Preparation And Characterization Of ZnO-based Compound Conductive Ceramics

As a functional material,ZnO-based compound conductive ceramic-s have the extensive application prospect s in the power electronics industry.For a long time,there have been some shortages in the prepara-tion and theory research that limit its industrial production.In this work,ZnO-ZnAl₂O₄-Mg O is served as the basic formula to study the inf-luence of the composition and sintering temperature on the micros truct-ure and electrical properties,and the new kind of high performance ZnO-based compound conductive ceramics that could be used in high frequency electric field have been prepared by the traditional solid phase sintering method successfully.Firstly,the influence of matrix composition on the microstructure a-nd electrical properties has been discussed in this work.The results sho-w as follows: When the concentration of Mg O is 5.00 mol%,asprepare-d samples with the change of Zn Al 2O4 content,sintered at 1320 oC,pos-sess continuously adjustable resistivity,in the range of 11.60 to 123.48 W·cm.in addition,the critical frequency of as-prepared samples exceed 0.67 M Hz,and the nonlinear coefficient is in the scope of 0.99 to 1.23.Considering Zr4 + would be introduced to the matrix in the process of industrial production,ZrO₂ is used as an important additive in the optim-al basic formula to study its effects on ZnO-based compound conductiv-e ceramics.It could be concluded that ZrO₂ exist in the matrix with less content could optimize electrical performance.The samples with the ZrO₂ concentration of 0.30 mol%,sintered at 1320 oC,possess the resistivity of 19.59 W·cm,the nonlinear coefficient of 1.01,the resist an-ce temperature coefficient of-2.60?10-3/o C,and the critical frequency of 1.20 M Hz.Then,NiO is selected as a composite phase in the optimal basic fo r-mula to overcome the shortages in compactness and sensitivity to sintering temperature.The results show as follows: The doping of NiO could decrease sintering temperature and improve the compactness significantly.The quaternary system could be obtaine d with the excelle-nt electricalproperties that the resistivity is 15.13 W·cm,the nonlinear coefficient is 1.05,the resistance temperature coefficient is-1.79?10-3/ oC,and the critical frequency is 1.25 M Hz,when the content of NiO is 7.00 mol% sintered at 1280 oC.In addition,the incorporation of Ni2 + in-to the ZnO lattice could reduce temperature gradient in the as-prepared samples and then weaken the sensitivity to the sintering temperature.In order to study the influence of sintering temperature on the electrical performance of as-prepared samples,the temperature range of 1280 oC to 1400 oC is chosen.The results show as follows: Sintering temperature has the significant effects on the electrical performance.With the temperature increasing,the progress of densification could be promoted,and the resistivity of grain and grain boundary would be decreased significantly.The weak interface effect would c ause the decrease of nonlinear coefficient and the increase of critical frequency,as the temperature rising.While sintering at much higher temperature would destroy the homogeneity of microstructure,which would cause the degradation of comprehensive electrical properties.It is worth attention that as-prepared samples could present the characters of linear I-V and stable impedance-frequency,which indicate the grain boundary barrier is weak and have no activity.What's more,the conductive mechanism main ly coincide with the models of thermal excitation and percolation conduction in ZnO-based compound conducti-ve ceramics.At the same time,Maxwell-Wagner interfacial polarizatio-n exist in the matrix that maintaines the stability of grain boundary effects.