Temperature and pressure dependent structural studies of the ordered double perovskites Sr2TbRu1−xIrxO6

High resolution powder diffraction studies are reported for the series of mixed RuIr perovskites Sr2TbRu1−xIrxO6. Using a combination of synchrotron X-ray and neutron powder diffraction precise structures are established for the two end-member oxides, where the Tb oxidation state changes from +3 in the Ru oxide to +4 in the Ir containing oxide. The structures of both oxides are monoclinic. Composition dependent studies show that this valence transition is first order. Variable temperature diffraction show no evidence for any structural or valence state transitions. However, upon application of pressure Sr2TbRu0.3Ir0.7O6 undergoes a valence state transition at low pressures.