Spectroscopic and dielectric investigations of tungsten ions doped zinc bismuth phosphate glass-ceramics

Pure and tungsten oxide doped ZnF2Bi2O3P2O5 glass-ceramics are prepared by the melt quenching and heat treatment techniques. These samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS) and differential thermal analysis (DTA) techniques. The X-ray diffraction and the scanning electron microscopic studies have revealed the presence of BiPO4, α-Zn3(PO4)2, α-Zn(PO3)2, Zn3(PO4)2, WOF4, WOPO4, γ-Bi2WO6, Bi2W2O9, microcrystalline phases in these samples. FTIR and Raman studies exhibit bands due WO4 and WO6 units along with conventional phosphate groups. The optical absorption and electron spin resonance (ESR) spectra of present glass-ceramics indicate the co-existence of both W5+ and W6+ ions. The analysis of dielectric properties (dielectric constant, loss tan δ, a.c. conductivity) over a range of frequency and temperature suggests a gradual increase in semi conducting character with increase in the concentration of WO3. The studies on dielectric breakdown strength indicated the lowest insulating strength for 5.0 mol% of WO3 in the present samples.