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

Abstract

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.

Dielectric properties and scaling behavior of lithium tungsten phosphate glasses

“…Thus It can be assumed that with the addition of WO 3 up to 10 mol% a mixed ionic-electronic conduction mechanisms operation are simultaneously obtained, where formation of ion-polaron pair tend to decrease the conductivity and increase in the ΔE dc values in agreement with observed by [13]. The increase in dc electrical conductivity and decrease in ΔE dc with increasing WO 3 content beyond 10 mol% , could be attributed to that the electronic conduction becomes the predominant one ,where as the increase in W +5 concentration with increasing WO 3 content, increases the electronic conduction [10]. It has also been reported that in some glasses containing both alkali metal cations and transition metal ions, electrical transport is mainly electronic since alkali metal cations have small mobility.…”

“…W + 6 ions act as modifiers, weaken the glass network and ,thus create pathways suitable for migration of free ions that build up space charge. Thus, the weaker the network the much more is the space charge polarization which leads to an increase in the dielectric constants values [10,28]. This conclusion is further supported by the results that with increasing WO 3 content in alkali phosphate glasses, the degree of deformation of glass network will increase bonding defects, which in turn increase the space charge polarization causing an increase in the values of dielectric parameters [7,31].…”

“…This effect designated as the "ion-polaron-effect" or IPE. Boudlish et al [10] reported an increase in W +5 concentration with the addition of Li 2 WO 4 to Li 2 O-Li 2 WO 4 -P 2 O 5 glasses, where the WO 3 content is kept constant. They related such increase to the loss of oxygen during glass preparation and its subsequent stabilization in glass.…”

“…When a glass contains alkali cations and transition metal ions, a mixed electronic and ionic conduction is expected. The conductivity of such glasses as a function of alkali content frequently exhibits a minimum similar to the mixed alkali ions effect [ 10]. Recently, the mixed ionic-electronic conductors glasses have an attracted interest due to their potential applications in electrochemical cells and electro-optical devices [11].…”

Structural Elucidation of Borate Glasses by Spectroscopic and SEM Studies

“…The role of WO3 that induces the well defined band at 943-931cm -1 from BTB-1 to BTB-6 glass system which is assigned to the stretching vibrations of B-O linkages in BO4 tetrahedra overlapping with the stretching vibrations of WO6 units [9]. There is no significant change in position of these bands.…”