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 perovskites in which R-O and Ba-O bonds are under compressive and tensile 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 associated with the energy levels obtained, the paramagnetic susceptibility and its evolution vs temperature is simulated according to the van Vleck formalism. The observed deviation from the Curie-Weiss behavior at 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.