Magnetic resonance study of the v2O5-P 2O5 Semiconducting Glass System

Abstract

The 51V NMR of the diamagnetic V5+ and paramagnetic V4+ ions has been studied in the semiconducting V2O 5-P2O5 glass system. From computer-simulation studies of the 51V NMR experimental spectra due to the V5+ sites, it has been determined that the spectra obtained at the higher spectrometer frequencies can be described by a skewed distribution of powder patterns arising from axially symmetric chemical shifts. The most probable value of the chemical shift distribution (σ||)mp of the chemical shift parameter σ|| decreases with increasing V2O5 content and (σ⊥)mp is independent of glass composition. An estimate of the nuclear quadrupole coupling constant of the V5+ site has been made; it ranges from 1.0 to 1.5 MHz as the V 2O5, content of the glass is increased. The NMR data are interpreted in terms of two types of VO5 units in the glass. One is a VO5 unit similar to that in crystalline V2O5 and the other is a VO5, unit with a PO4 unit substituted for the apex oxygen. From ESR intensity measurements, the ratio of the fractions of V4+ and V5+ ions (n4/n5} present in the glass has been determined as a function of glass composition. There is some evidence to indicate that two V4+ sites are formed for each PO4 unit that is substituted for an apex oxygen of a VO5 unit. The implications of these data for the electrical conductivity of the glasses are discussed.