Phase equilibria and thermodynamics of solid state contact reactions in the ternary TaGaAs system

✍ Scribed by Q. Han; R. Schmid-Fetzer

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 729 KB
• Volume: 22
• Category: Article
• ISSN: 0921-5107
• DOI: 10.1016/0921-5107(94)90236-4

✦ Synopsis

The phase equilibria of the ternary Ta-Ga-As system and the binary Ta-Ga and Ta-As systems were determined using X-ray diffraction of samples annealed at 800 °C and differential thermal analysis up to 1400 °C. In the binary Ta-Ga system, peritectic melting of the compounds TaGa3 (520 *C) and TasGa 3 (1060 *C) was detected and a phase diagram is proposed which explains the conflicting literature data for phases in this system. The ternary isothermal section at 800 °C was determined and the two invariant reactions L+ TaAs ~ GaAs + TaGa 3 at 455 *C and L+ Ta5Ga 3 ~TaAs + TaGa 2 at 908 *C were identified. The polythermal liquid + solid equilibria are developed schematically, comprising a total of six invariant reactions plus additional equilibria with the gas phase. Tantalum and the compounds TaGa2, TaaGa2, Ta5Ga 3 and Ta3As are not in equilibrium with GaAs at any temperature. However, TaGaa, TaAs and Tams 2 are stable on GaAs at 1 bar up to 455 *C, 1150 °C and 950 *C respectively. These phases, especially TaAs, may be used to reduce the reactivity at a Ta-GaAs interface. Based on the ternary solid state equilibria the thermodynamic data are deduced and the thermodynamic driving forces of all possible competing reactions at the Ta-GaAs interface are calculated. These data support quantitatively the interpretation of the reactions observed in Ta/GaAs diffusion couples.