Pressure-Temperature Effects on Charge-Transport in Transition-Metal Oxides

摘要

Effects of pressure and temperature on electrical conductivity and thermoelectric power of NiO, CoO, Fe2O3, and Cu2O were measured. The temperature dependence of conductivity and Seebeck coefficient in lithium doped NiO and CoO single crystals indicated that hole mobility was thermally activated with an activation energy of 0.1 ev. Hopping type transport appeared likely in these materials. The temperature dependence of electrical properties on pressure compacted titanium doped Fe2O3 also indicated that electron mobility was thermally activated. Electrical conductivity of Cu2O single crystals increased exponentially with temperature in the 300K to 500K range. The activation energy was 0.26 ev. The Seebeck coefficient was nearly constant, about 1 mv/deg. C from 300K to 500K. Hopping transport is a diffusion process and may have an associated heat of transport. If the heat of transport is not nearly zero, the usual equations for charge concentration and mobility in terms of resistivity and thermoelectric power are not correct. It can be shown that according to the Holstein hopping model the heat of transport should be nearly zero. Conclusions about charge carrier mobility from resistivity and thermoelectric power measurements should be nearly correct. (Author)