Electrical Properties ofTi2O3Single Crystals

Abstract

Crystals of ${\mathrm{Ti}}_2$ ${\mathrm{O}}_3$ of relatively high purity or doped with various impurities have been grown by the Czochralski method. The semiconductor-metal transition commenced at 435°K with a change of resistivity from 9×${10}^{-3\mathrm{}}$ to 3×${10}^{-4\mathrm{}}$ Ω cm. The resistivity at 4.2°K varies between 0.02 and 6×${10}^5$ Ω cm, depending on purity and stoichiometry. At 77°K and 273°K, the Hall coefficients are positive, small, and independent of magnetic field. At 4.2°K, reliable values could not be obtained. Magnetoresistance was measured in fields up to 220 kG. At 77°K and above, $\frac{\Delta \rho }{{\rho }_0}$ never exceeds ${10}^{-3\mathrm{}}$. At 4.2°K, $\frac{\Delta \rho }{{\rho }_0}$ for the purest sample rises quadratically with applied magnetic field, reaching a value of about 4 at 220 kG. This result cannot be interpreted in terms of a one-band model. A method has been developed for determining carrier mobilities from magnetoresistance data for an intrinsic semiconductor with mirror-image bands. Application of this method to the data for the purest samples yields carrier mobilities of 500-1000 ${\mathrm{cm}}^2$/V sec at 4.2°K. The various results have been interpreted in terms of an elementary band-structure model which does not invoke antiferromagnetic ordering effects to explain the semiconductor-semimetal transition observed in ${\mathrm{Ti}}_2$ ${\mathrm{O}}_3$.