Raman光谱研究La_(1-x)MnO_(3+δ)结构畸变对电输运性质的影响

Influence of Microstructural Distortion on Electrical Transport Properties of La_(1-x)MnO_(3+δ) Bulk by Raman Spectra

采用固相反应法制备了La空位La_(1-x)MnO_(3+δ)(0.04,0.1,0.15,0.2)多晶样品,利用X射线衍射(XRD)与拉曼光谱(Raman)技术相结合研究了微观晶体结构对电输运性质的调控。X射线衍射结果表明,所有样品都具有菱方结构,空间群为R3C。Raman光谱研究表明每种样品在490和620 cm^(-1)都观察到比较明显的声子振动峰,分别对应MnO_6八面体的反对称伸缩振动模式和对称振动模式。随着La空位的增加和温度的降低,反对称振动模式峰均出现硬化现象,表明晶格轨道-自旋-声子(OSP)耦合作用的增强及Jahn-Teller畸变加剧。电输运性质研究发现,随着La空位浓度的增加,金属绝缘体转变温度降低,磁电阻效应减小。研究结果表明La空位导致OSP耦合作用增强,Jahn-Teller畸变加剧,致使La_(1-x)MnO_(3+δ)导电性变差。

A series of La1-xMnO3 ＋δ（0.04, 0.1, 0.15, 0.2） polycrystalline samples were prepared by solid-state reaction. Combined X-ray diffraction with Raman spectra technology, the modulation of electrical transport properties by the microstructure was investigated. The results demonstrated that all the samples crystallized in the rhombohedral （R） structure, exhibiting R3C space group. Raman spectra showed that, the most intense peaks of all samples were observed around 490 and 620 cm^-1, which correspond to the antisymmetry stretching mode and symmetric stretching mode of MnO6 octahedron. With La-vacancies increasing and temperature ranging from 300 to 85 K, the antisymmetry stretching modes were both hardened, which indicates La-vacancies enhance the orbital-spin-phonon （OSP） coupling and Jahn-Teller distortion. The research on the electrical transport properties showed that, the metal-insulator transition temperature and magnetic resistance effect decreased, with increasing La-vacancy concen- tration. The investigation results demonstrated La-vacancies caused the enhancement of orbital-spin-phonon coupling and stronger Jahn-Teller distortion, resulting in the poor electroconductibility of La1-x MnO3＋δ bulk.