Structure and physical properties of glassy lead vanadates

The structure and physical properties of the lead-vanadate glasses of compositions (V2O5)x(PbO)100-x with x=50-90 mol %, prepared by the roller-quenching technique have been studied. It has been shown by x-ray diffraction, scanning electron microscopy, density and oxygen molar volume measurements, etc., that single-phase homogeneous glasses with a random network structure can be obtained in this system. The network structure is built up of unaffected VO5 groups as in crystalline V2O5 and affected VO5 groups. A gradual decrease in the coordination number of V5+ and V4+ ions and the formation of nonbridging oxygen atoms have been observed with increasing V2O5 content in the glass compositions, consistent with the decrease in density. The nearly equimolar glass composition devitrifies to crystalline metavanadate PbV2O6. However, glasses with higher V2O5 content devitrify to PbV2O6 and a V2O5-rich amorphous phase. The fine structure of the electron spin resonance hyperfine lines observed when the glass composition is equimolar, gradually reduces to a two-component structure at the same effective g value and is interpreted as due to an increase of the hopping rate of polarons with increasing V2O5 content in the glass compositions