V. Rajendran

Characterisation of semiconducting V2O5-Bi2O3-TeO2 glasses through ultrasonic measurements

Tellurite containing vanadate (50−x)V2O5–xBi2O3–50TeO2 glasses with different bismuth (x=0, 5, 10, 15, 20 and 25 wt%) contents have been prepared by rapid quenching method. Ultrasonic velocities (both longitudinal and shear) and attenuation (for longitudinal waves only) measurements have been made using a transducer operated at the fundamental frequency of 5 MHz in the temperature range from 150 to 480 K. The elastic moduli, Debye temperature, and Poisson’s ratio have been obtained both as a function of temperature and Bi2O3 content. The room temperature study on ultrasonic velocities, attenuation, elastic moduli, Poisson’s ratio, Debye temperature and glass transition temperature show the absence of any anomalies with addition of Bi2O3 content. The observed results confirm that the addition of Bi2O3 modifier changes the rigid formula character of TeO2 to a matrix of regular TeO3 and ionic behaviour bonds (NBOs). A monotonic decrease in velocities and elastic moduli, and an increase in attenuation and acoustic loss as a function of temperature in all the glass samples reveal the loose packing structure, which is attributed to the instability of TeO4 trigonal bipyramid units in the network as temperature increases. It is also inferred that the glasses with low Bi2O3 content are more stable than with high Bi2O3 content.

Ultrasonic Investigation on Ferroelectric BaTiO3 Doped 80V2O5—20PbO Oxide Glasses

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 Youngs moduli, Debye temperature, Poissons 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.

Ultrasonic characterisation of ferroelectric BaTiO3 doped lead bismuth oxide semiconducting glasses

Abstract Ferroelectric BaTiO3 doped lead bismuth xPbO–(100−x)Bi2O3–5BaTiO3 semiconducting oxide glasses with different PbO contents (x=20,30,40 and 50 wt%) have been prepared by the rapid quenching method. The ultrasonic velocity and attenuation measurements have been made at room temperature (298 K) at frequencies 2.25–10 MHz. From the measured density and ultrasonic velocity data, elastic moduli, Debye temperature, Poissons ratio and other related physical parameters have been determined. At lower PbO content ( PbO wt %) , a monotonic decrease in velocity, elastic moduli and Debye temperature was noted. A further increase in PbO content ( PbO >40 wt %) lead to an increase in all the above parameters, after showing a minimum at 40 wt% of PbO. In addition, the effect of ultrasonic frequency on velocity and attenuation has also been studied in these glasses. The observed results have been explained in terms of the change in the structure and physical properties of the glass network with change in PbO content.

Temperature and Composition Dependence of the Elastic Properties of Semiconducting (100 – x)V2O5–xPbO Oxide Glasses

Semiconducting vanadate lead glasses with different PbO contents have been prepared by rapid quenching technique. Ultrasonic velocities and attenuation measurements have been performed over a wide range of temperatures from 150-480 K. Elastic moduli, Debye temperature and Poissons ratio have been obtained for different PbO contents as a function of temperature. For a fixed temperature, the composition dependence of velocities and attenuation shows a monotonic variation with the addition of PbO. Nevertheless, the elastic moduli, Debye temperature, and Poissons ratio exhibit anomalies at 33 wt% of PbO. The observed anomalies are discussed in terms of PbO acting as a network modifier or network former depending on the PbO content. In contrast to many other glasses a linear decrease in ultrasonic velocities and elastic moduli as a function of temperature is noticed without any indication of anomalies. These dependencies will be explained in terms of the structural softening taking place in the glasses. The measured acoustic loss and attenuation as a function of temperature show anomalies between 200 and 270 K depending on the PbO content. The anomalies in attenuation have been explained in terms of a thermally activated relaxation process.

Ultrasonic Investigation on Nanocrystalline Barium Borate (BBO) Glass Ceramics

Barium Borate (BBO) glasses containing different compositions of BaO and B2O3 with BaF2, Cr2O3 and TiO2 have been prepared by normal melting and annealing technique. The prepared bulk BBO glasses have been subjected to heat‐treatment. The heat‐treated BBO glasses produce nanophase BBO crystals in its structure. The existence of nanophase structure of the BBO crystals have been studied through XRD and the results reveal that the size of the particles is in the order of less than 100 nm. The SEM studies also support the observed XRD study and it explores the crystalline BBO crystal in the nano range. Further, the ultrasonic velocity, attenuation and their related parameters have been measured before and after heat‐treatment. The observed higher magnitude of variation in the ultrasonic parameters in nanophase glasses when compared with bulk glasses reveals a reduction in the particle size. The present investigation reveals that ultrasonics is one of the best tools to characterise the nanophase materials.

Elastic Properties of and Dependence on Microstructure of Phosphate Based Bioactive Glasses

The technology of bioactive glasses opens up new possibilities in the natural sciences and medicine in view of their use in a variety of emerging new biomedical applications, such as replacement of damaged/diseased body parts. A better understanding of the physical, chemical and mechanical properties of bioactive glasses is required for wider biomedical applications. One can control various properties of bioactive glasses not only by changing their composition but also by subjecting them to different thermal treatments. For the effective bonding of bioactive glass in bone and dental applications, one has to optimise the composition, which requires a complete knowledge of the bone stiffness and mechanical properties. Earlier studies of bioactive glasses reveal their importance in biomedical applications in view of their high bioactivity and high fracture toughness. This is possibly due to the change in microstructural, mechanical and chemical properties of bioactive glasses that result from changes in composition and by varying thermal treatments. As discussed in our earlier studies, even though several techniques, such as static bending and resonance, are available for the evaluation of elastic properties of bioactive glasses, the ultrasonic nondestructive testing (NDT) technique has been found to be more sensitive when exploring the change in elastic and structural properties of bioactive glasses. This is mainly due to the various advantages of the ultrasonic NDT technique in comparison with other techniques, some of which are destructive or semi-destructive. Further, during the ultrasonic testing, the material will not be subjected to any damage. In addition, it is possible to probe into the macro-, microand submicroscopic particles due to the close association of the ultrasonic waves with elastic and inelastic properties of materials, the availability of many modes of vibration and the wide range of frequency selection of the ultrasonic waves. Therefore, in the present investigation, bioactive glasses with and without P2O5 content have been prepared for different compositions to explore 1) the effect of the frequency of the ultrasonic sound velocity and 2) the effect of thermal treatments on the ultrasonic properties in all bioactive glasses. The observed results are discussed in terms of the changes in structure, stability and elastic properties of bioactive glasses.