STUDIES OF SPINELS .6. ANTIMONATES M4IIMIIISBVO8, A NEW, LARGE FAMILY OF SPINELS PRESENTING ORDER-DISORDER TRANSITIONS

A new family of complex antimonates MII4MIIISbVO8 has been synthesized and investigated by X-ray diffractometry and ir and Mössbauer spectroscopy. Many of these compounds possess a spinel structure, with a cation distribution which depends on the nature of MII and MIII. When all the tetrahedral sites are occupied by bivalent cations, these spinels MII2[MII2MIIISb]O 8 are cubic, with either a disordered or a 3 : 1 ordered distribution of the octahedral cations. When the trivalent cation is able to go on the tetrahedral sites, the X-ray powder diagram may be either simple cubic (disordered cation distribution) or more complex, with a number of superstructure lines which can be indexed by considering an orthorhombic cell with a {reversed tilde equals} a0 2 1 2; b {reversed tilde equals} 3a; c {reversed tilde equals} a0, possible space group Imma. The cation distribution of this type of phase has not been fully elucidated, but the combined X-ray, ir, and Mössbauer evidence suggests the presence of the trivalent cation on both tetrahedral and octahedral sites, and a 2 : 1 order on both tetrahedral and octahedral sites, namely, (MII4 : MIII2)[MII8 : MIIISb3]O24. © 1979.