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, ${\mathrm{MgB}}_{\mathrm{2}},$ including the identification of the pressure–temperature region for adsorption-controlled growth. Due to the high volatility of Mg, ${\mathrm{MgB}}_{\mathrm{2}}$ 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.