Semimetallic character of TiSe₂and semiconductor character of TiS₂under pressure

Presents room-temperature measurements of the in-plane resistivity (j,E perpendicular to c) and Hall coefficient (j perpendicular to c ,B/sub //c/) of TiSe 2 and TiS 2 as a function of pressure. With pressure both the resistivity and Hall coefficient decrease rapidly in TiSe 2 ; this the authors interpret in terms of a changing p-d band overlap, and is consistent with the semimetallic picture for this material. In contrast, the Hall coefficient of TiS 2 is completely independent of pressure, indicating that the carriers present do not arise from this p-d band overlap, but rather from partial occupation of the band as a result of slight Ti excess. Thus the extrinsic semiconductor picture for TiS 2 is favoured by the authors.