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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 Ti₃O₅ and the triclinic Magn\'eli phases Ti₄O₇, Ti₅O₉, and Ti₆O₁₁ were studied---with the major effort devoted to Ti₄O₇. The only known property of the Magn\'eli 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 Ti₄O₇ at 149^, followed by a second transition at 125^ 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.
Bartholomew et al. (Sat,) studied this question.