PREPARATION AND STRUCTURE OF A TERNARY OXIDE OF BARIUM AND RHENIUM, BA3RE2-XO9

Attempts to synthesize BaReO3 resulted in formation of a slightly nonstoichiometric compound with the ideal formula Ba3Re2O9. It was found to have the space group Rm with hexagonal unit cell parameters a=5.7699 (5) Å and c=20.799 (2) Å, Z=3. A total of 2816 reflections were measured on an automatic diffractometer, and the structure was refined by full-matrix least squares on 308 unique reflections to a final R value of 0.027 and Rw of 0.036. It consists of a nine-layer repeat sequence of hexagonal and cubic close-packed layers of composition BaO3. The stacking of these layers along the c axis leads to the formation of two types of octahedral sites, M(1) and M(2), for the Re atoms. An M(2) octahedron shares opposite faces with two M(1) octahedra. Site population analysis has shown that about 8% of the M(2) sites are occupied and that simultaneous occupation of two octahedral sites sharing a face is avoided, resulting in the Re deficient compound Ba3Re1.96O9. All the Ba atoms are 12-coordinated and both ReO6 octahedra show a distortion corresponding to an elongation along the trigonal axis. © 1978, American Chemical Society. All rights reserved.