【摘要】 研究了(Nd1-xLax)0.5Ca0.5MnO3(0≤x≤0.5)体系的X射线衍射谱,Raman吸收谱和电输运特性.通过电输运性质的测量给出了金属绝缘转变温度Tm与A位离子平均半径之间的关联.结果表明,La3+离子的掺杂压制低温下的电荷有序,导致金属绝缘转变开始出现,且随掺杂浓度的增加,金属绝缘转变(MI)温度(Tm)向高温区移动,对应的峰值电阻率ρp降低.X射线衍射谱和电输运特性均表明,La3+离子的掺入使得A位平均离子半径(〈rA〉)增大,导致局部晶格畸变减小.在掺杂量0.3≤x≤0.5的区域范围内,随着x的增加,双交换作用逐渐增强,有利于低温下铁磁态的形成.但热循环实验的研究结果表明,这种铁磁态属于亚稳态,在能量上反铁磁态比铁磁态更稳定.更多还原

【Abstract】 The properties of perovskite (Nd_ 1-xLa_ x)_ 0.5Ca_ 0.5MnO_ 3(0≤x≤0.5) compounds are systematically investigated by use of Raman spectra and resistivity measurements. It is found that the metal-insulator(M-I) transition temperature T_m is related to average ion size of A site. It is given that the La doping induces the M-I transition and the transition temperature T_m shifts to higher temperature with the increasing of the La 3+ doping content, while the relevant resistance peak ρ_p sharply decreases. All the Raman spectra and resistivity results indicates that the La 3+ doping increases the average ion size of the A site, which decreases the local distortion of the lattice. In the doping range of 0.3≤x≤0.5, with the increasing of x, the doping of La 3+ cation favors the formation of ferromagnetic state which is due to the strengthen of the double exchange interaction. However, the recycling experiment reveals that the ferromagnetic state here is a metastable state and the antiferromagnetic state is favored in the energy aspect.更多还原