TEMPERATURE-DEPENDENCE OF STRUCTURE PARAMETERS IN NATURAL MAGNETITE -SINGLE-CRYSTAL X-RAY STUDIES FROM 126-K TO 773-K

Structural parameters and their thermal changes in natural magnetite, Fe3O4, have been studied using the single crystal X-ray diffraction me thod in the temperature range 126-773 K. The cell dimensions, oxygen c oordinate and atomic mean square displacements (m.s.d.'s) reversibly c hange as a function of temperature. The coordinate of oxygen remains a lmost constant at x = 0.2549(1) below similar to 600 K, but increases with increasing temperature above this temperature. This characteristi c behavior of the oxygen coordinate with temperature indicates that th e cation disordering over the tetrahedral (ii) and octahedral (B) cati on sites occurs above 600 K. All atomic m.s.d.'s increase monotonously with temperature rise. The m.s.d.'s of the B atom show a unique tempe rature dependence. At lower temperatures the B atom prefers to vibrate along [111], but this preference is reduced with a temperature rise u p to 630 K, above which the m.s.d. normal to [111] becomes dominant.