SECOND-ORDER PHASE TRANSITION IN VS ONE-PHASE REGION

The lattice parameters and the densities of vanadium monosulfide samples have been determined by Guinier x-ray powder diffraction and pycnometry, respectively. The samples spanned the homogeneity range of vanadium monosulfide. The data obtained are consistent with sulfur vacancies in samples for which S/V< 1, and vandium vacancies for samples with S/V>1. The lattice parameters were found to vary continuously through the transition from the MDP structure type to the MnP structure type, indicating that the transition is second order.