The Structure-Thermodynamic State and the Mechanism of Crystallization of Gallium-Based Melts

Quantitative analysis of the structure factors and curves of radial distribution of atoms obtained as a result of X-ray study in a wide temperature range reveals a fundamental difference in the structure of melts of normal close-packed metals and semimetals $(\text{Ga}$, $\text{Bi})$. The results of calculation of the temperature dependence of the configurational component of entropy of semimetals confirm the presence of a covalent component of cluster type in the microheterogeneous structure of melts. The melting-crystallization processes, studied using the method of acoustic emission, exhibit a stepwise pattern for semimetals which is due to the incoherence of the metal and covalent components of the structure. The process of crystallization of gallium- and bismuth-based eutectic alloys is complicated by the presence of quasi-eutectic microsegregation, which affects both the structure parameters and configurational component of entropy.