Behavior Of Disordered Materials Under Extreme Conditions

A joint experimental and theoretical study on the behaviors of disordered chalcogenides ?i.e., amorphous As₂Se₃ and amorphous AsSe? under high-pressure, behaviors of chemically disordered high entropy alloys ?HEAs? under high-pressure and high-temperature, and low temperature dynamics of Zr-based metallic glasses ?MGs? is presented. A brief introduction, experimental methods and behavior of the studied materials under extreme conditions of temperature and pressure are documented. A reversible breakdown of intermediate range ordering ?IRO? and associated network transition is observed under pressure in amorphous As₂Se₃. Such a network transformation is found to be gradual without any sudden jump in density.A reversible pressure-induced crystallization is observed in amorphous As₂Se₃. The high pressure FCC phase is found to be metastable due to possessing excess amount of free energy, and upon decompression the amorphous phase is found to be retrieved. Surprisingly, the as-prepared amorphous phase and the amorphous phase recovered from the complete decompression of the high-pressure crystalline phase are found to be identical within the theoretical and experimental uncertainty. This is first time that an amorphous material, after going through pressure-induced crystallization, is seen to recover its virgin local structure upon complete decompression, which is the exact novelty in the current thesis.Similar to amorphous As₂Se₃, a reversible breakdown of intermediate range ordering ?IRO? and associated network transition is observed under pressure in amorphous AsSe. Such a network transformation is found to be gradual without any sudden jump in density.Behaviors of chemically disordered high entropy alloys ?HEAs? under high-pressure and high-temperature have been studied. For the studied HEAs, equations of state are developed under high-pressure, and linear and volumetric thermal expansions are documented under high-temperature. The HEAs are found to be stable under both the high-pressure and high-temperature, and no phase transition is seen to occur up to the highest pressure and temperature achieved in the current study.The low temperature dynamics and the possible origin of boson peak in the Zr-based metallic glasses have also been described in the current thesis. A universal correlation between the local structure and boson peak is established for the Zr-based metallic glasses. The boson peak is found to be originated from the vibrations caused in the density fluctuation regions in the metallic glasses.