UC Riverside

Amorphous materials have a wide variety of applications and their mechanical, optical, electronic and magnetic properties hold great promise towards current technologies. Just like in crystalline materials, the bulk properties of amorphous materials are often dictated by defects and other structural anomalies or outliers. However, unlike crystalline structures, amorphous materials lack long range order and the disordered nature of their atomic arrangements poses major challenges toward building a quantitative correlation between their local atomic environments, leading to complications in characterizing the structure and relaxation in these materials. This dissertation is composed of three separate studies that together build a methodology for describing and understanding the role of defects in amorphous materials. In one of the projects, the structures of the defects are all well-defined but their mechanical response is unknown and is the focus of our study. On the other hand, the other two studies involve understanding the structure of non-crystalline materials. In one of the studies, the challenge is in characterizing the average structure, its relationship to viscosity, characterizing thermodynamically-driven changes in structures, and quantifying the degree of amorphousness. In a final study, we identify the outliers in amorphous materials, we use metrics of structure and then we find the corresponding mechanical behaviour and response of these outliers. These three combined can establish relationship between defects, defects’ structure and their properties in materials. In this thesis, firstly, we investigate the phenomenon of fragility in amorphous liquids, which characterizes the dynamics of amorphous glass-liquid and refers to the sensitivity of liquid’s bonding network and is associated with non-Arrhenius dependence of the liquid’s viscosity. We demonstrate how fragility in amorphous liquids correlates with atomic size-mismatch which is an important consideration in the design and structural performance of glass forming alloys. Secondly, new computational methods are put forward to explain the numerical values of some useful amorphous configurations to achieve a greater understanding of the relationship between their processing, structure, and properties. Understanding the structure and the weaknesses of amorphous materials is of great importance to determine their physical and mechanical properties and to improve the materials’ design. For this purpose, predictive models were developed to accurately classify and identify the defects in amorphous materials and characterize their structural features. We also illustrate the effect of different cooling rates on these local weaknesses. Lastly, we studied the evolution of the thermal conductivity in pristine LiAlO2 and we elucidated the effects of defects on its thermal properties at different scales which is important to assure its long-term performance and to address these defects appropriately. These contributions are anticipated to enhance our understanding of structure-property relationships of defects in materials, leading to establish useful approaches in searching for materials with desirable performance.