Study On Properties Of Doping At La And O Sites In Perovskite LaMnO₃

A series of La1-xSrxMnO3(0.15≤x≤0.3) and La1-xSrxMnO3-yNy(0.15≤x≤0.3) samples havebeen prepared by conventional reaction processing. The structure, electrical transport andmagnetic properties have been studied by X ray powder diffraction, electrical resistivitymeasurement and vibrating sample magnetometer (VSM), respectively. The main results ofthis works are as follow:1. The crystal structures of perovskite La1-xSrxMnO3(0.15≤x≤0.3) series samples allbelong to trigonal system and their space groups are all R-3c. Through the respectivelyrefinemented pictures by Fullprof software, we know that the series samples’ experimentalvalue and the theoretical accord with relatively good. The lattice volumes decrease graduallywith the content of Sr approaching to33%. At x=0.33point, the magnetic of the sample isstrongest because of the most obvious double exchange interaction. Therefore, when the valueof x increases from0to0.33, the magnetization of the sample is increased significantly, andthe magnetic is enhanced. The magnetic moment of samples which show ferromagneticdecreases with the temperature becoming larger in the range of81K to300K. There will becertain changes of the electrical properties of the series of samples with Sr incorporationnearly33%. When we have a low level of Sr-doped, for example15%Sr-doped, the electricalproperties of the sample changes from metallic conductive to semiconducting behavior. Whenwe have a higher level of Sr-doped, for example30%Sr doped, the electrical properties ofthe sample shows metallic conductive behavior in a wider temperature range. Overall, theseries of samples have excellent magnetoresistance.2. The crystal structures of perovskite La1-xSrxMnO3-yNy(0.15≤x≤0.3) series samples allbelong to trigonal system and their space groups are all R-3c. Through the respectivelyrefinemented pictures by Fullprof software, we know that the series samples’ experimentalvalue and the theoretical accord with relatively good. The lattice volumes decrease graduallywith the content of Sr increasing to0.33. The magnetic moment of samples which showferromagnetic decreases with the temperature becoming larger in the range of81K to300K.At x=0.33point, the magnetic of the sample is strongest because of the most obvious doubleexchange interaction. Therefore, when the value of x increases from0to0.33, themagnetization of the sample is increased significantly, and the magnetic is enhanced. Themagnetization of the samples is greater than the series of samples’ which are not doped N. The law of the electrical properties of the series of samples is similar to the samples’ whichare without N doped. When we have a low level of Sr doped, for example15%Sr doped,the electrical properties of the sample changes from metallic conductive to semiconductingbehavior. When we have a higher level of Sr doped, for example25%,30%Sr doped, theelectrical properties of the sample shows metallic conductive behavior only. Moreover, afterincorporation of N, the magnetic increases while the resistance decreases. Theelectromagnetic properties improved significantly.