Date of this Version
We present the results of Raman scattering measurements on the mixed-crystal systems TiSe2-xSx, TiSe2-xTex, ZrxTi1-x Se2. At room temperature with the pure compounds all have crystal structures represented by the D3d(P3̃m1) space group with three atoms per unit cell. There are two Raman-active k=0 phonons, one of A1gˉ symmetry and one of Eg symmetry. In the TiSe2-xTex system, the A1gˉ and Egˉ phonon frequencies shift smoothly with concentration, and the shifts are well described by a simple virtual-crystal model. The other two systems exhibit a two-mode behavior for which the virtual-crystal model does not correctly predict the observed frequency shifts. A random element isodisplacement model, based on Jaswal’s model for the pure-crystal lattice dynamics of TiSe2 is developed. This model correctly predicts several features of the observed Raman spectra with no adjustable parameters.