高介電氧化物LaAlO3為一個鈣鈦礦結構材料，在高壓下會從菱面體結構相變成立方晶體結構，這個相變過程為一個連續相變。為了了解相變的過程，在本篇論文中，我們透過第一原理密度泛函微擾理論計算，除了觀察在不同壓力下的能量變化外，同時分析其相符的晶體動力學特性。透過Landau theory，可以得到LaAlO3的聲子頻率在不同結構對稱性時，顯示出特有的壓力下聲子軟化現象。並且不同壓力時的拉曼強度與deformation potential也將在本篇中討論。 As a high-k oxide in a perovskite structure, LaAlO3 undergoes a rhombohedral-to-cubic structural phase transition under high pressure. Such phase transition is characterized as a continuous phase transition. In order to study the pressure effect, we use the first principle density functional perturbation theory to calculate the total energies with respect to various pressures in this thesis, and also analyze the corresponding lattice dynamics properties. Based on the Landau theory, calculated phonon frequency of LaAlO3 in different structural symmetries indicates a typical pressure-induced mode softening effect. Moreover, the pressure effects on Raman intensity and the deformation potential is also discussed in this work.
