Crystal structures and phonon modes of Ba(Ca_1/2W_1/2)O₃, Ba(Ca_1/2Mo_1/2)O₃ and Ba(Sr_1/2W_1/2)O₃ complex perovskites investigated by Raman scattering

Abstract

perovskites by Raman spectroscopy. The samples were produced by conventional solid-state processing at 1200 • C. X-ray diffraction showed that single-phase homogeneous materials were produced, which are cubic or pseudo-cubic in symmetry. The existing controversies in the literature for these complex perovskites were investigated by comparing experimental Raman data with group-theory analysis. Ceramics with Ca and W or Mo were found to be cubic, space group Fm3m. For these materials, four Raman-active bands were observed and the fitting parameters showed that the Ba(Ca 1/2 Mo 1/2 )O 3 ceramic presents bands at lower wavenumbers if compared with the Ba(Ca 1/2 W 1/2 )O 3 sample. For the Ba(Sr 1/2 W 1/2 )O 3 material, two hypotheses were investigated for monoclinic or triclinic structures. The experimental results showed 12 Raman-active modes for this ceramic, which is in perfect agreement with the theoretical predictions for a monoclinic (I2/m) structure.

Recent advances in linear and nonlinear Raman spectroscopy. Part V

“…Dias et al . reported crystal structures and phonon modes of 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 complex perovskites using Raman scattering . The experimental results showed 12 Raman‐active modes for this ceramic, which is in perfect agreement with the theoretical predictions for a monoclinic ( I 2/ m ) structure.…”

Crystal structure of fluorite-related Ln3SbO7 (Ln=La–Dy) ceramics studied by synchrotron X-ray diffraction and Raman scattering

“…In this context, the present paper intends to contribute to the elucidation of the possible crystal structure of Ln 3 SbO 7 ceramics (Ln ¼La-Dy, exception of Ce and Pm), by reporting on our results of Raman scattering, second harmonic generation and synchrotron X-ray powder diffraction (SXRD). A similar methodology was previously applied by our group to solve structural conflicts for many materials [30][31][32][33].…”

Combining Raman spectroscopy and synchrotron X‐ray diffraction to unveil the order types in A3CaNb2O9 (A = Ba, Sr) complex perovskites

“…After a detailed literature revision, [ 18,47 ] we have concluded that the most plausible space group to index the BLCN unit cell is the monoclinic (S.G. #12), being derived from the aristotype cubic phase through an out‐of‐phase tilting as represented by the Glazer system . [ 17 ] Such assumption was also confirmed by the software SPuDS.…”

“…Initial refinements started from the isostructural compound Ba 2 SrWO 6 , [ 49 ] which also has similar Raman distribution with 12 Raman‐active modes at ambient condition. [ 47 ] For BLCN, instead, only nine Raman peaks were used to fit its room condition spectrum in Figure 4b. This perovskite has indeed a pseudo‐cubic crystal structure, [ 50 ] in which Ca 2+ and Nb 5+ ions follow the 1:1 order.…”