Synchrotron X-ray diffraction study of double perovskites Sr 2 R NbO 6 ( R = Sm, Gd, Dy, Ho, Y, Tm, and Lu)

A series of double-perovskite oxides, Sr 2 R NbO 6 ( R = Sm, Gd, Dy, Ho, Y, Tm, and Lu) were prepared and their crystal structure and powder diffraction reference patterns were determined using the Rietveld analysis technique. The crystal structure of each of the Sr 2 R NbO 6 phase is reported in this paper. The R = Gd, Ho, and Lu samples were studied using synchrotron radiation, while R = Sm, Dy, Y, and Tm samples were studied using laboratory X-ray diffraction. Members of Sr 2 R NbO 6 are monoclinic with a space group of P 2 1 / n and are isostructural with each other. Following the trend of “lanthanide contraction”, from R = Sm to Lu, the lattice parameters “ a ” of these compounds decreases from 5.84672(10) to 5.78100(3) Å, b from 5.93192(13) to 5.80977(3) Å, c from 8.3142(2) to 8.18957(5) Å, and V decreases from 288.355(11) to 275.057(2) Å 3 . In this double-perovskite series, the R 3+ and Nb 5+ ions are structurally ordered. The average Nb–O bond length is nearly constant, while the average R –O bond length decreases with the decreasing ionic radius of R 3+ . Powder diffraction patterns for these compounds have been submitted to the Powder Diffraction File (PDF).