Extra pure tellurium oxide for the growth of high quality paratellurite crystals

Abstract

Tellurium oxide (IV) single crystals are in demand materials for manufacturing acousto-optical devices optical fibers for IR wavelength range. The initial material for production of active and passive optical materials must have purity better than 99.999 wt% and extremely low concentration of the residual water. The main method of synthesis of TeO2 is oxidation in nitric acid followed by recrystallization from HCl is complicated, also amount of used high purity acids and waste are very high. Besides the residual water content is no less than 10 ppm. In the research we have developed the procedure for the synthesis of high-purity tellurium (IV) oxide without the usage of liquid oxidants. The process of oxidation of elementary Te was carried out in a flowing quartz glass reactor. Air oxygen was used as an oxidizing agent. The oxidation was conducted at 600-670°C during 24 hours. The produced material was a fine crystalline powder of acicular dendritic crystals of bright white color, identified as β-TeO2 due to X-ray. It was as pure as 5N7 due to ICP-MS. The β-TeO2 crystal grown form the synthesized water-free preparation has demonstrated better optical properties towards the crystals grown from commercial TeO2, produced by the «wet» technology.