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Very Small Gallium: Two significant advances in materials during the past year have been (1) the growth of much better gallium arsenide and gallium phosphide single crystals through the use of liquid epitaxy techniques, and (2) the synthesis of new single-crystalline materials such as lithium tantalate and barium sodium niobate. The gallium arsenide and gallium phosphide crystals have been used in constructing improved solid-state lasers, electroluminescent lamps, and Gunn oscillators, while the latter materials have been used in nonlinear optical systems.
When a radioactive substance is more volatile nan any impurity, it can be purified in a carrier-ree condition by distillation. Gallium and iron an be separated either on an anion-exchange olumn or by solvent extraction. In either case areful control of conditions is required to achieve iigh purity. However, the chlorides of gallium nd iron can be sealed in an evacuated tube where he more volatile gallium chloride in carrier-free orm is readily separated from many milligrams if iron by the warming of the mixture with a orch.
Epitaxial growth of single-crystal material, the growth of crystalline material as an extension of the identical crystal structure of another material, can be accomplished starting either with a Vo,iA ot a $3&. VkM ef>a*>j, NcV ^as, OIQ;-nated in 1961, found only limited use until recently, when it was shown that very small gallium pure gallium arsenide crystals containing relatively few defects in structure could be grown by slow-cooling liquid gallium to which an appropriate solute had been added.
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