The Origin of the Anomalous Expansion of the First Peak in the Radial Distribution Function During the Rapid Solidification of Tantalum Metal

Abstract

The cause of the anomalous shift in the first maximum peak of radial distribution functions (RDFs) with decreasing temperature in metallic melts and glasses remains highly controversial. In this study, we show that the first RDF peak exhibits anomalous expansion as the temperature decreases during the non-equilibrium solidification (r1=1×1010 K/s and r2=1×1011 K/s) of liquid tantalum. This behavior is primarily due to alterations in both the geometric and electronic structures of the system. In terms of geometric structure, for example, at the cooling rate of r1, the system forms a significant number of cage-like icositetrahedral Voronoi polyhedra (0,0,12,2) and standard icosahedral Voronoi polyhedra (0,0,12,0) at low temperatures. These Voronoi polyhedra have longer bond lengths and lower binding energies compared to their high-temperature counterparts. Furthermore, these Voronoi polyhedra nest together, forming a stable Ta26-C2v atomic configuration with minimal changes in bond lengths. This unique geometric arrangement contributes fundamentally to the anomalous expansion of the first peak of the RDF. Regarding the electronic structure, temperature influences the interactions between Ta atoms. At higher temperatures, the electronic localization functions (ELF) and the Mulliken bond overlap populations (Qi–j) are significantly increased, leading to stronger electronic interactions and a denser arrangement of nearest-neighbor atoms with shorter bond lengths. Consequently, the combined effects of geometric and electronic structural changes during non-equilibrium solidification could explain the anomalous expansion of the first peak of the RDF.