A COMBINED TIME-OF-FLIGHT POWDER NEUTRON AND POWDER X-RAY-DIFFRACTIONSTUDY OF TERNARY CHROMIUM SULFIDES, VXCR3-XS4 LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-1.0)

A combination of time-of-flight powder neutron diffraction and powder X-ray diffraction has been used to investigate the distribution of van adium and chromium cations between two crystallographic sites in the s eries of ternary sulfides VxCr3-xS4 (0.0 less than or equal to x less than or equal to 1.0). These materials adopt the Cr3S4 structure (spac e group I2/m: a approximate to 5.9, b approximate to 3.4, c approximat e to 11.2 Angstrom; beta approximate to 91.4 degrees) over the entire composition range. However, a marked change in the distribution of cat ions takes place in a region of composition in which anomalies have pr eviously been observed in plots of cell parameters as a function of co mposition. Above x approximate to 0.4, vanadium is almost equally appo rtioned between sites ina fully occupied cation layer and sites in an ordered vacancy layer, whereas at a composition V0.2Cr2.8S4, vanadium preferentially occupies sites in the ordered vacancy layer.