Electron diffraction study of inter‐ and intrapolytypic phase transitions in transition metal dichalcogenides. I. Electron diffraction patterns

Structural changes, occurring in the metastable IT modification of TaS₂, have been studied by means of electron diffraction and correlated with changes in the electric and magnetic properties. The IT form was found to adopt a superstructure of the CdI₂ structure at low temperatures and two different distortion modulated structures of the CdI₂ structure at higher temperatures. Close to the transition IT → 2H intense diffuse scattering is observed, which can be related to the occurrence of a Kohn anomaly. The 2H modification which results from the IT modification by a shear transformation, exhibits two superstructures as well. Specimens which have been heat treated in the temperature range where the transition IT → 2H sets in, exhibit the doubly positioned IT superstructure at room temperature. This is attributed to the presence of the 4H_b polytype.