Independent structural and valence state transitions in the cation-ordered double perovskites Ba2-xSrxTbIrO6

摘要

Synchrotron X-ray and neutron powder diffraction were used to investigate the formation, structure and bonding in the double perovskite Ba2-xSrxTbIrO6 solid solutions. The results showed that these oxides all exhibit ordering of the Tb and Ir cations in a double perovskite-type structure. Three distinct structural types differing in symmetry and/or valence states were formed depending on the precise Ba:Sr ratio on the perovskite A site; x <= 0.3 cubic (Fm3m) with Tb4+ and Ir4+; 0.4 <= x <= 1.0 cubic (Fm3m) with Tb3+ and Ir5+ and x >= 1.2 monoclinic (P2(1)) with Tb3+ and Ir5+. The transitions between these appear to be first order in nature. (c) 2005 Elsevier Inc. All rights reserved.