Thermoelectric Effects in Pure and V-DopedTi2O3Single Crystals

Abstract

The Seebeck coefficient $\alpha$ for pure and V-doped ${\mathrm{Ti}}_2$ ${\mathrm{O}}_3$ single crystals has been measured between 54 and 500 K. A very strong peak in $\alpha$ near 75 K for ${\mathrm{Ti}}_2$ ${\mathrm{O}}_3$ is interpreted as arising from phonon-drag effects; this peak is missing for the V-doped specimens. Between 150 and 350 K the variation of $\alpha$ with temperature $T$ could be interpreted in terms of a standard model for mixed conduction in a semiconductor. For $T>\mathrm{}350\mathrm{}$ K, $\alpha$ diminished rapidly with increasing $T$, which reflects the semiconductor-semimetal transition that has been reported in the literature on the basis of conductivity studies. The effect of doping on thermoelectric phenomena has been investigated in detail and is found closely to parallel the effects encountered in conductivity measurements. An explanation is offered as to why V-doped ${\mathrm{Ti}}_2$ ${\mathrm{O}}_3$ exhibits $p$-type characteristics. Values of relevant band parameters have been determined.