Brendan J. Kennedy and Ismunandar
The influence of thermal annealing on cation disorder in ABi2Nb2O9 (A=Sr, Ba) has been studied using synchrotron powder X-ray diffraction methods. BaBi2Nb2O9 adopts a tetragonal (I41/mmm) structure, whilst SrBi2Nb2O9 is orthorhombic, space group A21am, irrespective of the annealing conditions. In both complexes the A-type cations, Sr and Ba, are disordered over the perovskite and Bi2O2 layers. Quenching the samples from high temperature results in a slight increase in both the cell volume and the degree of disorder, the extent of disorder being greater in the Ba complex. Variable temperature diffraction studies are also reported.