Elastic, optical and thermal properties of zinc-lead tellurite glass systems

This thesis presents the comprehensive study on elastic, optical and thermal properties of tellurite glasses, binary lead tellurite (PbO-TeO2) and ternary zinc lead tellurite (PbO-ZnO-TeO2) glass systems prepared using the conventional melt-quenching technique. The physical, structural, elastic, optical and thermal properties of the glasses were investigated using ultrasonic technique, X-ray diffraction (XRD), scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDX), differential scanning calorimetry (DSC), UV-Visible spectroscopy (UV-Vis) and Fourier transform infrared (FTIR) spectroscopy. Density (ρ), molar volume (Vm), oxygen packing density (OPD), refractive index, band gap energy (Eg), average cross-link density (nc), the number of bonds per unit volume (nb) and Poisson’s ratio (σ) values were calculated from the characterizations data obtained for the interpretation of physical, structural and optical properties of the glass system under study. The density measurements were carried out under ambient condition using densitometer (Model: MD- 300S Densimeter) which works on the basis of Archimedes principle. Ultrasonic pulse-echo technique carried out at room temperature, and resonating frequency of 5 MHz was used for the determination of the ultrasonic velocities (longitudinal and shear). Elastic (longitudinal, shear, bulk and Young’s) moduli, Poisson’s ratio, Debye temperature, and a softening temperature of all glass samples have been calculated using the measured ultrasonic velocities and densities. Experimental values of elastic moduli were compared with calculated values of elastic moduli using bond compression model, Makishima-Mackenzie model, and Rocherulle’s model. The profiles of the EDX analysis showed the presence of all the mentioned elements in the prepared glass system. It is observed from the result obtained that the use of alumina crucible induces a partial dissolution of Al2O3 in the melt that modifies the original composition. The prepared glass samples were homogeneous, lime green color and became more transparent as PbO increases. The XRD pattern confirmed the amorphous nature of the two glass systems. The FTIR spectra for the binary glass system showed a decrease in non-bridging oxygen (NBO) concentration with PbO introduction, which later then increased as more PbO was added to the system. Addition of more ZnO in the ternary system showed a pattern of increasing and decreasing NBO concentration in the glass network. An addition of PbO content in the binary leads to the increase in the density, while molar volume decreased in the tellurite glass system. The density of ternary glass system decrease, and molar volume decreased with the increase of ZnO concentration in the (PbO-ZnO-TeO2) glass system. The elastic moduli of the glasses were found to be composition dependent; the elastic moduli values decreased (from L = 63.41 to 53.55 GPa, G = 21.78 to 16.42 GPa, K = 34.37 to 31.65 GPa, E = 53.94 to 41.99 GPa) for binary tellurite system with increase of PbO concentration and increased (from L = 47.09 to 50.61 GPa, G = 21.78 to 16.42 GPa, K = 27.01 to 28.01 GPa, E = 38.09 to 42.30 GPa) in the case of ternary system increase in ZnO concentration.With the increase in the PbO in the binary system, the microhardness and Debye temperature decreased as the elastic moduli, while the Poisson ratio increased. In the case of the ternary system, increase in the ZnO content increased the microhardness and Debye temperature and decreased the Poisson ratio. . The refractive index of the TeO2-PbO glasses fall in the range of 2.39 to 2.50 for increasing mole fraction of PbO content. The refractive indices for ternary glass system show a varying between 2.504 – 2.580. Thermal analysis of the glasses was realized regarding glass transition temperature (Tg), crystallization temperature (Tc), and glass stability against crystallization (ΔT). The values of Tg, Tc, ΔT and Tm fall in the range of 380 to 311 oC, 379 to 425 oC, 45 to 67 and 469 to 534 oC respectively for the binary glass system and 291 to 300 oC, 389 to 459 oC, 89 – 166 oC and 534 490 oC respectively for the ternary glass system. The two glass systems were observed to be amorphous, with good mechanical strength (on the bases of their elastic properties), thermal stability as well as high refractive index. The high refractive index value index as well as high optical transparency (In the case of ZnO incorporated) for the two series of glasses gives the ternary glass system good potential for optical fiber applications.

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