SOLID-STATE PHASE-EQUILIBRIA IN THE NI-GA-SB SYSTEM - EXPERIMENTAL AND CALCULATED DETERMINATIONS

Solid state phase equilibria in the ternary Ni-Ga-Sb diagram were esta blished at 600-degrees-C. The experimental techniques used to elaborat e the phase equilibria were X-ray diffraction, electron probe microana lysis and scanning electron microscopy. A ternary phase with the nomin al formula Ni3GaSb (designated as A-phase in the present study) was ev idenced. This phase exists over a broad range of homogeneity and exhib its hexagonal symmetry with a disordered structure derivative from NiA s and Ni2In types. Very limited solid solubilities were measured in th e constituent binary Ni-Ga and Ni-Sb compounds, with the exception of NiSb which showed a homogeneity range with a Ga-rich limit correspondi ng to the formula Ni2Ga0.25Sb1.75. The phases GaSb, Ni2Ga3 and substit uted-NiSb coexist with each other to form a three-phase equilibrium th at dominates the GaSb side of the phase diagram. This part of the expe rimental diagram is in agreement with the calculated one from availabl e experimental thermodynamic data on the Ga-Sb, Ni-Ga and Ni-Sb binari es and with interfacial reaction studies which concluded that Ni2Ga3 a nd substituted-NiSb are the stable phases when Ni thin films are react ed to completion on GaSb. A comparative study with the Ni-Ga-As and Ni -Al-As phase diagrams is also given which points out that, contrary to NiGa (NiAl) with GaAs (AlAs), the monogallide NiGa is not in thermody namic equilibrium with GaSb.