Czochralski Crystal Growth of Zinc Oxide-Tellurium Oxide System
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Czochralski Crystal Growth of Zinc Oxide-Tellurium Oxide System Jalal M. Nawash, Kelvin G. Lynn Center for Materials Research, Materials Science Program, Washington State University, Pullman, WA 99164, U.S.A ABSTRACT Czochralski technique was employed in an attempt to grow a single crystal of the system ZnO-TeO2. A good quality grown crystal is expected to be transparent with a very light yellow color. The crystals exhibit a high resistivity of the order of 1013 Ohm-cm. Different mole percentages have been tested for growth. Several attempts were performed to pull a single crystal. It was found that the best mole percentage of ZnO-TeO2 is 35.5:64.5. The pulled material grows uniformly, such that necking and conning are noticed. The pulled material contained multiple single crystals which were isolated and studied. Each one of them was transparent. Some properties will be presented. The pulled material of the 40:60 ZnO-TeO2 mole percentage returned four phases. Two of these phases are very uncommon.
INTRODUCTION Czochralski (CZ) technique is being used commercially to grow large boules of single crystals. Semiconductor crystals such as Silicon [1] and Germanium [2], as well as oxide crystals [3,4,5] are best grown by CZ technique. Many other types of crystals were also grown by this method [6,7,8]. ZnO has attracted some attention for its useful properties, since it has a wide band gap width of 3.37 eV. This makes the crystal a good candidate for applications in optoelectronic devices such as short wavelength lasers and light emitting diodes (LEDs) [9]. On the other hand, Paratellurite (TeO2) crystals have useful applications in acousto-optic devices [10,11], many of which are used in data display devices (DDD) [12]. The study of this system as a crystal was not examined in literature. A quick investigation of the crystal structure and phase formation was done by some authors [13,14,15,16]. Unfortunately, these studies came because these authors were studying the glass form of the material, not that they were interested in the crystal form of this system. EXPERIMENTAL DETAILS Grade 5 ZnO and TeO2 powders from Alpha Aesar were mixed in certain mole percentages. The most frequent mole percentages that were tested for growth are (in ZnO%:TeO2% order): 21:79, 35.5:64.5, 40:60. The last mole percentage was chosen because it was thought that it will form Zn2Te3O8 stoichiometric compound. The first one came later when a phase diagram was found [13,16]. In this phase diagram, the 21:79 mole percentage goes through a eutectic transform at the lowest melting temperature (~600o C). This has the benefit of reducing the evaporation of TeO2 to its lowest level during the melting phase. The two powders were mixed together using a jar mill from Stoneware. The total average milling time is about 15 hrs. Grinding zerconia beads were used to enhance mixing and milling, this helped bring the sizes of the two powders within close dimension to enhance the reaction
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between them. The mixed powder was place
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