Abstract
To understand the roles of the A- and B-cation that determine the intermediate tilt systems in double perovskites, we investigated, using profile analysis of X-ray diffraction data, the structures of the Ba 2− x Sr x BB′O 6 systems with B = Ca and Y and B′ being either a d 0- (W(VI)) or d 10-cation (Sb(V)). Unlike the recently studied Ba 2Ca 1− x Sr x WO 6 and Ba 2 LnSbO 6 ( Ln = lanthanides and Y) systems, in which the intermediate tilt system is a − a − a − (space group R 3 ¯ ), we found the tilt system a 0 a 0 c − (space group I4/ m) occurring in both systems as the intermediate between the cubic F m 3 ¯ m ( a 0 a 0 a 0) and the monoclinic I2/ m ( a 0 b − b −) structures. This observation does not support the idea that local B′–O π-bonding is the force driving the tilting, but points out that the large A-cation is more important in determining which structure is found at a given composition.
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