X-ray reference patterns and structure of the perovskite-related phase R2Cu9Ti12O36 (R=lanthanides)

Abstract

The X-ray Rietveld refinement technique was used to determine the structure and prepare X-ray powder reference patterns for the phases R2Cu9Ti12O36 (R=Nd, Sm, Eu, Gd, Dy, Ho, Y, Er, Tm, Yb, and Lu). R2Cu9Ti12O36 belongs to the perovskite-related [AC3](B4)O12 family of structures, which are cubic with space group Im3. The lattice parameters of the R2Cu9Ti12O36 series range from a=7.377 57(2) Å, V=401.550(3) Å3 for R=Lu to a=7.399 87(3) Å, and V=405.202(4) Å3 for R=Nd. The trend of these lattice parameters parallels the “lanthanide contraction.” In the structure, R occupies the larger icosahedral A site of the ideal ABO3 perovskite structure, while Ti occupies the distorted octahedral B site. The Jahn-Teller cation Cu occupies the C site. The twelve oxygens surrounding Cu are arranged as three mutually perpendicular rectangles of different size. The smallest and largest rectangles are nearly squares. One-third of the R site is vacant, and the chemical formula can be written as [R2∕3X1∕3Cu3](Ti4)O12, where X=vacancy. The X-ray powder patterns of R2Cu2Ti12O36 have been submitted to ICDD for inclusion in the Powder Diffraction File (PDF).