STRUCTURAL INVESTIGATIONS IN THERMOELECTRIC MATERIALS.
Quarterly rept. no. 4, 1 Jul-30 Sep 63,
MERCK AND CO INC RAHWAY N J
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A study was made of the sulvanite group of compounds. It has been shown that uncontrolled freezing of compositional melts Cu3V, NB, Ta Se, Te4 seldom yields a pure phase. The case of Cu3VTe4 has been dealt with in detail as it is typical, and the rather low melting point makes it convenient to handle. None of the sulvanites thus far examined melts congruently Cu3VTe4 displays a stable and unstable freezing behavior which it follows unpredictably from the unseeded liquid. The unstable branch leads to a solid containing considerable amounts of copper tellurides, notably Rickardite Cu4Te3. Such solid reverts to pure Cu3VTe4 upon annealing. The solid cannot be zone refined if the unstable freezing course occurs, as the capsule invariably shatters. The presence of pure seed phase allows successful zoning to be done. Contrary to the preliminary estimate of the third period, Cu3VTe4 is a non-degenerate semiconductor degeneracy is a characteristic of Rickardite contamination. Possible compounds isoelectronic and isostructural with the sulvanites such as IIb3VIbVa4 and IIb3VIIbIVa4 are being sought. To date, none has been found.