Structural phase transitions in A2-xSrxNiWO6 (A = Ca or Ba, 0 ≤ x ≤ 2) double perovskites

Twenty-seven samples in the series of mixed double perovskites of the type A(2)NiWO(6) where A is a suitable alkaline earth cation or combination of such cations (Ca, Ca with Sr, Sr, Sr with Ba, or Ba) have been prepared using NiWO4 as a starting material. The structures of the oxides have been determined using synchrotron X-ray powder diffraction methods, with additional neutron patterns being collected for a smaller number of samples. These studies demonstrated the symmetry increases with the average size of the A-site cation (r(A)) as follows: P2(1)/n <(rA=1.430 angstrom)under right arrow> I4/m <(rA=1.480 angstrom)under right arrow> Fm (3) over barm. Temperature-dependent structural studies have been undertaken for selected samples.