Synthesis and structural characterization of the new rare-earth borosilicates Pr3BSi2O10 and Tb3BSi2O10

Abstract

Abstract The rare-earth borosilicates RE 3BSi2O10 (RE = Pr, Tb) were synthesized under high-temperature conditions of 1600 °C in a radio frequency furnace from praseodymium oxide, terbium oxide, silicon dioxide, silicon nitride, boron trioxide, and boric acid. The structure determinations based on powder diffraction data revealed that both phases RE 3BSi2O10 (RE = Pr, Tb) are isotypic to Gd3BSi2O10 [L. Chi, H. Chen, X. Lin, H. Zhuang, J. Huang, Jiegou Huaxue 1998, 17, 297]. The compounds crystallize in the orthorhombic space group Pbca (no. 61) with eight formula units and the lattice parameters a = 982.9(2), b = 714.2(2), c = 2314.4(4) pm, V = 1.6247(4) nm3, R p = 0.0231, and R wp = 0.0354 (all data) for Pr3BSi2O10 and a = 960.5(5), b = 692.1(3), c = 2272.4(1) pm, V = 1.5106(2) nm3 for Tb3BSi2O10. The lattice parameters of Tb3BSi2O10 could be determined, but a final refinement of the powder data has not proved satisfactory. The structure of Pr3BSi2O10 exhibits eight- (Pr1) and ninefold coordinated rare-earth cations (Pr2 and 3). Layers of ortho-silicate anions [SiO4]4– and borosilicate anions [BSiO6]5– are arranged alternatingly along the c axis and the RE cations are located in between.