鈦酸鍶鋇粉末的結構相變與單晶薄膜成長之研究

Abstract

本文主旨在研究鈦酸鍶鋇(BST)在發生結構相變時的光學特性，利用sol-gel方法製備一系列不同成分比例的鈦酸鍶鋇粉末材料，經由x-ray繞射數據計算其晶格常數，發現在室溫時x接近0.7會發生結構的相變，且晶格常數的變化不滿足線性的Vegard law。在x 0.4附近也有不連續的轉折。從拉曼散射光譜量測上，發現在立方體結構(x<0.7)的BST會因一些不規則的晶格排列造成拉曼散射，因此在拉曼光譜上仍有訊號可見。隨著BST發生結構相變(x=0.7)時，在305cm-1、186cm-1和720cm-1的峰值都會逐漸消失。利用三個A1模相互耦合的模型，對我們拉曼光譜訊號做擬合，並發現在186cm-1處的A1模確實是因三個A1模彼此之間不協調耦合才會形成一個凹陷。另外，我們也確實發現有soft TO和 hard LO模的分裂現象，這兩者互相耦合造成分裂的現象，對鈦酸鍶鋇(x>0.7)的鐵電性質有嚴重的破壞性。

The objective of this report is to study the optical properties of BaxSr1-xTiO3 (BST) powders in the structural phase transition. The various ratios Ba/(Ba+Sr) of BST powders were synthesized by the sol-gel method. Their lattice constants were calculated from x-ray diffraction data. At room temperature, we find that BST powders have structural phase transition while x is close to 0.7, and the change of lattice constant didn’t obeyed to the linear Vegard law. Furthermore, there is a discontinuous around x = 0.4. By mean of the measurement of Raman scattering, the persistence of strong Raman line in BST while x<0.7(cubic) suggested the presence of significant disorder. The disappearance of Raman peak at 305cm-1、186cm-1 and 720cm-1 were happened with the structural phase transition (x 0.7). We find that the dip at 186cm-1, the A1(TO1) mode, is caused by the three A1 (TO) mode coupling effect. Additionally, we also observe the soft TO and hard LO splitting due to the Coulomb interation. The splitting has seriously destructive to the ferroelectric properties of BST powders.