Volkan Kalem

Crystallization Behaviour of some TeO2-ZnO Glasses

Zinc-tellurite glasses, comprising 80 mol% TeO2 20 mol% ZnO (hereafter referred to as 0.8TeO2 – 0.2ZnO) and 60 mol% TeO2 40 mol% ZnO (hereafter referred to as 0.6TeO2 – 0.4ZnO), were crystallized at different temperatures on the basis of DTA analyses. Using XRD, SEM and EDS analyses, the crystallizing phases, with their shapes and sizes, were determined in these glass compositions. Thus, different effects of ZnO content on crystallization of binary zinc-tellurite glasses were studied. It was found that crystallizing phases were different for two different samples. In the 80TeO2 20ZnO glasses, α-TeO2 (paratellurite) crystallizes first at around 428 o C, and Zn2Te3O8 phase crystallizes at around 458 o C. On the other hand, in the 60TeO2 40ZnO glass, only the Zn2Te3O8 phase crystallizes. Since this crystallization takes place at around 432 o C, it can be concluded that increasing the ZnO content in zinc-tellurite glasses slightly increases the crystallization temperature.

Crystallization Behavior of some TeO2-GeO2-ZnO Glasses

Abstract. Crystallization behaviors of 80 mol% TeO2-10 mol% GeO2-10 mol% ZnO, 85 mol% TeO2-5 mol% GeO2-10 mol% ZnO and 90 mol% TeO2-5 mol% GeO2-5 mol% ZnO glasses were investigated by using differential thermal analysis (DTA), scanning electron microscopy (SEM) and X-ray diffraction (XRD). DTA curves in the temperature range from 25 °C to 750 °C with the heating rate of 10 °C/min are used to determine the thermal properties such as glass transition temperature Tg, and crystallization peak temperatures Tp. Glass samples were crystallized in the vicinity of these crystallization peak temperatures. Phase analyses were carried out by XRD and SEM techniques.

Optical Properties and Crystallization Kinetics of TeO2-GeO2-ZnO Glasses

Ultraviolet visible near-infrared (UV/VIS/NIR) and differential thermal analysis (DTA) measurements were carried out in order to investigate the optical and thermal properties of TeO 2- GeO 2-ZnO glasses. The samples were prepared by fusing the mixture of their respective reagent grade powders in a platinum crucible at 850 °C for 1h. According to the DTA scan curves of 0.85TeO 2-0.05GeO 2-0.10ZnO and 0.90TeO 2-0.05GeO 2-0.05ZnO glasses taken at different heating rates, activation energy values and the Avrami constants for the crystallization peaks were determined. The absorption spectra measured between 300 - 800 nm wavelength region were used to determine the optical band-gap and Urbach energies of the glasses.

Effect of Modifier Content on the Crystallization and the Optical Gaps of a TeO2-ZnO Glass

On the basis of DTA analyses, crystallization mechanism and crystallization activation energy of 0.6TeO 2-0.4ZnO glass were determined. Also, the effect of ZnO content on the optical band-gap and Urbach energies of (1-x) TeO 2 - (x)ZnO (where x=0.2, 0.3 and 0.4 in molar ratio) glasses have been examined by ultraviolet- visible- near infrared (UV / VIS / NIR) absorption measurements between 300 - 800 nm wavelength region. It is found that they both are functions of glass composition.

Kinetic Study and Optical Investigations of some TeO 2-GeO 2 Glasses

On the basis of DTA analyses of 0.9TeO 2 - 0.1GeO 2 and 0.8TeO 2 - 0.2GeO 2 glasses, the Avrami parameters were determined to be 3 indicating that the mechanism for the crystallization is bulk crystallization. DTA analyses were carried out at different heating rates and two crystallization peaks were observed for both of the glass compositions. The crystallization activation energies were determined by using the variation of peak temperatures with the heating rate. The absorption spectra measured between 300 - 800 nm wavelength region were used to determine the optical band-gap and Urbach energies of the glasses. It is found that they both are a function of glass composition.

Crystallization Behavior of (1-x)TeO 2- xGeO 2 (x = 0.1 and 0.3 mol.) Glasses

Crystallization behaviors of 0.7TeO 2-0.3GeO 2 and 0.9TeO 2-0.1GeO 2 glasses were studied using DTA, XRD and SEM. Thermal measurements showed that the effect of different GeO 2-contents in these glass system resulted in different crystallizing phases. On the basis of DTA, crystallization experiments of two glass samples were carried out at different temperatures for 10 min. The crystallized phases were identified by X-ray diffraction analysis. In both glasses, crystalline phases formed as a result of bulk crystallization.