以溶膠-凝膠法製備之ABO3-型鈣鈦礦結構的晶格動力學研究

Abstract

本研究之主要目的是探討在ABO3-型鈣鈦礦材料中，不同A原子的取代對於材料結構上的影響。經由晶格動力學的分析，我們可以確定在鐵電狀態下Ba-O是離子鍵結，而Pb-O則是以共價鍵結的型式存在。鍵結型式的差異直接造成不同的縱光-橫光聲子分裂現象。此外藉由觀察以鈦酸鉛為基底的鈣鈦礦材料中A1(1TO)的非簡諧行為，可以了解鈣、鍶和鋇等不同原子的攙雜對於非簡諧行為的影響。在攙鉺的鈦酸鍶鋇(Ba0.7Sr0.3TiO3)薄膜的結構分析、光學特性與介電係數量測中，我們也發現了此薄膜不僅保有鈦酸鍶鋇薄膜良好的電性，其螢光頻譜更顯示出在鉺濃度為3mol%與退火溫度為700OC的條件下，此攙鉺薄膜具有最佳的螢光強度(波長約550 nm)。

This dissertation investigates the lattice dynamics of ABO3-type perovskite polycrystalline by Raman spectroscopy, and the luminescence mechanism of erbium-doped Ba0.7Sr0.3TiO3 thin films, where all samples were prepared by the sol-gel technique. In the case of BaxSr1-xTiO3 (BST) system, we have found the giant splitting of longitudinal optical (LO) and transverse optical (TO) phonon modes while x lower from 1 toward 0.7. However, decreasing LO-TO splitting, which is totally different from in the BST system, was observed in PbxSr1-xTiO3 (PST) system. This is the first direct observation of the influence on lattice dynamics due to diverse chemical bonding. Pb-O interaction is proposed to be more hybridized than Ba-O, and thus the change of effective charge to the LO-TO splitting may be the dominant mechanism in PST, while unit-cell volume change is in the BST systems. We have also studied the diversity of the anharmonic effects of the lowest-frequency A1(TO) mode in PbxCa1-xTiO3 (PCT), PbxBa1-xTiO3 and PbxSr1-xTiO3 systems for x changing from 0.6 to 1.0. Based on the anharmonic approximation in the interatomic potential, we qualitatively illustrate the energy transfer between the subpeaks of the A1(1TO) mode of PCT. Comparison of the line shapes of A1(1TO) mode among three PbTiO3-based perovskites indicate that the anharmonicity will become more conspicuous due to the larger high-order potential terms of Ba2+ and Ca2+ substitution than Sr2+ substitution for Pb2+. Furthermore, the dependence of luminescence efficiency on Er3+ concentration and sintering temperature in the Er-doped Ba0.7Sr0.3TiO3 thin films is governed by crystallinity and ion-ion interaction. Our investigations indicate that the observed green emission reaches maximum at sintering temperature 700OC and 3 mol% Er3+ concentration. All experimental data will provide useful information to support further theoretical calculations on lattice dynamics and development in photonic devices of ABO3 perovskites.