Analysis of contact-less crystal growth characteristics of mercurous chloride by numerical simulations and experiments in physical vapor transport

An experimental contact-free crystal growth technique was developed using mercurous chloride. Mercurous halides have low thermal conductivity and very high anisotropy, which causes thermal stress in the crystals during and after growth. Thermal stress enhances cracking and inhomogeneity in the refractive index, which results in high scattering. Firstly, several apparatus for purifying and growing mercurous chloride crystals were designed and constructed to achieve the best result. Secondly, experiments were performed using different types of purification columns to establish the best in order to purify the source materials. Then, several experiments were undertaken to assess the growth of mercurous chloride crystals using different ampoules and different temperature distributions. Finally, heating and cooling procedures had to be developed to avoid cracking the crystal during experiments. One of the issues related to crystal growth is thermal convection. Numerical simulations were used to guide the design of the experiments to minimize these effects. The simulations were achieved using three commercial codes, CFD-2000, Field View and Tecplot. The geometry of the ampoules and their thermal boundary conditions were systematically changed in the simulations to achieve acceptable thermal convection field. Subsequent experiments resulted in homogeneous and extremely transparent mushroom shaped Single crystals.