Synchrotron X-ray Diffraction Study of Double Perovskites Sr2RNbO6 (R=Sm, Gd, Dy, Ho, Y, Tm, and Lu)
Winnie K. Wong-Ng, James A. Kaduk, Shailee P. Diwanji
A series of double-perovskite oxides, Sr2RNbO6 (R= Sm, Gd, Dy, Ho, Y, Tm, and Lu) were synthesized and their crystal structure and powder diffraction reference patterns were determined using the Rietveld analysis technique. 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 Sr2RNbO6 are monoclinic with a space group of P21/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 5.84697(9) Å to 5.78151(4) Å, b from 5.93168(12) Å to 5.81030(3) Å, c from 8.32095(11) Å to 8.19022(6) Å, and V decreases from 288.512 (7) Å3 to 275.128 (2) Å3. In this double perovskite series, the R3+ and Nb5+ 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 R3+. Powder diffraction patterns for these compounds have been submitted to the Powder Diffraction File (PDF).