Gaponov A. Electrical properties of varistor tin oxide ceramics

Object of research – phenomenon of electroconductivity and deviation from Ohm’s law in semiconducting tin oxide ceramics. Aim of research – to obtaining new ceramics materials with varistor features in systems SnO2-Co3O4-Nb2O5-Cr2O3-X (X = V2O5, PbO, CuO, CuO-CaO, CuO-SrO, CuO-BaO) and to study their electrophysical characteristics. Methods of research - scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, differential thermal analysis, thermogravimetrical analysis, laser Raman spectroscopy; dependences of current density upon electric field, temperature dependences of dc electrical conductivity, time dependences of capacity while applying direct current, dependences of capacity and ac conductivity upon applied direct voltage have been studied. Tin oxide based varistor ceramics with high non-linear current-voltage characteristic (coefficient of nonlinearity is 75) and low humidity sensitivity have been sintered. Thermally activated mechanism of conductivity at high electric fields has been proved, energy of trap location at grain boundaries has been estimated, activation energy of electrical conduction corresponding to high non-linear CVC area has been estimated. It has been determined that tin oxide ceramics with fusible additive of copper oxide withhold greater density of pulse current than samples sintered without liquid-phase burning. Introduction of CuO additive enabled us to receive SnO2 based ceramics with lower humidity sensitivity and electric parameters stable with time.