Oxygen adsorption and VDR effect in (Sr, Ca)TiO_3−x based ceramics

The relation between the oxygen adsorption and the voltage dependence of the resistor (VDR effect) in (Sr, Ca)TiO_3−x based ceramics has been investigated. The nonlinearity of the voltage-current characteristics increased with increasing the barrier height, which is thought to be generated by the oxygen chemisorption. Acceptor type trap levels were detected by means of a zero biased DLTS technique at high temperatures. These interfacial energy levels changed with reoxidizing temperatures, and the change can be explained by the degradation of the chernisorbed oxygen. The high temperature type of the chemisorbed oxygen as O²⁻ and O is relatively stable due to the strong pinning effect of trapped electrons, with reoxidizing anneals of grain surfaces above the oxidation temperature, and it contributes greatly to the VDR effect. It is concluded that energy barriers are caused by the interface states generated by the chemisorbed oxygen on grain surfaces and that they determine the VDR effect.