No abstract

Structural and functional properties of multiferroic BiFeO3 are currently under debate. We utilized Raman spectroscopy to characterize the structural properties of pure and up to 10mol% LaMnO3-doped polycrystalline BiFeO3 thin films. All films were identified as phase-pure perovskite using x-ray diffraction (XRD). Although XRD has insufficient sensitivity for detailed thin film analysis, Raman experiments showed that pure BiFeO3 structure is best described as monoclinic, and that doping with LaMnO3 causes substantial modifications, namely, Jahn–Teller distortions to the (Mn,Fe)3+O6 octahedra accompanied by structural transition toward orthorhombic. Manganese substitution is shown to be the main cause of these changes.

Ternary phosphates are found to vitrify within large domains of compositions inside the phase diagrams P 2 O 5 -WO 3 -A 2 O (A ‫؍‬ Li, Na). Structural approach of the highly modified glasses P 2 O 5 -A 2 MoO 4 -A 2 O (M ‫؍‬ Mo,W) was investigated using various spectroscopic techniques such as infrared, Raman, and electron spin resonance (ESR). These glasses were found to contain MO 6 octahedra, MO 4 tetrahedra, M 2 O 7 dimers, PO 4 tetrahedra, and also P 2 O 7 or metaphosphate chains, depending on the composition considered. As shown in earlier studies, the glass network is progressively depolymerized as the content of A 2 O increases. ESR experiments were conducted on both X-ray irradiated and unirradiated samples. Unirradiated glasses exhibit two ESR signals attributed to W 5؉ and Mo 5؉ centers that are octahedrally coordinated. Irradiation of these glasses induces new paramagnetic centers ascribed to the phosphorus-oxygen-hole-center and peroxy radicals. The M 5؉ concentration depends strongly on the sample composition and temperature. ESR parameters are determined using a computer simulation approach adapted for vitreous materials.

No abstract

No abstract