Data on the electrical, optical, magnetic, and structural properties of ${\mathrm{Ti}}_2$${\mathrm{O}}_3$ are reviewed; the differences between the transition encountered in ${\mathrm{Ti}}_2$${\mathrm{O}}_3$ and ${\mathrm{V}}_2$${\mathrm{O}}_3$ are particularly stressed. Perusal of the available experimental and theoretical work leads to the conclusion that the transition in ${\mathrm{Ti}}_3$${\mathrm{O}}_3$ can be explained without invoking antiferromagnetic ordering. This is of particular relevance in light of recent experimental work which casts serious doubt on the commonly accepted hypothesis that ${\mathrm{Ti}}_2$${\mathrm{O}}_3$ is antiferromagnetic. An alternative interpretation of the transition is offered, according to which a gradual change in the position and width of two close-lying bands results in a change of ${\mathrm{Ti}}_2$${\mathrm{O}}_3$ from a narrow-gap semiconductor to a semimetal. It is pointed out that a simple theory based on this model is in essential accord with the available experimental data, and that it satisfies the requirements imposed by crystal symmetry.

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