LATTICE PARAMETER VALUES AND PHASE TRANSITIONS FOR THE Cu2-II-IV-S4(Se4) (II=Mn, Fe, Co; IV=Si, Ge, Sn) MAGNETIC SEMICONDUCTOR COMPOUNDS

X-ray powder diffraction measurements, at 300 K, and differential thermal analysis (DTA) were made on sixteen polycrystalline samples of Cu 2-II-IV-S4(Se 4) (II: Mn, Fe, Co; IV: Si, Ge, Sn) magnetic semiconductor compounds. The diffraction patterns were analyzed to determine lattice parameter values. The results showed that ten have tetragonal stannite 2m 4 I structure, one has tetragonal pseudo-cubic 4 P structure, four an orthorhombic wurtz-stannite Pmn2 1 and two an orthorhombic pseudo-cubic F222 structure. When the values of the effective parameter ae = (V/N) 1/3 are plotted against its molecular weight W, it was found that the tetragonal and orthorhombic materials lie on the same straight line. The peaks on the DTA measurements were used to determine the type of melting as well as the melting temperature. The resulting data together with the Lindemann relation were used to estimate values for the Debye temperature θD as well as for the sound velocity in the material v s.