Abstract
Phase relations in the system Ni-Sb-Te were studied in evacuated silica glass tubes to construct the 400 degrees C isothermal section. Two extensive ternary solid-solutions were detected in the system, lambda(1), Ni(Sb(1-x)Te(x))(1+y) (0 { x { 1, where, for x }= 0.9, the relation 0.09 {= y {= 1 applies), and lambda(2), NiSb(1-x)Te(2x) (0.28 { x { 0.66).
Their stability fields are elongate along the NiTe(1.09)-NiSb and NiSb-NiTe(2) joins, respectively, indicating extensive Sb-for-Te substitution. These two solid solutions are breakdown products of the broad NiSb-NiTe-NiTe(2) solid solution that dominates the system at temperatures higher than 690 degrees C.
The mineral vavrinite, Ni(2)SbTe(2), is a part of the lambda(2) solid solution at 400 degrees C. The average crystal structure of the lambda(2) solid solution is of the CdI(2)- or NiAs-type at 400 degrees C; Sb and Te atoms occupy the same crystallographic position (i.e., Sb, Te mixed site).
The lambda(1) solid solution displays the NiAs-type structure along the NiTe(1.09)-NiSb join; toward NiTe(2) composition, the phase was found to be of the CdI(2) type. Nisbite, NiSb(2), dissolves 8.4 at.% Te at 400 degrees C.
Phases Ni(7)Sb(3), beta(2) (Ni(3-delta)Te(2)), gamma(1) (NiTe(0.775)) and A (Ni(5.66)SbTe(2)), hitherto unknown as minerals, can be expected in mafic and ultramafic rocks, in close association with melonite and breithauptite.