显微拉曼研究外延生长的BaTiO3-x薄膜的结构相变与结构动力学

摘要

Structure dynamics of strongly reduced epitaxial barium titanate (BaTiO3-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 BaTiO3-x thin films. As the oxygen pressure decreases, the oxygen deficiency increases. When deposited under 3.0×10-5 Pa, the oxygen deficiency in BaTiO3-x film is 0.48, and tetragonal perovskite structure can be maintained even in this sample. Raman spectra confirm that BaTiO3-x thin films are in tetragonal phase with some deviated features. Moreover two weak peaks in Raman spectra of BaTiO0.52 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 BaTiO3-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 BaTiO3-x lattice structure. Because of the two-dimensional tensile strain imposed on the film by the substrate, the phase transition characteristics for bulk BaTiO3 are absent in the films over the temperature range of 78 to 550 K.%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10-2到10-5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3.0×10-5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550K的温度范围内不存在.