Preparation, Structure, and Magnetic Studies of a New Sr11Re4O24 Double Oxide

The complex oxide Sr11Re4O24 has been synthesized and its crystal structure was determined by a combination of X-ray powder analysis (space group I41/a; a=11.6779(1) ?, c=16.1488(2) ?; Z=4) and electron diffraction. Refinement of the crystal structure was carried out using neutron powder diffraction data (CHI2=1.85). The compound has a cation-deficient perovskite-related structure where cation vacancies are located at the A-sublattice. Re and Sr atoms occupy B-positions in an ordered "rock-salt" manner. The perovskite framework is strongly distorted due to rotation of ReO6 octahedra, leading to a formation of the eightfold coordination for Sr atoms in B-positions. An ordered arrangement of Re+6 and Re+7 cations is proposed on the basis of different average Re-O distances. The Sr11Re4O24 structure could be considered as a Ca11Re4O24 type of perovskite structure distortion. A magnetic order of Sr11Re4O24 (ferro- or ferrimagnetic) is observed from SQUID measurements (TC=12.0 K). A moment of MU=0.80 MUB is derived from the paramagnetic region (30-200 K) for Re6+.