Studies of spinels. VI. Antimonates MII4MIIISb VO 8, a new, large family of spinels presenting order-disorder transitions

Abstract

A new family of complex antimonates M II 4 M IIISb VO 8 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 M II and M III. When all the tetrahedral sites are occupied by bivalent cations, these spinels M II 2[ M II 2 M IIISb]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 ⋍ a 0 spinel 2 1 2 ; b ⋍ 3a; c ⋍ a 0 spinel , 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, ( M II 4 : M III 2)[ M II 8 : M IIISb 3]O 24.