A study of the crystal structures and the phase transitions of Sr 2 FeSbO 6 , SrCaFeSbO 6 and Ca 2 FeSbO 6 double perovskite oxides A. Faik a, * , J.M. Igartua a , E. Iturbe-Zabalo a , G.J. Cuello a,b a Fisika Aplikatua II Saila, Zientzia eta Teknologia Fakultatea, UPV/EHU, PB 644, 48080 Bilbao, Spain b Ikerbasque and Institut Laue Langevin, BP 156, F-38042 Grenoble, France article info Article history: Received 21 July 2009 Received in revised form 13 October 2009 Accepted 19 October 2009 Available online 23 October 2009 Keywords: Double perovskite X-ray diffraction Neutron diffraction Crystal structure Phase transitions abstract Sr 2 FeSbO 6 , SrCaFeSbO 6 and Ca 2 FeSbO 6 with the double perovskite structure have been synthesized by the conventional solid state reaction process. The crystal structures and phase transitions at low and high temperature were determined from Rietveld refinements of X-ray and neutron powder diffraction data. Sr 2 FeSbO 6 crystallizes at room temperature in a monoclinic system having a space group I2=m and not P2 1 =n space group as was previously reported. The crystal structures of SrCaFeSbO 6 and Ca 2 FeSbO 6 are described with the P2 1 =n space group. All compounds show partial order of the B-site Fe and Sb cations, with degree of ordering of 89% for Sr 2 FeSbO 6 and 94% for SrCaFeSbO 6 and Ca 2 FeSbO 6 . Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction In recent works, we have reported the room-temperature crys- tal structures and the possible phase transitions at low and high temperature of Sr 2 MSbO 6 (M = Al, Co, Cr, Sc, Sm and La) and Ca 2 ScSbO 6 [1–4] members of the antimony double perovskite fam- ily. In the present work we report the synthesis, room-temperature crystal structure determination and phase transitions at low and high temperature of other three members of this family Sr 2 FeSbO 6 , SrCaFeSbO 6 and Ca 2 FeSbO 6 . To the best of our knowledge, no study has been carried out on the possible temperature induced phases transitions, or low- and high-temperature phases of Sr 2 FeSbO 6 , Ca 2 FeSbO 6 and of the new compound SrCaFeSbO 6 . Syntheses of Sr 2 FeSbO 6 have been reported on several occa- sions; in Table 1 we have summarized the available results from previous works to compare with our results. The first preparation of this compound was reported in [5], it was reported to have a cu- bic unit-cell. The room-temperature structure of Sr 2 FeSbO 6 has been reported in serval times [6–9]. According to [6–8], was found to be of an ordered perovskite type, with the monoclinic P2 1 =n space group. however; the authors of [9] did not agree with the previous results and their compound has a ideal perovskite struc- ture with cubic Fm  3m space group. The examination of the re- ported X-ray and neutron powder diffraction profiles, presented in [6–8], did not showed evidence for any reflection corresponding to primitive cell. This was the motivation to re-examine the room- temperature structure of this material, as another member of the antimony family we have been studying during the last years. The synthesis of Ca 2 FeSbO 6 was reported in [5,9,10]. In the first work [5], it was described as an orthorhombic structure, but with- out assigning the space group; and in [10], the structure was de- scribed as monoclinic with the P2 1 =n space group, but the crystal structure was not determined. The crystal structure at room-tem- perature, using X-ray powder diffraction is given in [9]. It was found to be an ordered double perovskite, with the monoclinic P2 1 =n space group. 2. Experimental 2.1. Sample preparation Polycrystalline samples of AFeSbO 6 (A = Sr 2 , SrCa, and Ca 2 ) were prepared by the conventional solid state reaction. Stoichiometric amounts of the reacting compounds were mixed according to the following chemical reaction: ð2  xÞSrCO 3 þ xCaCO 3 þ 1 2 Fe 2 O 3 þ 1 2 Sb 2 O 5 ! Sr 2x Ca x FeSbO 6 þ 2CO 2 ðx ¼ 0; 1; 2Þ: The reacting compounds had the following purities: SrCO 3 (99.995%), CaCO 3 (99.999%), Fe 2 O 3 (99.995%) and Sb 2 O 5 (99.995%). All compounds were used as received from Sigma–Al- drich. The starting materials were mixed and ground in an agate 0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2009.10.027 * Corresponding author. Tel.: +34 695741545; fax: +34 946013500. E-mail address: abdessamad.faik@ehu.es (A. Faik). Journal of Molecular Structure 963 (2010) 145–152 Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc