Flow fields and interface shapes during horizontal Bridgman growth of fluorides

Abstract

A two-dimensional analysis of horizontal Bridgman crystal growth is presented. Material properties are close to those of lithium calcium aluminium fluoride (LICAF), while operating parameters resemble, on average, those used during growth of fluorides via vertical techniques. Estimates of characteristic timescales, as well as a representative fully transient analysis, demonstrate the quasi-steady nature of heat transport and fluid flow in this system. Results obtained using a quasi-steady-state analysis show that both surface-tension-driven (Marangoni) and buoyancy-driven flow mechanisms have an important influence on the system's thermal field and melt/crystal interface shape. An interface whose curvature is significantly promoted by both flow mechanisms can be rendered relatively flat by modifying the furnace profile. In the uncommon case (existing in some materials, though not LICAF) where melt surface tension increases with increasing temperature Marangoni and buoyancy-driven flows may oppose each other, thus reducing melt/crystal interface deflection.