Cluster compounds formation in metal alloys crystals

Abstract

The formation and physical origin of the pre-cluster complexes and pre-phase (cluster) compounds have been studied on cast magnesium alloys (in the liquid and solid states) as well as other primary solutions enriched with excess (non-intrinsic, structural) vacancies. The results produced by DSC, TEM observation, Auger-electron, UV-and X-ray photoelectron spectroscopy techniques were combined with positron annihilation, electroresistance, and internal friction measurements to evaluate different stages of the cluster compounds formation and to examine the strength of their chemical bonding in terms of a detailed analysis of electron-sensitive properties. The thermally activated deviations from classical (Arrhenius) behaviour in hydrogen-charged hcp and fcc metal crystals are found to be caused by the nucleation of the solute/excess vacancy complexes. Additional support for this short-range self-supported mechanism comes from data obtained by mechanical spectroscopy and positron annihilation. These pre-cluster separations are assumed to act as nuclei for the synthesis of the cluster compounds such as Mg16Ba2 and Al18Ba9 with own electronic (hybridized) structure in hcp magnesium- and fcc aluminium alloy crystals, respectively. A unified concept of the liquid/solid conversion for condensed cluster-forming alloys is considered. This approach is particularly useful for the development of chemically combined cluster compounds with own electronic configurations as functional materials for high-current electronics.