SYNTHESES, STRUCTURES, AND MAGNETISM OF BARIUM/RARE-EARTH/BISMUTH DOUBLE PEROVSKITES - CRYSTAL-STRUCTURES OF BA(2)MBIO(6) (M=CE, PR, ND, TB, YB) BY POWDER NEUTRON-DIFFRACTION

The series of double perovskites Ba(2)MBiO(6) (M = Ce to Lu) have been synthesized and characterized by chemical analysis and powder X-ray diffraction. The crystal structures of Ba(2)MBiO(6) (M = Ce, Pr, Nd, Tb, Yb) have been determined by Rietveld analysis of powder neutron diffraction data. Magnetic susceptibility data for the compounds with M = Ce, Pr, Nd, and Tb are reported. In Ba2CeBiO6, the octahedral B cations are disordered, and magnetic susceptibility data indicate that cerium is present solely as Ce-IV in this phase. Crystal data: M(r) = 719.78, orthorhombic, Pbnm (No. 62), a = 6.2158 (3) Angstrom, b = 6.1793 (3) Angstrom, c = 8.7286 (4) Angstrom, V = 335.25 (3) Angstrom(3), Z = 2, R(p) = 6.92%, R(wp) = 8.64%, chi(2) = 1.22. Ba2PrBiO6 shows similar to 75% ordering of the Pr-III/Pr-IV and Bi-III/Bi-V cations over two sites. This phase shows temperature-independent paramagnetism. Crystal data: M(r) = 718.03, monoclinic, I2/m (No. 12), a = 6.2011 (2) Angstrom, b = 6.1583 (2) Angstrom, c = 8.6968 (3) Angstrom, beta = 89.922 (5)degrees, V = 332.12 (2) Angstrom(3), Z = 2, R(p) = 7.870/0, R(wp) = 10.04%, chi(2) = 1.13. Ba2NdBiO6 contains fully ordered Nd-III and Bi-V and is paramagnetic between 4.2 and 300 K. Crystal data: M(r) = 723.90, monoclinic, I2/m (No. 12), a = 6.1776 (2) Angstrom, b = 6.1366 (2) Angstrom, c = 8.6686 (3) Angstrom, beta = 89.801 (2)degrees, V = 328.62 (3) Angstrom(3), Z = 2, R(p) = 3.12%, R(wp) = 4.34%, chi(2) = 1.28. Paramagnet Ba2TbBiO6 contains a mixture of Tb-III and Tb-IV at the terbium site and Bi-III and Bi-V at the bismuth site. Crystal data: M(r) = 738.58, monoclinic, I2/m (No. 12), a = 6.1104 (2) Angstrom, b = 6.0813 (3) Angstrom, c = 8.5922 (4) Angstrom, beta = 89.97 (2)(d)egrees, V = 319.28 (2) Angstrom(3), Z = 2, R(p) = 6.76%, R(wp) = 8.52%, chi(2) = 1.06. Ba2YbBiO6 contains Yb-III on one octahedral site and Bi-V on the other. Crystal data: M(r) = 752.69, trigonal R (3) over bar (No. 148), a = 6.0252 (2) Angstrom, alpha = 60.037 (2)degrees, V = 154.797 (1) Angstrom(3), Z = 1, R(p) = 4.71%, R(wp) = 5.90%, chi(2) = 1.87.