Raman Scattering Studies of the Ba₂MnWO₆ and Sr₂MnWO₆ Double Perovskites

Abstract

Polycrystalline Ba2MnWO6 (BMW) and Sr2MnWO6 (SMW) samples were studied between 80 and 1200 K by Raman scattering spectroscopy. In the case of BMW (space group Fmm), four Raman active vibrational modes, predicted by factor group analysis, were identified. Raman scattering studies with different wavelengths revealed a resonant bands between 300 and 800 cm-1. The origin of these bands was related to the Franck-Condon process. Line broadening versus temperature and phonon frequency were studied, and a qualitative explanation was proposed. SMW samples had considerably more complex Raman spectra. It was found that SMW transformed from tetragonal (room-temperature space group P42/n) to the cubic phase between 670 and 690 K; the phase transition temperature was dependent on sample preparation conditions, and it was considerably lower than in the case of large grain size powders. The role of grain size in phase transition is discussed. Mn ions were found to have a crucial role in the lattice dynamics of both materials.

Raman and infrared spectroscopy of Sr2B′UO6 (B′ = Ni; Co) double perovskites

“…This is opposite to the conventional behavior for the Raman cross sections of higher-order phonons, which are expected to decrease on cooling due to the reduction of thermal disorder. We should mention that strong high-order phonons have been previously observed in other perovskite and double perovskite A c c e p t e d M a n u s c r i p t 6 structures, being generally ascribed to Franck-Condon excitations [21][22][23]. Further study is necessary to verify whether this explanation is also applicable for the compounds studied here.…”

Crystal structure of Ba2InTaO6 as determined by the Rietveld refinement

“…However, it is site sensitive, and thus a suitable probe for local structure and lattice dynamics. Often, Raman spectrum shows additional lines than those calculated from the factor group analysis which may be due to various reasons such as impurity phases [20], second-order Raman scattering [21], electronic transition [22], etc. It is unclear what the additional Raman lines observed in Ba 2 InTaO 6 may signify [6].…”

Electrochemical and Operando Spectroscopic Studies of Sr2Fe1.5Mo0.5O6‐δ Anode Catalysts in Solid Oxide Fuel Cells Operating with Direct Alcohol Fuels

“…This peak is assigned to the A g stretching vibration of the "B" site metals and their surrounding oxygen atoms. [37,38] A noteworthy finding is the absence of any feature near 880 cm À1 corresponding to SrMoO 4 , a major impurity for this material. [39] At 800 8C the SFMO feature has broadened considerably, but is still the dominant feature in the spectrum, Figure 4b.…”

“…Prior to heating the SOFC to 800 °C, an extended Raman spectrum was taken at 25 °C, Figure a, and showed a sharp prominent peak at 802 cm −1 . This peak is assigned to the A g stretching vibration of the “B” site metals and their surrounding oxygen atoms ,. A noteworthy finding is the absence of any feature near 880 cm −1 corresponding to SrMoO 4 , a major impurity for this material .…”