High temperature solution (flux) and high pressure solution (hydrothermal) crystal growth

Abstract

This review traces the recent developments of high temperature solution (flux) and high pressure solution (hydrothermal) crystal growth. High temperature solution (HTS) growth of oxide materials from ionic liquids (PbO, PbF 2, Bi 2O 3, KF and their combinations) and network-forming liquids (various borates for example) has advanced to the stage of a routine experimental tool. Recent significant improvements in technique include the use of controlled oxygen partial pressures to grow nonstoichiometric oxides and lower valence state oxides directly in equilibrium with a gas atmosphere, the use of moving flux zones modes to grow solid solutions, and the use of isothermal flux-evaporation also to grow solid solutions. Current experimentation is directed toward improved understanding of the physical chemistry of the flux liquids (liquid structure and its influence on growth, location of crystallizing ions in the liquid structure, thermodynamic models for solutions behavior, etc.) and toward the development of novel flux systems for non-oxide materials. High pressure solution (HPS) growth is less advanced as a routine technique because of difficulties with seed crystal surfaces and orientations, selection of workable solvents, and suppression of spontaneous nucleation and crystal flawing. Where these have been solved, however, much better material is grown by HPS methods than HTS methods in general. Research here is directed toward the discovery of useful non-aqueous solvents and a better understanding of the nature of the supercritical fluid and the growth process. HPS methods have very recently been used for growth of large single crystals of metastable phases by use of epitaxy on appropriate substrates.