Electric Transport Properties And Doping Effect In The Layered Manganites (SrO)(La_2/3Sr_1/3MnO₃)_n

This dissertation is relation to SrO(La2/3Sr1/3MnO3)n the manganese oxides with RP structure. We mostly studied the structure and electrical transport properties, The major studies are listed below:The classes of magnetoresistance were introduced, the electron and crystal structure and the mechanism of double exchange of manganite pervosike related to colossal magnetoresistance have been summarized. More attention had also been paid to the advance in the study of RP structure manganite and grain system.The principle and process of sol-gel method were introduced. With sol-gel method a series of different grain size La2/3Sr1/3MnO3 sample were prepared. Based on the transport mechanism of solid state, the low temperature electrical transport mechanism of La2/3Sr1/3MnO3 sample had been given. When grain boundary was considered the mechanism became complexity. Magnetoresistance of La2/3Sr1/3MnO3 have been report.The condition of preparing pure bilayered manganites La4/3Sr5/3Mn2O7 with sol-gel method have been given after a lots of experimental and analysis, especially X-ray diffraction and resistance dependence on temperature. The difference of grain boundary between pervosike structure sample La2/3Sr1/3MnO3 and bilayered pervosike structure sample La4/3Sr5/3Mn2O7 were reported. Experimental shown that surface of sample had different properties with body. The electrical transport properties of La2/3Sr4/3MnO4 have been introduced briefly.a series of La4/3(Sr1-xBax)5/3Mn2O7(0≤x≤1) samples have been prepared and studied. Magnetoresistance and electrical properties have been reported. Abnormal electrical properties of sample with Ba ion high-substitution were analysis. Metal –insulate transition have been obviously shift by substituted La with Y ion.