我们制备了名义成分是La1.4 Ca1.6 Mn2 O7的多晶样品,并且研究了它的结构、磁性和电性.利用Rietveld方法对X射线衍射数据进行精修的结果表明,该La1.4 Ca1.6 Mn2 O7是由钙钛矿锰氧化物La0.66 Ca0.34 MnO3和氧化钙CaO组成的复相混合物.其中,La0.66 Ca0.34 MnO3占相成分的大部分,而CaO占小部分.我们对比了该名义组分样品La1.4 Ca1.6 Mn2 O7和La0.7 Ca0.3 MnO3的铁磁居里转变温度和绝缘体-金属转变温度,结果表明该La1.4 Ca1.6 Mn2 O7的磁输运性质是由其中的钙钛矿相成分决定的.所有的这些结果表明,名义组分样品La1.4 Ca1.6 Mn2 O7实际上并没有形成所谓的Sr3Ti2O7型的双层结构,而实际形成的是以钙钛矿结构作为主相的复相混合物.
Polycrystalline sample with nominal composition La1.4 Ca1.6 Mn207 has been prepared and characterized by X-ray diffraction( XRD),as well as magnetic and electrical measurements.Rietveld refinement of the XRD pattern indicates that the La1.4Ca1.6 Mn207 sample is a multiphase mixture of doped perovskite manganite La0.66 Ca0.34 MnO3 as the majority phase and calcium oxide CaO as the minority phase.Both the Curie temperature and the insulator-metal transition temperature of the La1.4 Ca1.6 Mn207 sample are in consist with those of La0.7 Ca0.3 Mn03 sample,suggesting that its magnetotransport properties are dominated by the perovskite phase.All the results object to the literature reported before that the La1.4 Ca1.6 Mn2O7 samples form with a double-layered Sr3Ti207-type tetragonal structure.
参考文献
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