Synthesis of high purity, stoichiometric controlled, TeO<sub>2</sub> powders

The growth of high quality TeO2 single crystals for acousto-optic devices usually requires a starting powder of relatively high purity (99.995% or better). In addition to foreign metallic impurities, even minute amounts of excess Te precipitating in TeO2 can play a role in the crystal growth behavior and in the resulting properties of the crystal. In this paper, two different approaches for the synthesis of high quality TeO2 starting material have been tested, both using 99.9995% Te as precursor. In the first case, basically a high temperature oxidation process, fine Te powder was subjected to a multi-stage oxidizing process occurring either in vapor or solid phase. In the second case, a hydro-metallurgical method, Te powder was dissolved in nitric acid and then precipitated in form of TeO2. The purity was measured by glow discharge mass spectroscopy and the tellurium fraction in TeO2 was determined by measuring the absorption at 442nm of the gas phase in equilibrium with a solid sample. This technique, used for the first time to measure free Te in TeO2, has proven to apply to this system, leading to good sensitivity and good repeatability. While high temperature oxidation (vapor phase oxidation or solid state diffusion) of 99.9995% Te powder allowed for preserving the purity of the material, the incorporation of impurities was observed when the TeO2 was synthesized through a wet chemical process, leading to a 99.999% purity. This last technique, however, offered the lowest deviation from stoichiometry.

用于声光器件的高质量二氧化碲（TeO₂）单晶的生长通常需要纯度相对较高（99.995%或更高）的起始粉末。除了外来金属杂质外，即使在二氧化碲中析出极少量的过量碲，也会对晶体生长行为以及晶体的最终性能产生影响。在本文中，测试了两种合成高质量二氧化碲起始材料的不同方法，两种方法均使用99.9995%的碲作为前驱体。在第一种情况中，基本上是一种高温氧化过程，将细碲粉进行多阶段的气相或固相氧化过程。在第二种情况中，采用湿法冶金方法，将碲粉溶解在硝酸中，然后以二氧化碲的形式沉淀出来。通过辉光放电质谱法测量纯度，并通过测量与固体样品平衡的气相在442nm处的吸收来确定二氧化碲中的碲含量。这种首次用于测量二氧化碲中游离碲的技术已证明适用于该体系，具有良好的灵敏度和重复性。虽然99.9995%碲粉的高温氧化（气相氧化或固态扩散）能够保持材料的纯度，但当通过湿化学方法合成二氧化碲时，观察到有杂质掺入，导致纯度为99.999%。然而，后一种技术在化学计量比方面的偏差最小。