Association Between High-pressure Phase Transition And Electronic Structure Of Atoms In Rare-earth-based Amorphous Alloy

Since their discovery, metallic glasses (MGs) have become popular research topicsbecause of their excellent mechanical, magnetic, physical and chemical properties.However, the structures of MGs as well as the relations between their structures andproperties remain poorly understood. The discovery of polyamorphic transitions in rareearth-based MGs provides a new approach for investigating the structures and propertiesof MGs. However, the correlations between polyamorphic transitions in MGs and theatomic and electronic structures of glass components have not been clearly described. Inthis thesis, correlations between the atomic and electronic structures of glass componentsand polyamorphic transitions in rare earth-based MGs under high pressure were assessedusing in-situ high pressure synchrotron X-ray technology.The structures of Pr60Cu20Al10Ni10and Yb60Ca2.5Zn20Mg17.5MGs were investigatedusing in-situ high pressure synchrotron X-ray. Polyamorphic transition, which refers tothe transformation of low density amorphous (LDA) to high density amorphous (HDA)was previously discovered in two MGs with a collapsed volume and mutatedcompression ratio. Without4f electronic structure, in-situ high pressure synchrotronX-ray of Zr59.63Cu15.75Al14.62Ni10MG confirmed that pressure-induced polyamorphismin Pr-and Yb-based MGs are closely related to4f electrons.The structures of Ce68Al10Cu20Co2, Ce34La34Al10Cu20Co2, and La68Al10Cu20Co2MGs were also investigated by applying in-situ high-pressure synchrotron X-ray.Polyamorphic transitions occured in Ce68Al10Cu20Co2and Ce34La34Al10Cu20Co2MGs.The transition pressure and volume collapse were altered after addition of La. Comparedwith the structure evolution of La68Al10Cu20Co2MG sample, polyamorphic transitions inrare earth-based MGs are correlated with4f electrons.By applying in-situ high-pressure synchrotron X-ray technologies to studyMg65Cu25Tb10as a model system, no mulations in volume reduction, structure factor plot,and pair distribution function peaks were observed, these findings indicate thatpolyamorphic transition dose not occur in Mg-based MGs. Further analysis shown thatdelocalization of4f electrons occur only in solvent atoms and not in solute atoms surrounded by solvent atoms. Therefore, the change of the solvent metallic4f electronicstate is essentially responsible for the polyamorphic transitions in MG.Structural relaxtion of Fe80P11C9and Ce65.5Al10Cu22.5Co2MG under high pressurewas explored using in-situ high-pressure synchrotron X-ray. The structural evolution ofMGs under a pressurized and repeated pressure was analyzed. Analysis of structurefactors and pair distribution functions indicated that polyamorphic transitions dose notoccur in Fe80P11C9MG, and the average and nearest-interatomic distances decrease withannihilation of free volumes, thereby forming a highly dense randomly packed structure.Hysteresis of the volume change was observed during decompression. A throughinvestigation of Ce65.5Al10Cu22.5Co2MG revealed that polyamorphic transition ccursduring compression and decompression. These results indicate that the polyamorphictransition is reversible. Hysteresis occurred when the polyamorphic transitions transformfrom HDA to LDA.The effets of high pressure on the structure relaxation and crystalline kinetics ofPr55Cu17Ni8Al20and La68Al10Cu20Co2MGs were investigated. The study indicated thatthe pressure could promote the structure relaxation process of MGs, leads to theannihilation of free volume, improve the crystallization activation energy and hardness ofmetallic glass.