Perovskite Phases in the Systems AIIO–UVIO3. II. On The System ABIIUVIO6, with AII, BII = Ba, Sr, Ca

Studies on the system A BIIUVIO6 with AII, BII = Ba, Sr, Ca or combinations of these have shown that the alkaline earth ions cannot substitute each other in all proportions. The perovskites were studied by X‐ray diffraction and vibrational spectroscopic methods. The lattice vibration region of the far infrared spectra proved to be of particular value in providing information on the occupancy of the A and B sites. Analysis of the spectra shows that, in the majority of cases, contary to the geometrical predictions some of the larger alkaline earth ions occupy the six‐coordinated B sites and some smaller ions the A positions. The number of ions that take in this A ↔ B site‐exchange can amount to 20%, but in normally smaller.