Understanding the physics of the disordered state: universality of phenomena in glasses and resistance to amorphization by radiation damage

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Amorphous solids are widely used in technological applications. Glasses are very familiar objects to us in our everyday life. However, compared with topologically ordered solids, they are much less understood both experimentally and theoretically. In the last several decades, experimental studies have produced much new data, but the theoretical understanding of this data is still lacking. This proposal will advance fundamental understanding of the physics of the amorphous state, by linking the observed behaviour to microscopic processes in them. The proposal consists of two parts, the microscopic description of universal relaxation phenomena and understanding resistance to amorphization by radiation damage.Over the last three decades, amorphous solids have been fascinating scientists by the universality of their relaxation properties, many of which are not seen in crystals. The first part of this proposal is aimed at obtaining fundamental understanding of the origin of universality of phenomena in amorphous solids, which has long puzzled scientists. I formulate a general question of how the complexity related to the nature of disordered state gives rise to the simplicity (universality) of the observed phenomena. There are several main universality classes in amorphous solids. In the proposed research, the following will be addressed: (a) stretched-exponential relaxation in glasses and supecooled liquids at glass transition; (b) universality of relaxation around the rigidity percolation point; and (c) low-temperature universality of heat capacity and sound absorbtion. I will provide the microscopic description of these phenomena. The important point here is to relate these seemingly different relaxation phenomena, by describing them in terms of the dynamics of universal local relaxation events. These events are the elementary relaxation quanta in glasses which drive the universal relaxationphenomena at the microscopic scale.Particle irradiation is one of the ways of producing amorphous solids, and the second part of this proposal is aimed at understanding what makes a material amorphizable by radiation damage. My interest in this area is stimulated by the need to safely encapsulate highly radioactive nuclear waste and surplus Pu. Why some materials are readily amorphized by heavy energetic ions, whereas others are extremely resistant and do not show any loss of crystallinity even at very high radiation doses? Despite decades of research, the problem of resistance to amorphization by radiation damage is not generally solved. I will investigate the common origin of resistance to amorphization by radiation damage in many materials, using my recent proposal that the type of interatomic interactions, covalency and ionicity, plays an important role in this process. In addition, I will investigate how other factors may be relevant for resistance to amorphization. Finally, I will seek to provide a quantitative microscopic theory that links the microscopic parameters of a material to its resistance to amorphization. This will allow to predict materials with high resistance to amorphization.