Choosing a Flux

Although phase diagrams provide valuable information on proper growth conditions, they cannot be used to predict the size and quality of the crystals that will result from flux growth. While these features of crystals depend on the combination of various factors, the limits of what can be achieved in size and quality are often determined by the properties of the flux, and how the flux interacts with the solute compound at high temperatures. This chapter lists the 10 properties of an ideal flux, and discusses why these properties are important for successful flux growth. It is shown that as an ideal flux does not exist in most cases, a compromise is frequently made and a suitable flux is chosen based on the most important requirements. Also, a combination of compounds is often used to optimize properties. This chapter then discusses the typical fluxes used for growth of oxide compounds, using tables to show their basic properties and some of the crystals grown from these fluxes. Similar discussion then follows on growth of intermetallic compounds, where metallic elements are often used as a flux.