0.5Ca 0.5MnO 3 manganites]]>

摘要

Polycrystalline samples of La0.5?xYxCa0.5?ySryMnO3(0?≤?x?≤?0.20, 0?≤?y?≤?0.22) were synthesized by solid state reaction method. The degree of A-site disorder increases linearly with increasing doping content. Structural analysis of X-ray diffraction shows that samples crystallize in a pure orthorhombic Pnma phase and antisymmetry stretching appears in MnO6octahedron. Raman spectra illustrate rotationlike mode and antisymmetry stretching mode are both hardened with increasing A-site disordering, indicating the Jahn-Teller distortion strengthened. The metal-insulator transition temperature and MR values are found to decrease with increasing A-site disordering. The suppression of metallic behavior is ascribed to the enhancement of Jahn-Teller effect caused by increasing A-site disordering.