Crystallization Behaviour of Some TeO 2 - ZnO Glasses M. L. Öveçoğlu 1 , M. R. Özalp 1 , G. Özen 2 , F. Altın 1 , V. Kalem 1 1 Dept. of Materials Science and Eng., Istanbul Technical University 34469, Istanbul, TURKEY 2 Dept. of Physics, Istanbul Technical University 34469, Istanbul, TURKEY Keywords : Zinc-tellurite glass, crystallization, α-TeO 2 , Zn 2 Te 3 O 8 . Abstract. Zinc-tellurite glasses, comprising 80 mol% TeO 2 - 20 mol% ZnO (hereafter referred to as 0.8TeO 2 – 0.2ZnO) and 60 mol% TeO 2 - 40 mol% ZnO (hereafter referred to as 0.6TeO 2 – 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 80TeO 2 - 20ZnO glasses, α-TeO 2 (paratellurite) crystallizes first at around 428 o C, and Zn 2 Te 3 O 8 phase crystallizes at around 458 o C. On the other hand, in the 60TeO 2 - 40ZnO glass, only the Zn 2 Te 3 O 8 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. Introduction Zinc-tellurite glasses are very stable and can serve as superheavy optical flint glasses [1], and are potential materials for fiber lasers and fiber amplifiers when doped with rare-earth ions [2]. These glasses have been extensively studied with various characterization methods in the recent decades. However, there is a lack of data on the crystallization behavior and kinetics of these glasses in the literature. Such a study is important for a glass laser material, which will bear high thermal loads, and thus will be subject to deformation and crystallization, during laser operation. Experimental Procedure To prepare the glass samples, batches of 5 g were thoroughly mixed and melted in a lidded platinum crucible at 800 o C for 60 minutes. This was done in an electrically heated furnace maintained in air atmosphere. The glass melts were removed from the furnace and then quenched in a stainless steel mould. Differential thermal analysis (DTA) scans of as-cast glass specimens were carried out in a Rigaku Thermoflex thermal analyzer equipped with a PTC-10A temperature control unit in order to determine the glass transition temperatures (T g ), crystallization (T c ) and the peak crystallization temperatures (T p ). Static non-isothermal DTA experiments were performed by heating 12 mg glass powders at heating rates of 5, 10, 15 and 20 o C in a Pt-crucible and using the same amount of alumina powder as the reference material in the temperature range between 15 and 700 o C. Scanning electron microscopy (SEM) investigations were conducted in a JEOL™ Model JSM-T330 operated at 20 kV and linked with a Zmax 30 Boron-up light element energy dispersive spectrometer (EDS) detector. The X-ray diffraction analysis were carried out in a Phillips™ Model PW3710 using CuKα radiation at 40 kV and 40 mA settings in the 2θ range from 10 to 90 o . Key Engineering Materials Vols. 264-268 (2004) pp 1891-1894 Online available since 2004/May/15 at www.scientific.net © (2004) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/KEM.264-268.1891 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 144.122.172.83-11/11/10,10:09:58)