Structure and physical properties of glassy lead vanadates.

Abstract

The structure and physical properties of the lead-vanadate glasses of compositions (${\mathrm{V}}_{2}$${\mathrm{O}}_{5}$${)}_{\mathit{x}}$(PbO${)}_{100\mathrm{\ensuremath{-}}\mathit{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 ${\mathrm{VO}}_{5}$ groups as in crystalline ${\mathrm{V}}_{2}$${\mathrm{O}}_{5}$ and affected ${\mathrm{VO}}_{5}$ groups. A gradual decrease in the coordination number of ${\mathrm{V}}^{5+}$ and ${\mathrm{V}}^{4+}$ ions and the formation of nonbridging oxygen atoms have been observed with increasing ${\mathrm{V}}_{2}$${\mathrm{O}}_{5}$ content in the glass compositions, consistent with the decrease in density. The nearly equimolar glass composition devitrifies to crystalline metavanadate ${\mathrm{PbV}}_{2}$${\mathrm{O}}_{6}$. However, glasses with higher ${\mathrm{V}}_{2}$${\mathrm{O}}_{5}$ content devitrify to ${\mathrm{PbV}}_{2}$${\mathrm{O}}_{6}$ and a ${\mathrm{V}}_{2}$${\mathrm{O}}_{5}$-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 ${\mathrm{V}}_{2}$${\mathrm{O}}_{5}$ content in the glass compositions.