Crystal structures of the double perovskites Ba2Sr1−xCaxWO6

Crystal structures and phonon modes of Ba(Ca1/2W1/2)O3, Ba(Ca1/2Mo1/2)O3 and Ba(Sr1/2W1/2)O3 complex perovskites investigated by Raman scattering

“…Figure 1 presents the results from XRD analysis for the different materials, in agreement with previously reported data. [12,17,18,21,26] As it can be observed, XRD analysis was unable to distinguish any significant difference between the samples studied in the present work, although the ceramics with Ca appear like a cubic structure (no peak splitting), while Srcontaining materials seem to be pseudo-cubic (peak splitting or broad peaks with shoulders can be visualized). In this respect, it is common to associate the symmetry presented by perovskite-type materials with the so-called 'tolerance factor'.…”

“…According to the results reported in the literature, monoclinic or triclinic structures would be possible for this material. However, the group-theoretical approaches employed in this work were based on the structures and Wyckoff sites reported in the literature, [12,17,21] and the number of predicted Raman-active bands is very different: 12 bands for a monoclinic structure, while 48 modes are expected for the triclinic structure. The results of the present work are in complete agreement with the I2/m monoclinic space group, which, therefore, must be the correct one for the Ba(Sr 1/2 W 1/2 )O 3 ceramic.…”

“…For these materials, a very recent controversy in the literature regarding their crystal structures guided us to investigate the phonon modes through Raman scattering experiments. From the point of view of crystal chemistry, the materials could be divided in two groups: the first one with Ca and W and the second one with Sr and W. Stewart and Rooksby, [13] Filip'ev et al, [14] Liegeois-Duyckaerts and Tarte, [15] Chi and Bauer [16] and, more recently, Fu et al [17] reported a cubic structure with space group Fm3m (O 5 h , No. 225) for the Ba(Ca 1/2 W 1/2 )O 3 ceramic.…”

“…87) for this material. For the Ba(Sr 1/2 W 1/2 )O 3 ceramic, Kovba et al, [19] Cox et al [20] and Fu et al [12,17] proposed a monoclinic structure with space group I2/m (C 3 2h , No.12) at room temperature. In these works, different techniques were employed, albeit of the discrepancies in the values for the lattice parameters and atomic positions.…”

The intermediate tilt systems in the double perovskites Ba1−xSrxCaWO6 and Ba2−xSrxYSbO6

“…In a recent publication [13], we have reported that the intermediate tilt system a − a − a − occurs in the double perovskites Ba 2 Ca 1−x Sr x WO 6 . Since W(VI), as does Nb(V), has the d 0 -electronic configuration, clearly the presence of -bonding cannot simply be invoked to explain the observed rhombohedral R3 structure.…”