Crystal Growth and Structure of AlSr2YCu2O7

✍ Scribed by P. Bordet; F. Licci; C. Bougerol-Chaillout; M. Marezio

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 198 KB
• Volume: 149
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1999.8525

✦ Synopsis

Millimeter-size crystals of AlSr 2 YCu 2 O 7 were synthesized by the 6ux method in alumina crucibles. Di4erent mixtures of SrO : CuO (ranging from 25 : 75 to 12 : 88 mol ratio) were used as 6ux. No aluminum was added to the reagents. Depending on the 6ux composition and cooling rate, crystals di4erent in morphology and size were obtained. The crystals appear to be tetragonal, space group P4/mmm. However, electron di4raction photographs, in agreement with Ram12 rez-Castellanos et al. (1), reveal that the symmetry is othorhombic with a cell a ‫؍‬ 2a t , b ‫؍‬ 4a t , and c ‫؍‬ 2c t (the subscript t refers to the YBCO tetragonal cell). The structural re5nement was based on X-ray data collected with a KCCD Nonius di4ractometer equipped with a graphite monochromator and AgK radiation. One hundred and ninety-seven independent re6ections with respect to the space symmetry quoted above, with I > 3 , were used. The arrangement is that of a YBCO structure in which the chain Cu cations have been replaced by Al. This substitution induces the movement of the oxygen atoms in the basal layer in such a way as to form, together with the apical oxygen atoms, corner-sharing zig-zag chains of oxygen tetrahedra centered around the Al cations and running parallel to the a-axis either tetragonally or orthorhombically. The b-and c-axes are quadrupled and doubled, respectively, because the zig-zag chains are out of phase perpendicularly to these directions. The additional distortion results in the shift of Al to xx0 (x+0.056) from 000, O1 to xxz (x+0.073) from 00z, and O3 to (0.5, y, 0) (y+0.116) from (0.5, 0, 0).