Istituto dei materiali per l'elettronica ed il magnetismo     
Beaudry J., Amrate S., Audet N., Mazzera M., Zappettini A. Synthesis of high purity, stoichiometric controlled, TeO2 powders. In: The 16th International Conference on Crystal Growth(ICCG-16) (Beijing, China, 8-13 August 2010).
Paratellurite (TeO2) crystals are largely studied because of their piezoelectric properties and application in acousto-optic devices. Good quality crystals are usually grown by Bridgman or Czochralski techniques, but their final properties strongly depend on the quality of the starting material, both in terms of residual impurities and off-stoichiometry. In this paper, two different approaches for the synthesis of high quality TeO2 starting material have been tested, both using 5N5 Te as precursor. In the first case, basically a pyro-metallurgical method, fine Te powder was subjected to a multi-stage oxidizing process at high temperature (400-650C). In the second case, a hydro-metallurgical method, Te powder was dissolved it in nitric acid, then precipitated. Glow Discharge Mass Spectroscopy shows that both routes produce high purity TeO2 powders: 5N5 purity for the former, 5N purity for the latter. The off-stoichiometry was tested by monitoring the tellurium partial pressure in equilibrium with the samples at high temperatures, according to a method previously developed by some of the authors for other II-VI compounds, such as CdTe, ZnTe, CdS, and CdSe. The measurements show that, while the material produced by the pyro-metallurgical method is always Te-deviated, the material produced by the hydro-metallurgical process has a deviation that is lower then the detection limit of the technique for TeO2, about 0.0005 moles %. The characterization results are discussed taking into account the process parameters. Despite the challenges offered by the hydro-metallurgical process to obtain a high purity oxide, it happens to be the most robust technique to form a highly stoichiometric compound.
Subject TeO2
Stoichiometry measurements

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