Browsing by Subject "Ga2O3"
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(2022)Amorphous metal oxides have proven to deform in a plastic manner at microscopic scale. In this study the plastic deformation and elastic properties of amorphous metal oxides are studied at microscopic scale using classical molecular dynamics simulations. Amorphous solids differ from crystalline solids by not having a regular lattice nor long range order. In this study the amorphous materials were created in simulations by melt-quenching. The glass transition temperature (Tg) depends on the material and cooling rate. The effect of cooling rate was studied with aluminiumoxide (Al2O3) by creating a simulation cell of 115 200 atoms and melt-quenching it with cooling rates of 1011 , 1012 and 1013 K/s. It was observed that faster cooling rates yield higher Tg. The Al2O3 was cooled to 300 K and 50 K after which the material was stretched. The stress-strain curve of the material showed that samples with higher Tg deforms in plastic manner with smaller stresses. The system stretched at 50 K had higher ultimate tensile strength than the system stretched at 300 K and thus confirming the hypothesis proposed by Frankberg about activating plastic flow with work. In order to see if the plastic phenomena can be generalized to other amorphous metal oxides the tensile simulation was performed also with a-Ga2O3 by creating a simulation cell of 105 000 atoms, melt-quenching it and then stretching. Due to the lack of parameters for Buckingham potential these parameters were fitted with GULP using the elastic properties and crystalline structure of Ga2O3. The elastic properties of Ga2O3 with the fitted potential parameters agreed very well with the literature values. The elongated a-Ga2O3 behaved in a very similar fashion compared to a-Al2O3 cooled with the same cooling rate. Further work is needed to establish the Buckingham potential parameters of a-Ga2O3 by experimen tal work. The potential can also be developed further by using the elastic constants and structures of amorphous a-Ga2O3 in the fitting process, although the potential shows already very promising results.
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(2023)Ga2O3 has been found to exhibit excellent radiation hardness properties, making it an ideal candidate for use in a variety of applications that involve exposure to ionizing radiation, such as in space exploration, nuclear power generation, and medical imaging. Understanding the behaviour of Ga2O3 under irradiation is therefore crucial for optimizing its performance in these applications and ensuring their safe and efficient operation. There are five commonly identified polymorphs of Ga2O3 , namely, β, α, γ, δ and structures, among these phases, β-Ga2O3 is the most stable crystal structure and has attracted majority of the recent attention. In this thesis, we used molecular dynamic simulations with the newly developed machine learned Gaussian approximation potentials to investigate the radiation damage in β-Ga2O3 . We inspected the gradual structural change in β-Ga2O3 lattice with increase doses of Frenkel pairs implantations. The results revealed that O-Frenkel pairs have a strong tendency to recombine and return to their original sublattice sites. When Ga- and O-Frenkel pairs are implanted to the same cell, the crystal structure was damaged and converted to an amorphous phase at low doses. However, the accumulation of pure Ga-Frenkel pairs in the simulation cells might induce a transition of β to γ-Ga, while O sublattice remains FCC crystal structure, which theoretically demonstrated the recent experiments finding that β- Ga2O3 transfers to the γ phase following ion implantation. To gain a better understanding of the natural behaviour of β-Ga2O3 under irradiation, we utilized collision cascade simulations. The results revealed that O sublattice in the β-Ga2O3 lattice is robust and less susceptible to damage, despite O atoms having higher mobility. The collision and recrystallization process resulted in a greater accumulation of Ga defects than O defects, regardless of PKA atom type. These further revealed that displaced Ga ion hard to recombine to β- Ga lattice, while the FCC stacking of the O sublattice has very strong tendency to recovery. Our theoretical models on the radiation damage of β-Ga2O3 provide insight into the mechanisms underlying defect generation and recovery during experiment ion implantation, which has significant implications for improving Ga2O3 radiation tolerance, as well as optimizing its electronic and optical properties.
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