显微拉曼研究外延生长的BaTiO_(3-x)薄膜的结构相变与结构动力学(英文)

Micro-Raman Investigation of Structure Dynamics and Structural Phase Transitions in Strongly Reduced Epitaxial BaTiO_(3-x) Films

我们用显微拉曼、卢瑟福背散射谱、X射线散射和非对称摇摆等实验手段研究了在1 0 - 2 到1 0 - 5帕氧气压下用激光分子束外延技术生长的BaTiO3-x薄膜的结构动力学特性。测量结果表明生长氧压越低,晶格常数c和c/a越大,晶格常数a稍微减小,晶胞体积变大。随着生长氧压的减小,薄膜中氧含量减小。在3 0×1 0 - 5帕氧气压下生长的薄膜中氧缺陷可达0 48,但是样品的四方相结构可以很好的维持。显微拉曼研究进一步确定了样品都是四方相结构。另外,在BaTiO2 52 薄膜的拉曼光谱中发现高频段有两个新峰,其可能是由于氧缺陷导致的二级拉曼散射引起的。随着生长氧压的减小,拉曼峰向低频移动,表明薄膜中的应力减小。同时,拉曼峰变宽,这可能是由于氧缺陷导致的结构畸变引起的。由于在薄膜中存在二维张应力,BaTiO3单晶样品中的结构相变特征在我们的样品中从78到5 5 0K的温度范围内不存在。

Structure dynamics of strongly reduced epitaxial barium titanate (BaTiO_(3-x)) thin films were investigated by Micro-Raman scattering technique, Rutherford backscattering spectrometry, X-ray diffraction, and asymmetric rocking curves. The results indicate that lattice parameters c and c/a ratio increase while a slightly decreases with decreasing oxygen pressure, indicating increased lattice volume of BaTiO_(3-x) thin films. As the oxygen pressure decreases, the oxygen deficiency increases. When deposited under 3.0×10^(-5) Pa, the oxygen deficiency in BaTiO_(3-x) film is 0.48, and tetragonal perovskite structure can be maintained even in this sample. Raman spectra confirm that BaTiO_(3-x) thin films are in tetragonal phase with some deviated features. Moreover two weak peaks in Raman spectra of BaTiO_(0.52) thin film were observed, and maybe induced by second-order two-phonon processes. Raman peaks shift towards lower frequency with a decrease in deposition oxygen pressure, suggesting that the stress in BaTiO_(3-x) thin films decreases, in the meantime the Raman peaks become broader which may attributed to a higher degree of structural disorder in strongly reduced BaTiO_(3-x) lattice structure. Because of the two-dimensional tensile strain imposed on the film by the substrate, the phase transition characteristics for bulk BaTiO_3 are absent in the films over the temperature range of 78 to (550 K.)