (V₂O₅) and tantalum pentoxide (Ta₂O₅) was prepared by conventional electronics ceramics method and effect of doping material on microstructure and electrical properties of tungsten trioxide (WO₃) ceramics. X-ray diffraction(XRD) revealed that anorthic crystal in tungsten trioxide (WO₃) ceramics was restrained to appear due to doping material, only single phase consist in WO₃ ceramics. The result of I-V test indicated that voltage-sensitive voltage(U_1mA) of (V₂O₅, Ta₂O₅)-doped tungsten trioxide (WO₃) ceramics obviously augment but non-linear coefficientαwas reduced.