La_(0.7)Ca_(0.3)MnO_3与Al复合体系电磁输运性质的研究

研究了具有庞磁电阻(CMR)效应的锰基钙钛矿氧化物La0.7Ca0.3MnO3(LCMO)与Al复合体系的电磁输运性质.根据X射线衍射分析及电阻率与温度的关系可知,在(1-x)LCMO+xAl(x代表物质的量)复合样品中,发现了新相Al2O3,且LCMO晶格常数和晶胞体积随Al掺量的增加而减小,同时在复合样品中出现了除对应LCMO本征金属-绝缘体转变峰TP1之外,在较低温度区域出现了另外一个转变峰TP2的现象,且复合样品转变峰TP2比LCMO本征金属-绝缘体转变峰TP1处于较宽的温度区域.经研究认为,在合成复合样品的实验过程中,既有Al被氧化为Al3+替代Mn3+的替代反应,也有Al经过高温与空气发生反应生成Al2O3,进而填隙在LCMO晶界处影响母体的电磁输运性质.本系列复合物中较宽温度区域CMR的发现为今后同类问题的研究提供了很好的实验基础.

The Study of Electrical-magnetic Transport Properties of La_(0.7)Ca_(0.3)MnO_3/Al Composites

The electrical-magnetic transport properties of manganese peroveskite oxides La0.7Ca0.3MnO3(LCMO) and Al composites have been investigated.According to the results of X-ray diffraction(XRD) and temperature dependence of the resistivity,and in(LCMO)1-xAlx composites(x represents the volume fraction),we find a new phase Al2O3,the unit-cell volume and the relevant structural parameters in peroveskite structure decrease with the increasing of Al content.The samples show that another I/M transition TP2 besides the one Tp1 corresponding to LCMO's intrinsic I/M transition.The new I/M transitions are at a lower temperature area and have a wider temperature region than the latter ones.Some Mn3+ substituted by Al3+ together with the new phase Al2O3 segregated at the grain boundaries of LCMO are the reason for above phenomena.The observation of CMR in wide temperature region offers a foundation for similar experimental research.