The growth of single crystals

A small-scale, controlled atmosphere, gradient furnace is a valuable addition to the laboratory since it allows optimum sintering conditions to be quickly determined. 

Whilst every material presents its own problems in crystal growth, which must be solved experimentally, there is a general thermodynamic principle that gives an indication of how difficult the process is likely to be. Since crystal growth takes place reversibly, the Gibbs energy G must be constant and so, under isothermal conditions, 

If we take AH = La, where La is the latent heat per atom, Jackson s dimensionless parameter a is defined by 

Substance Change of state Temperature 7 cr/A of change of state Latent heat Lju/kJ mol 1 at Tcr a = Lm/AoTcR 

The following methods have been used to grow crystals of oxides. 

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The process of sintering by vapour phase transport is probably important to the growth of single crystals of solids from polycrystalline samples in a closed system, where the vapour species are the transporting gas, which may have the same or different chemical composition from die solid. An example where... 

A halide flux enhances the growth of single crystals of intermetallic compounds such as CaNi, and compounds in the Dy-Mg and Ce-Mg " systems which have... 

In these cases, one is limited to the growth of single crystals of the transition metals since it is those metals which form volatile carbonyl compounds. The alkali metals, alkaline earth metals and certain of those elements which are allotropic in nature are not at aH suited for this type of crystal growth. 

Metal powders can readily react with alkali metal polychalcogenide melts at typical temperatures in the range 200 600°C to afford chalcogen-rich complexes. As discussed in an excellent review article,10 the highly ionic nature of the melt greatly enhances the solubility of the chosen metal and often facilitates the growth of single crystals. 

In a paper by Fisk and Remeika (1989) several points concerning the growth of single crystals from metal fluxes have been discussed. Attention has been dedicated to various aspects of the problem of separating crystal and flux, for which two main approaches, chemical and mechanical, may be considered. The following examples drawn from the preparative chemistry of the rare earth alloys were described. 

Laudice, R. A. The growth of single crystals (Prentice-Hall, Englewood Cliffs, N.J., 1970). 

Unfortunately, a transition from the a phase of Np metal to the P phase occurs at the low temperature of 301 K, making the growth of single crystals of a-Np metal extremely difficult. 

In this chapter, preparation and purification methods are reviewed. In view of the expected role of 5 f electrons in the metallic bond of actinides, methods for the preparation of metals have been particularly studied. There has also been important progress in the preparation of simple binary compounds. Special emphasis has been given to the growth of single crystals, particularly needed for the most refined physical techniques. 

Compounds can be prepared either in polycrystalline form, often referred to as ceramics, or as single crystals. The synthesis of oxides in polycrystalline form is typically straightforward relative to single crystal growth. For the growth of single crystals of complex oxides, a unique growth system appropriate to the chemistry and... 

R. A. Laudise, "The Growth of Single Crystals , Prentice-Hall, NJ, 1970. 

The crystallographic examination required the growth of single crystals, which took time, and was finally accomplished by one of DuPont s foremost crystallographers, Dr. Gunther Teufer. He identified the bonding between rings as 1,2. ... 

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