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用固相反应法制备了La(1-x)2/3Ca1/3MnO3(V-LCMO)和(La(0.7-x)Y0.3)2/3Ca1/3MnO3)(V-LYCMO)(x=0,0.02,0.04,0.08,0.10)系列La空位锰氧化物样品。X射线衍射(XRD)分析表明:所有的样品均为单相,具有正交对称性(Pnma)。La(1-x)2/3Ca1/3MnO3系统和(La(0.7-x)Y0.3)2/3Ca1/3MnO3系统的晶格参数以及Mn—O键长和Mn—O—Mn键角随La空位浓度不同而改变,说明在室温系统中存在Jahn-Teller效应。对于V-LYCMO系统,其晶格参数、Mn—O键长和Mn—O—Mn键角都比V-LCMO相应的值更小,这可能与离子半径小的Y3+部分替代La3+导致更大的晶格畸变有关。V-LCMO系统随着空位浓度的增大,绝缘体金属的转变温度TMI几乎不变。在x=0.04时MR值在温度TMI处达到最大值,约为220%(8T)。而对V-LYCMO系统,其转变温度TMI约为50 K,在温度40~50 K左右最大的磁电阻值超过106%。认为很大的磁电阻效应与用离子半径小的Y部分替代离子半径大的La有关,它会破坏双交换作用,从而导致Jahn-Teller效应。
La (1-x) 2 / 3Ca1 / 3MnO3 (V-LCMO) and (La (0.7-x) Y0.3) 2 / 3Ca1 / 3MnO3) (V-LYCMO) were prepared by solid- , 0.02, 0.04, 0.08, 0.10) series La vacancy manganese oxide samples. X-ray diffraction (XRD) analysis showed that all the samples were single phase and had orthogonal symmetry (Pnma). The lattice parameters of the La (1-x) 2 / 3Ca1 / 3MnO3 system and the (La (0.7-x) Y0.3) 2 / 3Ca1 / 3MnO3 system as well as the Mn-O bond length and Mn- The vacancy concentration varied from room temperature to room temperature, indicating that there is Jahn-Teller effect in the room temperature system. For the V-LYCMO system, its lattice parameter, Mn-O bond length and Mn-O-Mn bond angle are both smaller than those of V-LCMO, which may be due to the substitution of La3 + for the Y3 + Lattice distortion related. V-LCMO system with the vacancy concentration increases, the insulator metal transition temperature TMI almost unchanged. At x = 0.04, the MR value reaches a maximum at the temperature TMI of about 220% (8T). The V-LYCMO system, the transition temperature TMI is about 50 K, at a temperature of about 40 ~ 50 K maximum magnetic resistance value of more than 106%. It is believed that the large magnetoresistance effect is related to the substitution of the Y ion with a large ionic radius for La, which has a large ionic radius, which undermines the double exchange effect and leads to the Jahn-Teller effect.