Behavior of Disordered Materials under Extreme Conditions

A joint experimental and theoretical study on the behaviors of disorderedchalcogenides (i.e., amorphous As2Se3 and amorphous AsSe) under high-pressure,behaviors of chemically disordered high entropy alloys (HEAs) under high-pressure andhigh-temperature, and low temperature dynamics of Zr-based metallic glasses (MGs) ispresented. A brief introduction, experimental methods and behavior of the studiedmaterials under extreme conditions of temperature and pressure are documented.A reversible breakdown of intermediate range ordering (IRO) and associated networktransition is observed under pressure in amorphous As2Se3. Such a networktransformation is found to be gradual without any sudden jump in density.A reversible pressure-induced crystallization is observed in amorphous As2Se3. Thehigh pressure FCC phase is found to be metastable due to possessing excess amount offree energy, and upon decompression the amorphous phase is found to be retrieved.Surprisingly, the as-prepared amorphous phase and the amorphous phase recovered fromthe complete decompression of the high-pressure crystalline phase are found to beidentical within the theoretical and experimental uncertainty. This is first time that anamorphous material, after going through pressure-induced crystallization, is seen torecover its virgin local structure upon complete decompression, which is the exactnovelty 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 indensity.Behaviors of chemically disordered high entropy alloys (HEAs) under high-pressureand high-temperature have been studied. For the studied HEAs, equations of state aredeveloped under high-pressure, and linear and volumetric thermal expansions aredocumented under high-temperature. The HEAs are found to be stable under both thehigh-pressure and high-temperature, and no phase transition is seen to occur up to thehighest pressure and temperature achieved in the current study.The low temperature dynamics and the possible origin of boson peak in the Zr-basedmetallic glasses have also been described in the current thesis. A universal correlationbetween the local structure and boson peak is established for the Zr-based metallicglasses. The boson peak is found to be originated from the vibrations caused in thedensity fluctuation regions in the metallic glasses