Crystal structures of the double perovskites Ba2Sr1−xCaxWO6

✍ Scribed by W.T. Fu; S. Akerboom; D.J.W. IJdo

• Publisher: Elsevier Science
• Year: 2007
• Tongue: English
• Weight: 334 KB
• Volume: 180
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1016/j.jssc.2007.03.008

✦ Synopsis

Structures of the double perovskites Ba 2 Sr 1Àx Ca x WO 6 have been studied by the profile analysis of X-ray diffraction data. The end members, Ba 2 SrWO 6 and Ba 2 CaWO 6 , have the space group I2/m (tilt system a 0 b À b À ) and Fm3 ¯m (tilt system a 0 a 0 a 0 ), respectively. By increasing the Ca concentration, the monoclinic structure transforms to the cubic one via the rhombohedral R3 ¯phase (tilt system a À a À a À ) instead of the tetragonal I4/m phase (tilt system a 0 a 0 c À ). This observation supports the idea that the rhombohedral structure is favoured by increasing the covalency of the octahedral cations in Ba 2 MM 0 O 6 -type double perovskites, and disagrees with a recent proposal that the formation of the p-bonding, e.g., d 0 -ion, determines the tetragonal symmetry in preference to the rhombohedral one.