Structure and physical properties of glassy lead vanadates

The structure and physical properties of the lead-vanadate glasses of compositions (V₂{O}₅)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 V₂{O}₅$ and affected ${VO}₅$ groups. A gradual decrease in the coordination number of ${V}⁵⁺$ and ${V}⁴⁺$ ions and the formation of nonbridging oxygen atoms have been observed with increasing ${V}₂O₅ content in the glass compositions, consistent with the decrease in density. The nearly equimolar glass composition devitrifies to crystalline metavanadate PbV₂{O}₆$. However, glasses with higher ${V}₂O₅ content devitrify to PbV₂{O}₆$ and a ${V}₂O₅-rich amorphous phase. The fine structure of the electron spin resonance hyperfine lines observed when the glass composition is equimolar, gradually reduces to a two-component structure at the same effective g value and is interpreted as due to an increase of the hopping rate of polarons with increasing V₂{O}₅$ content in the glass compositions.