正离子尺寸离散度对混价锰氧化物中相分离的影响

the phase separation in manganites Ln1-xAxMnO3 is studied by cation replacements. The experimental methods include X-ray-diffraction; M-T, M-H and R-T dependences; and magnetic relaxation etc. The similarity of manganites and rare-earth alloys in magnetic and electrical transport properties is specially concerned. Two kinds of phase separation are identified, namely, (1) The electronic phase separation: components of a compound are located at the boundary of metal-insulator transition, the ferromagnetic clusters with nanometer scale have a higher carrier density. The case is similar to the competition between ferromagnetic and antiferromagnetic phases in the Gd-Dy-Nd alloys. Temperature and applied fields can control the ratio of two kinds of clusters, and the transform between the two phases is reversible, such as that in La0.5Ca0.5MnO3. (2) The phase separation introduced by disorder: the coexisting metallic and insulating clusters have the same carrier density. The corporation interaction makes the scale of a certain kind of clusters increase up to ~1μm. The first order transition has a percolation behavior, such as that in La0.625-yPryCa0.375MnO3. Besides, a parallel model of metallic and insulating channels can explain the peak of electrical resistance in La0.7Ca0.3MnO3.

相分离研究对于理解复杂氧化物系统中各种相互作用之间的竞争具有重要科学意义。对于钙钛矿结构锰氧化物，相分离发生于高掺杂的样品中。为了研究离子无序对相分离的影响，本项目将制备全新系列样品，通过元素替换改变A格点离子尺寸的离散度，但保持平均离子半恫槐洹＝ü挪饬亢凸獾绲嫉仁笛檠芯坎牧系奈镄裕喙泊嫣峁┬轮ぞ荨