Crystal structures and chemistry of double perovskites Ba2M(II)M′(VI)O6 (M=Ca, Sr, M′=Te, W, U)

The role of Yb3+concentrations on Er3+doped SrLaMgTaO6double perovskite phosphors

“…[13][14][15] Since the energy transfer mechanism between donor and acceptor species has been treated within the framework of the Förster and Dexter approaches, 16,17 it is important to know the symmetry site of the donor and acceptor in the phosphors. In a typical double perovskite structure, both B and B 0 are coordinated by orderly arranged six oxygen atoms.…”

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'.…”

“…In this respect, it is common to associate the symmetry presented by perovskite-type materials with the so-called 'tolerance factor'. [12,23,26] Cubic symmetries are expected for compounds with tolerance factors near the unity.…”

“…It is suggested that the difference in the crystal symmetry is due to tilting in the octahedra (anti-phase or in-phase), which is sometimes difficult to determine or quantify by conventional X-ray, synchrotron or neutron diffraction procedures. [1,12] In this work, the complex perovskites of compositions Ba(Ca 1/2 W 1/2 )O 3 , Ba(Ca 1/2 Mo 1/2 )O 3 and Ba(Sr 1/2 W 1/2 )O 3 were studied. 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.…”

“…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.…”