Gd3+掺杂钙钛矿锰氧化物(La0.9Gd0.1)4/3Sr5/3Mn2O7的磁性和电性研究*1

王 志 国,向 俊 尤,万 素 磊，武 柯 含，鲁 毅,赵 建 军

(包头师范学院 物理科学与技术学院，内蒙古 包头 014030)

1 实验方法

将原料La2O3、Gd2O3、MnCO3和SrCO3通过固相反应法合成(La0.9Gd0.1)4/3Sr5/3Mn2O7多晶样品。实验中所用的氧化物纯度都大于99.9%。充分混合研磨按比例称量的各组分氧化物，将研磨后粉末在1000℃下预烧12h。然后再将预烧后的粉末研磨并在相同条件下进行第二次预烧，最后，将两次预烧后的粉末研磨、压片。并将片状样品在1350℃煅烧24h并随炉冷却，最后，得到外观平整、坚硬而无裂痕的圆形块状样品。用X射线衍射仪检测样品的单相性。样品的磁化强度与温度的关系(M-T曲线)和电阻与温度的关系(R-T曲线)是通过美国Quantum Design公司设计的PPMS(the Physical Property Measurement System,PPMS-141)测量，测量温度范围为15K-300K。

2 结果与讨论

图1是(La0.9Gd0.1)4/3Sr5/3Mn2O7样品的X射线衍射图。其衍射图谱由Sr3Ti2O7和ABO3型钙钛矿相的衍射峰共同组成(ABO3相的衍射峰用箭头标出)，并且(105)和(110)峰的相对强度发生了变化，这表明样品是由Sr3Ti2O7和ABO3结构的相共同组成。由于在双层钙钛矿结构(La0.9Gd0.1)4/3Sr5/3Mn2O7中，离子半径较小的Gd3+会优先占据岩盐层的R位[10,11]，随着Gd3+的含量的增加，岩盐层内的失配效应和应力增加，这样会导致双层钙钛矿的结构不稳定，从而发生结构相分离生成无限层(ABO3)的钙钛矿相。

图1：室温下(La0.9Gd0.1)4/3Sr5/3Mn2O7的X射线衍射谱

图2：0.1T磁场下(La0.9Gd0.1)4/3Sr5/3Mn2O7样品的磁化强度随温度的变化关系，插图表示dM/dT与T的关系

图3:在温度范围内，(a)、(b)、(c)和(d)分别为样品的R-T曲线ln(R/T)—1/T曲线、lnR—1/T曲线和lnR—T-1/4曲线

3 结论

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