Invariance of liquid bismuth structure along the melting curve

Bismuth exhibits remarkable structural and thermodynamic behavior under pressure, as indicated by an anomalous melting curve, transitions between multiple low-symmetry solid allotropes, and multiple reports of liquid transitions. Despite extensive studies at ambient pressure, the structure of liquid Bi at high pressures remains poorly understood. Using synchrotron radiation energy-dispersive X-ray diffraction measurements, we investigate the liquid Bi structure just above the melting line over 1.0−4.0 GPa. Remarkably, the liquid structure remains unvarying as the underlying solid phases change dramatically. The first peak in the g(r) shifts ~ 0.004 nm to higher r values (~ 1%), despite increasing density, while the second peak moves ~ 0.01 nm to lower r values (~ 1.5%). Coordination numbers of the first and second shells increase with density. Structural analysis using the Quasi-Crystalline Model reveals a persistent Bi−I rhombohedral-like short-range order. These findings highlight unexpected structural stability in liquid bismuth under pressure, challenging conventional views on pressure-induced liquid transitions.