Journal of Solid State Chemistry 160, 45 } 49 (2001) doi:10.1006/jssc.2001.9182, available online at http://www.idealibrary.com on Preparation, Crystal Structure, and Magnetic Studies of a New Sr 7 Re 4 O 19 Double Oxide and Its Relation to the Structure of Ba 7 Ir 6 O 19 K. G. Bramnik, H. Ehrenberg, and H. Fuess Institute for Materials Science, Darmstadt University of Technology, Petersenstrasse 23,D-64287, Darmstadt, Germany Received November 16, 2000; in revised form March 13, 2001; accepted March 26, 2001; published online May 30, 2001 The complex oxide Sr 7 Re 4 O 19 has been synthesized and its crystal structure was determined by X-ray di4raction powder data analysis (space group C2/m; a  13.6379(3) A  , b  5.6035(2) A  , c  10.3700(3) A  ;   98.348(2)3, Z  2, R I  0.018, R P  0.050). The compound crystallizes in a new structure type, which can be derived from the Ba 7 Ir 6 O 19 structure by removing the Ir atoms from the middle octahedron of three face-sharing IrO 6 octahedra units. This change results in the in5nite cis-bridged chains of the ReO 6 octahedra linked together by common corners. Each chain is connected with another one by the corner-sharing of each second ReO 6 octahedron. The 10- and 12-coordinated Sr atoms are situated between these in5nite structure fragments. Magnetic properties of the Sr 7 Re 4 O 19 com- pound were studied by SQUID measurements.  2001 Academic Press INTRODUCTION In contrary to the other alkali-earth elements, strontium containing ternary rhenium oxides with a rhenium oxida- tion state less than #7 were scarcely investigated. Three di!erent compounds were described in this system. More- over, one of the reported compounds, Sr  ReO  , x"0.4}0.5, was synthesized under extreme conditions such as high pressure and high temperature (50 kbar, 9003C) (1). Its crystal structure based on a three-dimensional network built of corner-sharing Re  O  units. Two other com- pounds were synthesized by a standard ceramic technique, subsolidus reaction of the precursor oxides, SrO and ReO  , at high temperature. The recently reported Sr  Re  O  compound (2) (space group I4  /a) with rhenium in a formal oxidation state of #6.5 can also be considered as a cation- de"cient perovskite-distorted structure. The ReO  oc- tahedra are rotated along the [110] axis by +453, resulting in a distortion of the oxygen environment around the Sr atoms, occupying the other half of the positions in the B-cation sublattice, from an octahedron to an irregular eight-fold polyhedron. The rotation of ReO  octahedra forms two kinds of nonequivalent channels "lled by A- cations. In the "rst one only   of the A positions are occupied by Sr cations with 12-fold and 10-fold coordina- tions. The second one contains Sr atoms surrounded by eight oxygen atoms. Sr  Re  O  shows interesting mag- netic properties and orders ferrimagnetically below 12 K. The complex oxide Sr  Re  O  with a composition similar to Sr  Re  O  has already been reported in the literature (3). Sr  Re  O  was suggested to be isostructural with Ba  Re  O  (4), which has a hexagonal perovskite-like structure based on a 9R(chh)  close-packed stacking of the BaO  layers with Re atoms situated in the octahedral interstices. However the X-ray powder di!raction pattern of the Sr  Re  O  sample was not completely indexed, and its crystal structure was not re"ned. In the present investigation we describe the synthesis, crystal structure, and magnetic properties of the new compound Sr  Re  O  . EXPERIMENTAL SrO and ReO  (STREM Chemicals, 99.9%) oxides were chosen as starting materials. SrO was obtained by the decomposition of SrCO  at 10003C for 24 h in vacuum, 10 mbar. Seven moles of SrO and 4 mol of ReO  were thoroughly mixed, ground in an agate mortar under a dry argon atmosphere, and placed in an alumina crucible to avoid a reaction with the silica tube during annealing. To control the partial oxygen pressure during the synthesis a mixture of metallic Ni and NiO was used. This mixture was placed in another alumina crucible and sealed together with the sample in a silica tube with an 8}10 cm volume at 10 mbar pressure. The raw material was annealed for 24 h at 8003C, which corresponds to a partial oxygen pressure value p(O  )"1.0210 bar, which was estab- lished by the getter mixture of Ni/NiO in the balance state at this temperature. The sample was quenched after the synthesis. X-ray di!raction data for the phase analysis and the crystal structure determination were collected with a STOE STADI/P powder di!ractometer (CoK  radiation, curved Ge monochromator, transmission mode, step 0.023 (2), PSD counter). For structure re"nements the RIETAN-97 45 0022-4596/01 $35.00 Copyright  2001 by Academic Press All rights of reproduction in any form reserved.