Strain of interatomic bonds and crystallochemical aspects of AB′1/2B"1/2O3 oxides with perovskite structure

A method for determining the strain characteristics of interatomic bonds in crystals of ternary oxides AB'B-1/2"O-1/2(3) with perovskite structure, i.e., AB'B-1/2"O-1/2(3) (B" = Nb, Ta, Sb, Re, or Bi) and A B-1/2'B-2+(1/2)"6++O-3 (B" = Mo, W, Re, Os, or U), is developed. A linear relationship is established between the effective lengths of unstrained B-O bonds (l(0BO)) and the lengths of unstrained B'-O (l(0B'O)) and B"-O (l(0B"O)) bonds, which differs from the Vegard rule. The found values of l(0B"O) for ternary oxides with perovskite structure turned out to be close to the average interatomic B"-O distances in crystals of polymorphic phases of low-symmetry simple oxides. It is shown that the average length of the unstrained Pb-O bond in Pb B'(1/2)/B"O-1/2(3) perovskites corresponds to the length of the same bond in binary oxides PbBO3. For ternary oxides with perovskite structure, a linear correlation between the bond-strain energy and the temperature of their transition to the cubic phase is established. A linear correlation is found between the ratios of the Curie temperatures and the bond-strain energy for lead niobates and tantalates.