The frequency dependent ultrasonic velocities (both longitudinal and shear) and attenuation in BaTiO 3 doped (80V 2 O 5 ±20PbO + x BaTiO 3 ) oxide (VPB) glasses (for x 0, 1, 5, 10, and 15 wt% of the base glass) have been measured using pulse echo overlap method at room temperature. From the measured velocity, density and attenuation, various parameters namely longitudinal, shear, bulk, and Young's moduli, Debye temperature, Poisson's ratio, acoustic impedance and microhardness of the VPB glasses were determined. All these parameters of the glasses increase with addition of BaTiO 3 content. On the other hand, attenuation decreases with addition of BaTiO 3 . The variation of these parameters with the addition of BaTiO 3 content was discussed in terms of the change in structure of the glass network. The study reveals that ultrasonic velocity and attenuation measurements have been effectively used as a tool to explore the structural changes and mechanical properties on addition of BaTiO 3 in vanadate lead glasses.
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.
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