Structural Transitions in Titanium-Diselenide
The superlattice formation in TiSe(,2) appears to be due to an interaction between electrons and holes via a soft zone-boundry phonon. When the holes are filled by electrons from excess Ti, or removed by uncrossing the bands with zirconium doping, the superlattice transition is suppressed. When the electrons are removed by doping with vanadium, the transition is also suppressed. In all cases, the point at which the superlattice disappears coincides with the complete removal of one of the carriers. TiS(,2) has only electrons and does not transform, but it does have a diffuse streaking which is suggestive of a tendency toward the instability.
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