以鈦酸鉛為基底之鈣鈦礦晶格動力學研究

Abstract

以鈦酸鉛為基底之鈣鈦礦晶格動力學研究 研究生：李春霆 指導教授：謝文峰 教授 張振雄 教授 國立交通大學光電工程研究所 摘要 為了比對過去的多晶結構BaxSr1-xTiO3 [Phys. Rev. B. 64, 224103-1 (2001)] 有著明顯增加的LO-TO splitting現象，我們從摻雜不同的成分中發現在PbxSr1-xTiO3和 PbxCa1-xTiO3 系統中最低頻的A1 (1TO)模與最高頻的A1(3LO)模的LO-TO splitting現象卻有著逐漸減少的趨勢。 對於晶格動力學而言，相似的結構但是確有著不一樣的splitting現象的原因是由於Pb2+ 與Ba2+的電子狀態不同而導致，我們提出此原因是由於Pb-O的共價鍵影響大於Ba-O的離子鍵而導致庫倫力的影響被減弱。除此之外，我們從拉曼的光譜圖中發現，由tetragonal變成cubic的過程，PbxCa1-xTiO3 系統中最低頻的A1 (1TO)模有著非簡諧的效應影響。我們從適用的位能圖中，定性的分析出A1 (1TO)模中的 subpeaks對應於相鄰間的能階躍遷，且與純的PbTiO3來比較，發覺在相變的過程中也有著相同的趨勢。

Study on lattice dynamics of PbTiO3-based perovskites Student: Chung-Ting Li Advisor: Prof. Wen-Feng Hsieh Prof. Chen-Hsiung Chang Institute of Electro-optical Engineering National Chaio Tung University Abstract Contrast to the increase of giant LO-TO splitting in polycrystalline BaxSr1-xTiO3 [Phys. Rev. B. 64, 224103-1 (2001)], a direct observation of the decrease splitting of the softest A1 (1TO) and the hardest A1(3LO) modes were reported in PbxSr1-xTiO3 and PbxCa1-xTiO3 systems. Similar structure but anomalous discrepancies on lattice dynamics is related to the diverse electronic states of Pb2+ and Ba2+ ions. It is proposed that the Pb-O interaction is more hybridized than Ba-O, therefore, reduces the effect of long-range Coulomb interaction. While tetragonal phase toward cubic phase, we find that the diversity of the anharmonicity of the lowest-frequency A1(1TO) mode of the PbxCa1-xTiO3 system was performed using Raman spectroscopy from tetragonal toward cubic phase. From the analyses of Raman spectra, we qualitatively illustrate the energy transfer between the subpeaks of the A1(1TO) mode based on the anharmonic in the interatomic potential. Comparison of the line shapes of A1(1TO) mode with pure PbTiO3 perovskites indicate that the anharmonicity will become conspicuous.