Zoltan Kish

I would like to add following information in the conditions stated above by   Zolten Kish

• Whether crystal is attached or detached with container
• Low temperature gradient in crystal growth process
• Elimination of the thermal stress of the container
• Reduced melt convection
• Reduced influence of the gravity

The detached crystal showed the large single crystal with enhanced crystallinity and improved crystal properties. Therefore, crystal growth experiment have performed in microgravity since 1974..

This is so because thermodynamics is more involved for a ternary compound! For example, it can be that there are regimes in which binary sub-compounds might be more stable than the true ternary; this goes under spinodal/binodal decomposition (cf. https://en.wikipedia.org/wiki/Spinodal_decomposition and https://en.wikipedia.org/wiki/Binodal).

Single crystal growth quality and size depend on many conditions, for examples:

• Melting point
• Meting type (congruent or incongruent)
• Phase interactions (phase diagram)
• Temperature difference
• Crystal growth rate
• Vapour pressure of components
• Crystal structure
• Solubility of components in the liquid and solid states
• Etc.

In addition, if we have more components, it is more difficult to archive equilibrium among the components during phase transition of vapour-liquid-solid or vapour-solid without crystal defect introductions. Therefore, based on above conditions in the most cases, it is more difficult to grow of multi-component single crystal than single crystal for single component compound.  One of the reasons to grow singe crystal of LaAlO3 is high meting point - 2080 °C.

Zoltan Kish

I would like to add following information in the conditions stated above by   Zolten Kish

• Whether crystal is attached or detached with container
• Low temperature gradient in crystal growth process
• Elimination of the thermal stress of the container
• Reduced melt convection
• Reduced influence of the gravity

The detached crystal showed the large single crystal with enhanced crystallinity and improved crystal properties. Therefore, crystal growth experiment have performed in microgravity since 1974..

The above answers have already provided a description of many phenomena involved in crystal growth, which influence the difficulty of producing large area single crystals of ternary compounds.

I would like to provide a more intuitive answer. In general, dislocations and stresses are minimized in a single crystal of one element in which all the chemical bonds are covalent bonds. Indeed, covalent bonds provide a very rigid structure with bonds at a very definite angle. The best example is silicon, for which we can achieve very large crystals with few dislocations. Carbon crystals (diamonds) are an exception, indeed it is very difficult to produce large area diamond because of the peculiar growth condition this crystal needs.  When you introduce another element, you introduce ionic chemical bonds (or at least partially ionic) since there is always an electronegativity difference between two elements. Ionic bonds are not so direction-dependent, so you introduce dislocations in your single crystal, and long-range stress that tend to grow with the dimension of your crystal. A good example is GaAs, which now we can produce pretty well (even if not as well as silicon), but at the beginning we could produce just in small pieces. In compounds of three elements, these phenomena become even more intense, leading to more dislocations and a raising difficulty to produce large single crystals.

Hope it helped.