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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。
The La vacancies La_ (1-x) MnO_ (3 + δ) (0.04,0.1,0.15,0.2) polycrystalline samples were prepared by the solid-state reaction method and characterized by X-ray diffraction (XRD) and Raman spectroscopy Combined with the study of the regulation of the electronic transport properties by the microscopic crystal structure. X-ray diffraction results show that all samples have a rhombic structure, space group R3C. Raman spectroscopic studies show that the phonon vibrational peaks at 490 and 620 cm -1 are observed for each sample, which correspond to the anti-symmetric stretching modes and the symmetric vibration modes of MnO_6 octahedra respectively. With the increase of La vacancies and the decrease of temperature, the anti-symmetric vibration mode peaks all show hardening phenomenon, which indicates the enhancement of the coupling of lattice orbit-spin-phonon (OSP) and the intensification of Jahn-Teller distortion. The study of electrical transport properties shows that as the La vacancy concentration increases, the transition temperature of the metal insulator decreases and the magnetoresistance effect decreases. The results show that La vacancies lead to enhanced OSP coupling and Jahn-Teller distortion, which leads to poor conductivity of La_ (1-x) MnO_ (3 + δ).