Electrical Properties of Some Titanium Oxides

Electrical conductivity, differential thermal analysis, ac Hall effect, and x-ray diffraction measurements were used to investigate the low-temperature behavior of flux-grown single crystals of the titanium oxides. Monoclinic ${\mathrm{Ti}}_3$ ${\mathrm{O}}_5$ and the triclinic Magnéli phases ${\mathrm{Ti}}_4$ ${\mathrm{O}}_7$, ${\mathrm{Ti}}_5$ ${\mathrm{O}}_9$, and ${\mathrm{Ti}}_6$ ${\mathrm{O}}_{11}$ were studied—with the major effort devoted to ${\mathrm{Ti}}_4$ ${\mathrm{O}}_7$. The only known property of the Magnéli phases was the magnetic susceptibility, which was measured on polycrystalline samples. Several transitions, most of which correlate with previously reported magnetic susceptibility data, were found in these compounds. A semiconductor-to-metal transition occurs in ${\mathrm{Ti}}_4$ ${\mathrm{O}}_7$ at 149°K, followed by a second transition at 125°K which involves some structural rearrangement. The properties of these compounds are discussed in relation to existing theories for the transition-metal oxides. It is concluded that the observed properties are not adequately explained by these theories.