Claudia J. Rawn, Dunbar P. Birnie, III, M. A. Bruck, J. H. Enemark and R. S. Roth
Source: J. Materials Research, 13, 187-196, (1998)
 
Abstract: Single crystals of barium samarium titanium oxide Ba_6-3xLn_8+2xTi₁₈O₅₄ (x=0.27) have been synthesized and studied using X-ray diffraction action. Superstructure reflections, which cause a doubling of the cell along the short axis, were taken into account and the refinement was conducted in the orthorhombic space group Pnma. Unit cell parameters from single crystal X-ray diffraction were a=22.289(1), b=7.642(1), and c=12.133(1) A. Refinement on F resulted in R1=5.37% for 1410 F_o>4 sigma with the thermal parameters of the Sm and Ba atoms refined anisotropically and the thermal parameters of the Ti and O atoms refined isotropically. The structure is made up of a network of corner sharing TiO₆^-2 octahedra creating rhombic (perovskite-like) and pentagonal channels. The two pentagonal channels are fully occupied by Ba atoms. The refinement suggests that one rhombic channel is fully occupied by Sm atoms (Sm3/Sm4), one rhombic channel is partially occupied by Sm atoms (100% sm1/86.25% Sm5), and one rhombic channel is shared by Ba/Sm atoms (59.25% Ba3/40.75% Sm2), resulting in a formula of Ba_10.38Sm_17.08Ti₃₆O₁₀₈ with Z=1. The above site occupancies differ from the site occupancies previously reported in the literature for refinements conducted with the short axis approximately equal to 3.8 A.