ON CHARACTERIZATION OF BARIUM RARE-EARTH ANTIMONATES - ORDERED PEROVSKITES SUITABLE AS SUBSTRATES FOR SUPERCONDUCTING FILMS

The crystal structure of the ordered perovskites Ba-2(RSb)O-6 (R = Y, Ho) is refined from neutron powder diffraction data in the space group Fm (3) over bar m (No. 225), Z=4, with Ba at 8(c), R at 4(b), Sb at 4 (a), oxygen at 24(e), oxygen positional parameter x=0.2636(2) for R=Y and Ho, and unit cell dimensions of a/Angstrom 8.4240(3) and 8.4170(2) for R=Y and Ho, respectively, Bond-valence analysis explains how the highly covalent Sb-O bonds determine the overall structure of these pe rovskites in which R-O and Ba-O bonds are under compressive and tensil e stresses, respectively. The magnetic susceptibility of Ba-2(HoSb)O-6 has been measured in the temperature range 2-350 K. From an a priori estimation of the crystal-field parameters corresponding to the point site symmetry of the rare-earth, O-h, and using the wavefunctions asso ciated with the energy levels obtained, the paramagnetic susceptibilit y and its evolution vs temperature is simulated according to the van V leck formalism. The observed deviation from the Curie-Weiss behavior a t low temperature, very well reproduced, reflects the splitting of the ground state of this cation under the influence of the crystal field. (C) 1997 Academic Press.