ZnO压敏陶瓷组成、微观结构与伏安特性研究

本文用电子自旋共振谱仪(ESR)、X—射线衍射仪(XRD)、扫描电镜(SEM)及电子探针(EPMA)研究了ZnO压敏陶瓷几种典型添加剂Bi_2O_3,MnO_2,Co_2O_3,Sb_2O_3,Cr_2O_3组成的作用。结果表明:优良的伏安特性是上述添加剂组成共同作用的结果.ZnO晶粒具有本征电子电导,Bi_2O_3,MnO_2,Co_2O_3是受主型添加剂,在晶界俘获电子而发生价态变化。当外界给予足够的能量(如电能)时,被俘获电子脱离束缚状态,宏观上ZnO陶瓷即从高阻态转向低阻态,显示出对电压的“开关”特性(压敏特性)。Sb_2O_3,Cr_2O_3则不是受主型添加剂,Sb_2O_3与ZnO在适当条件下形成Zn_7Sb_2O_(12)立方尖晶石相,Cr_2O_3具有稳定Zn_7Sb_2O_(12)相的功用,Zn_7Sb_2O_(12)相形成抑制受主型杂质在高温下的挥发,对ZnO压敏陶瓷伏安特性起着间接的贡献。

Study on Composition,Microstructure and Voltage-Current Nonlinear Characteristics of ZnO Varistor Ceramics

The function of several typical additives Bi2O3, MnO2,Co2O3, Sb2O3 and Cr2O3 in ZnO varistor ceramics has been studied by means of Electron Spin Resonance (ESR),X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Electron Probe Microscopic Analyzer (EPMA) techniques. The experimental results show that ZnO varistor ceramics with excellent voltage-current nonlinear characteristics result from the combined effect of those additives. ZnO crystal grain has intrinsic electronic conductance. Bi2O3,MnO2 and Co2O3 as acceptor type additives can capture electrons on the grain boundaries and produce changes in valence. Electrons captured by acceptors can escape the captured state when energy (e. g. electric energy) from outside is high enough. Meanwhile, ZnO ceramics as viewed from macrography change from high-resistance to low-resistance state and present the "switch" characteristics to the voltage (varistor property). Both Sb2O3 and Cr2O3 are not acceptor type additives. Sb2O3 forms with ZnO the spinel phase of Zn7Sb2Ol2 under suitable sintering conditions, which can restrain the acceptors from evaporation at high temperature and contribute indirectly to the voltage-current characteristics. Cr2O3 has the function of stabilizing the Zn7Sb2O12 phase.