High-pressure phase diagram of Bi-Ga: Polymorphism, anomalous melting curves and liquid miscibility gap

The high-pressure states of the elements can significantly impact the phase diagrams of their alloys due to polymorphism in the solid state and anomalies and slope changes in the melting curve. Here, we investigate the effect of these characteristics on a model system, the Bi-Ga system, by constructing a thermodynamic model of the high-pressure phase diagram and validating the proposed transitions by electrical resistance measurements in a ‘Paris-Edinburgh’ press. We achieve conclusive agreement between our calculated phase diagram up to 6 GPa and the measured transitions. At higher pressures, the liquid miscibility gap in this system disappears, and the phase diagram changes from a monotectic to a eutectic type at a pressure of 8 GPa. We also measured the monotectic temperature and the liquidus of Bi-rich alloy that presents anomalous behavior as a function of pressure. The present contribution demonstrates the crucial contribution of the high-pressure behavior of the elements in characterizing the challenging and complex behavior of alloys under pressure.