TeO_2 liquid phase: Viscosity measurements and evaluation of the thermal conductivity from crystal growth experiments

摘要

Current applications of paratellurite TeO_2 in optics and nuclear physics require improving the yield and optical quality of synthesized single crystals. Modelling of the growth process is a useful tool for such purpose, however, involving the knowledge of several thermodynamic parameters of both solid and liquid phase of the compound. This work describes the determination of two main unknown ones, namely dynamic viscosity η and thermal conductivity λ_1 of the liquid phase. Measurements of η are performed by means of a specifically designed apparatus; over a 40 K temperature interval above the melting point we find a mean value of 0.028 Pa.s. This data is used in commercial software to depict the evolution of the solid-liquid interface in our Bridgman growth setup. Comparison of the distribution of defects observed in grown ingots with the results of modelling allows estimating λ_1 as lying in the range 3.50-3.75 W m~(-1) K~(-1).