Thermodynamics of the Mg–B system: Implications for the deposition of MgB2 thin films

We have studied the thermodynamics of the Mg–B system with the calculation of phase diagrams modeling technique using a computerized optimization procedure. Temperature–composition, pressure–composition, and pressure–temperature phase diagrams under different conditions are obtained. The results provide helpful insights into appropriate processing conditions for thin films of the superconducting phase, MgB2, including the identification of the pressure–temperature region for adsorption-controlled growth. Due to the high volatility of Mg, MgB2 is thermodynamically stable only under fairly high-Mg overpressures for likely growth temperatures. This places severe temperature constraints on deposition techniques employing high-vacuum conditions.