Study of microstructural behavior and nonadiabatic small polaron hopping conduction in BaTiO3 doped lead-vanadate glass and glass-ceramics dispersed with ferroelectric nanocrystals

Abstract

Multicomponent semiconducting oxide glasses like (80 V2O5–20 PbO)+xBaTiO3 (x=5–30 wt %) dispersed with nanocrystalline BaTiO3 have been prepared by a fast quenching technique. Results of microstructural study and transport properties (between 80 and 450 K) of these glasses and some glass ceramics have been reported in this article. It has been shown from x-ray diffraction, scanning electron microscopic, and other studies that homogeneous glasses are formed with wide concentrations of BaTiO3 (x⩽30 wt %). Transmission electron microscopic study, however, indicates the presence of nanocrystalline phases in the glass matrix. Mott’s variable range (nonadiabatic) hopping conduction mechanism is found to be valid at the low temperature regime (below θD/4, θD being the Debye temperature) while in the high temperature regime (above θD/2), the polaron hopping models of Schnakenberg as well as Emin and co-workers can quantitatively predict the conductivity data for all these special types of multicomponent glass-nanocrystal composites. The model parameters, obtained from best fit of the experimental data with these models, are consistent with the glass compositions. The dielectric constants of these glasses are found to be very high (comparable to that of bulk BaTiO3) and about two orders of magnitude higher than those of BaTiO3 free (80 V2O5–20 PbO) and other transition metal oxide glasses. This novel character is considered to be due to the embedded nanocrystalline BaTiO3 phases. The glass samples annealed at 300 °C for 9 h in air also showed nano and microcrystalline BaTiO3 phase along with traces of PbV2O6, PbTiO3, TiO2, and Pb2V2O7 phases. Broad anomaly (with a maximum around 390 K) is observed from the thermal variation of dielectric constant data of these partially annealed glass-ceramic samples. This anomaly resembles to the anomaly observed around the Curie temperature (∼393 K) in bulk ferroelectric BaTiO3 crystal.