Low-Temperature Specific Heat of Metallic V-DopedTi2O3

Abstract

The specific heat of titanium sesquioxide, ${\mathrm{Ti}}_2$ ${\mathrm{O}}_3$, and the mixed system, ${\mathrm{Ti}}_2{\mathrm{O}}_3+x\%$ ${\mathrm{V}}_2$ ${\mathrm{O}}_3$, with $x$ ranging from 1.9 to 10.3 wt% has been measured between 0.4 and 20 K. The Debye temperature at 0 K for pure ${\mathrm{Ti}}_2$ ${\mathrm{O}}_3$ was found to be 674 K. All the V-doped samples are metallic and exhibit an anomalously large excess heat capacity as compared to that of pure ${\mathrm{Ti}}_2$ ${\mathrm{O}}_3$. At the lowest temperatures the excess specific heat is linear in temperature and can be extrapolated to the origin. At a relatively low temperature, however, the excess specific heat bends over and becomes practically independent of temperature. The exceptionally large linear term found is of the order 50-80 mJ/mole K and is inversely proportional to the ${\mathrm{V}}_2$ ${\mathrm{O}}_3$ content. The behavior of the excess heat capacity is attributed to an anomaly in the electronic density of states. The specific heat calculated for an electron gas with a density of states varying according to $E^{-\frac{1}{2}}$ is in good agreement with the experimental results and gives the right concentration dependence for the linear term in the specific heat. The implications of such a model are discussed.