Crystal Structures And Properties Of Perovskite Lamno₃ And Its Doping System

The 21^st century is considered as a great surge in researches on perovskite materials,as more and more people are fascinated by its electromagnetic properties,such as magnetoresistance and electrical transportation.In this paper,by doping LaMnO₃ perovskite oxides at the A and O sites,we analyzed the crystal structure,magnetic properties and electrical properties of La_1-x-x Ca_x MnO₃ series,La_1-x-x Ca_x Mn?O,N?₃ series,La_0.67Ba_0.12Ca_0.21MnO₃ and La_0.67Ba_0.33MnO₃ samples,and reached conclusions as follows:Both the La_1-x-x Ca_x MnO₃ and La_1-x-x Ca_x Mn?O,N?₃ series belong to the orthorhombic system and the Pnma space group.When other factors remain unchanged,with the increase of Ca doping amount,the unit cell parameters and cell volume of the samples decrease,the Mn-O bond length shortens,and the Mn-O-Mn bond angle increases gradually.At the same time,the magnetization of the samples increases,the resistivity decreases,and the activation energy?E_A?decreases.Samples of both series show paramagnetism at ambient temperature or above,their Curie temperature?T_C?is lower than ambient temperature,and their conduction mechanism accords with the non-adiabatic small polaron conduction model.By comparing the La_0.7Ca_0.3MnO₃ and La_0.7Ca_0.3Mn?O,N?₃ samples,we found that after doping a certain amount of N,the cell volume of the samples decreases,the Mn-O bond length increase,the Mn-O-Mn bond angle decrease,and the number of single electrons decreases.During the process of N doping,the magnetic properties reduce while the resistivity increases.La_0.67Ba_0.12Ca_0.21MnO₃ belongs to the orthorhombic system and the Pnma space group,while the crystal structure of La_0.67Ba_0.33MnO₃ changes,which belongs to the rhombohedral system and the R-3C space group.With the increase of Ba doping amount,the unit cell volume increases,the Mn-O-Mn bond angle increases slightly,and the tolerance factor increases.La_0.67Ba_0.33MnO₃ particularly has a tolerance factor close to 1,and its magnetism is the strongest.La_0.67Ba_0.12Ca_0.21MnO₃ is quasi-paramagnetic.While La_0.67Ba_0.33MnO₃ is ferromagnetic,which shows obviously increase in magnetism and a magnetic phase transition at its T_C of 375.4 K.The sample conforms to the mean field theory and shows a second-order magnetic phase transition.La_0.67Ba_0.12Ca_0.21MnO₃ is semiconductive and fits in the non-adiabatic small polaron conduction model.And through the fitting of the metallic conductor part of La_0.67Ba_0.33MnO₃,we saw the main factor of its resistance is the scattering effect of double magnon,while the electrical transport mechanism of its semiconductor part at high temperature conforms to the small polaron variable range transition conduction model.