Structural Phase Transitions in A_2-xSr_xNiWO₆ (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 NiWO 4 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: . Temperature-dependent structural studies have been undertaken for selected samples.