Piezoresistivity and the semiconductor-semimetal transition inTi2O3

Abstract

We have measured the effect of stress on the electrical resistivity of single-crystal ${\mathrm{Ti}}_{2}$${\mathrm{O}}_{3}$ using hydrostatic pressure between 270 and 400 K and uniaxial compression between 296 and 500 K in order to study the semiconductor-semimetal transition in this material. Large fractional changes in resistivity per unit stress (piezoresistivities) were found. They are explained as a consequence of Fermi-level motion due to strain changing the gap, or overlap, between conduction and valence bands and thereby the concentration of mobile charge carriers. Extrema in the piezoresistivities, observed near 460 K using uniaxial compression, result from the temperature dependences of the elastic compliances. Simple approximate expressions for the piezoresistivity of statistically degenerate charge carriers scattered by polar optical-mode phonons are compared with our data above 460 K. This yields deformation potentials for the relative motion of the valence and conduction bands whose values are consistent with those deduced from the piezoresistivity of semiconducting ${\mathrm{Ti}}_{2}$${\mathrm{O}}_{3}$ and from elastic-constant data through the transition. The amount of band overlap is much smaller than that used previously to account for elastic constant and specific heat "anomalies" in the temperature range of the semimetal-semiconductor transition, but is consistent with recent reflectance results and analyses of lattice parameter and elastic-constant data.