マグネタイトの異方性温度因子の温度と組成に対する依存性 Change in Anisotropic Temperature Factors in Magnetite with Temperature and Cation Deficit
Anomalous change of the mean square displacements (m.s.d.'s) of the octahedral site (<I>B</I> site) cation in magnetite (Fe<SUB>3</SUB>O<SUB>4</SUB>) was investigated by means of single crystal X-ray diffraction method and discussed with respect to an electron-phonon interaction.<BR>With change of temperature and cation deficit, m.s.d.'s of the <I>B</I> site cation of magnetite show unique trends. At lower temperatures the <I>B</I> site cation prefers to vibrate along , but this preference is reduced with temperature rise up to 630 K, above which the mean square displacement normal to  becomes dominant. This preference at lower temperature is also reduced with increasing cation deficit, in other words decreasing carrier population in the <I>B</I>-sublattice. In the MPMS measurements weakening of the electron-phonon interaction in the cation deficit one is apparently shown. From this point of view, these characteristic trends suggest relationship between the anisotropic temperature factor, particularly at lower temperatures, for the <I>B</I> site cation and the electron-phonon interaction possibly due to presence of charge carriers in the <I>B</I>-sublattice.<BR>The coordinate of oxygen remains nearly constant at x = 0.2549 (1) below approximately 600 K, but increases with increasing temperature above this temperature. This characteristic behavior of the oxygen coordinate with temperature indicates that the cation disordering over the tetrahedral (<I>A</I>) and octahedral (<I>B</I>) cation sites occurs above 600 K.
日本結晶学会誌 42(2), 160-164, 2000-04-30
The Crystallographic Society of Japan