Acta Crystallographica Section B

Structural Science

Volume 55, Part 3 (June 1999)

research papers

Acta Cryst. (1999). B55, 348-354 [ doi:10.1107/S0108768198018333 ]

The crystal structure of the B-site ordered complex perovskite Sr(Yb_0.5Nb_0.5)O₃

J. H. Yang, W. K. Choo, J. H. Lee and C. H. Lee

Abstract: The room-temperature crystal structure of the B-site ordered complex perovskite strontium ytterbium niobate, Sr(Yb_0.5Nb_0.5)O₃ [monoclinic, Z = 2, P2₁/n (set 2), a = 5.79095 (8), b = 5.82210 (7), c = 8.20358 (12) Å, [beta] = 90.126 (1)°, with final R_wp = 0.0595, R_Bragg = 0.0203 for the neutron profile and R_wp = 0.0832, R_Bragg = 0.0193 for the X-ray profile, respectively], was determined by X-ray powder diffraction, high-resolution neutron powder diffraction and transmission electron microscopy. This compound shows a slight triclinic distortion from the prototype doubled cubic perovskite cell as a result of an a^-a^-c⁺-type oxygen octahedral tilting distortion. It is also shown that the site ordering of the different species of B-site cations, Yb³⁺ and Nb⁵⁺, inherently leads to a difference between the volumes of the YbO₆ and NbO₆ octahedra. This volume difference is shown to inevitably inhibit the rigid rotation of octahedra.