| WO3 as an important functional material has widely device applications due to its electrochromic,photochromic and electrochemistry properties.In recent years,the non-ohmic behavior of WO3-based ceramics has been reported,indicating that WO3 is a potential varistor material.However,the electrical properties of WO3 ceramics are not stable,which is not favorable for the practical application in high voltage protection field.Usually,micron tungsten trioxide powders are used as the precursor to prepare the electronic ceramics with different composition by the traditional ceramic technologies.However,it has not been reported about electrical properties of WO3 ceramics used nanometer powders as precursor and prepared by different preparation technologies.In this work,we use nanometer powders as precursor to prepare the WO3 ceramics by the different kinds of technologies,and pay the most attentions to the electric properties in order to understand the physical mechanism of WO3 functional materials.1) Prepared the nanometer tungsten trioxide powder by using the sol-gel technology.The grain size is about 30nm,which was determined by the TEM and the wide X-ray diffraction method.2) The samples sintered in the Ar atmosphere are linear resistance with the resistivity of 0.77Ω·m.Otherwise,the samples sintered in air atmosphere present non-ohmic behaviour with the nonlinear coefficient of 3.67.3) It is found that the samples sintered at 900℃by the quenching technology had the nonlinear current-voltage properties and nonlinear coefficient could reach 10.93.However,the samples would become linear resistance when the quenching temperature above 900℃.The resistivity and potential barrier is only 0.16Ω·m and 0.049eV,respectively.In our opinion,the physical mechanisms of the non-linear characteristic are attributed to coexist of different phase structures in the samples,which make the barrier height and resistance between the grain boundaries increase.4) The microwave sintering make the WO3 ceramics transform into W18O49, which has stick shape grains and stable linear current-voltage characteristics.The globular shape grains are recovered when the samples were drawing tempered and the non-linear properties present again.The potential barrierφB is 0.15eV.5) The nonlinear coefficient of the samples first increase and then decrease with the increasing Gd2O3 nanopowder content.In our views,small amount of Gd element may limit the growth of the anorthic phase,reduce the nonlinear coefficient and the height of the barriers between the grain boundaries.In addition,the nano-size Gd2O3 will react with WO3 to produce the Gd2(WO4)3 phase with increasing Gd2O3.The potential barriers,nonlinear coefficient and grain boundary resistance will simultaneously increase.
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