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.

Infrared, Raman, and Electron Spin Resonance Studies of Vitreous Alkaline Tungsten Phosphates and Related Glasses

Investigations of molybdenum redox phenomenon in Li2O–MoO3–P2O5 phosphate glasses

Summary It is known that W 5+ , Mo 5+ , and Fe 3+ ions are sensitive indicators for the structural changes of the local symmetry in oxide glasses. Thus, these centres were used as EPR probes in P 2 O 5 -A 2 MO 4 -A 2 O (M=Mo, W and A=Li, Na). The M 3+ ions are located in a distorted environment. Their symmetry is lowered as A 2 O content is high. In iron-dopped glasses Fe 3+ centres occupy distorted octahedra. The distortion extent is less than 7%. Radiation-induced defects have been detected, it is concerned with a PO 4 2− centre and peroxy radicals.

M. El Haddad

Papers

Structural Approach of Glasses Belonging to the Li2O-Li2WO4-P2O5 Ternary System