Ab initio structure determination of new rare earth fluoride borates Ln3(BO3)2F3 (Ln = Sm, Eu, and Gd)

The crystal structures of Ln(3)(BO3)(2)F-3 (Ln = Sm, Eu, and Gd) are determined ab initio from X-ray powder data. The unit cell is monoclinic, space group C2/c, Z = 4, with a = 12.534(1) Angstrom, b = 6.237(1) Angstrom, c = 8.360(1) Angstrom, beta = 97.404(6)degrees, V = 648.1(2) Angstrom(3) for Gd-3(BO3)(2)F-3. The Rietveld refinement reliability converged to R-p = 0.121, R-wp = 0,147, R-exp = 0.050, chi(2) = 8.75. The structure presents a 3D network of Archimedian monocapped antiprisms Gd(1)O4F5 and Gd(2)O7F2. These polyhedra form trimeric entities Gd3O12F9, which build infinite layers parallel to the (010) plane. (C) 1998 Academic Press.