Hydrothermal synthesis,sintering and characterization of nano La-manganite perovskite doped with Ca or Sr

Two lanthanum manganite perovskite-nanostructures, namely; La_xCa_(1-x)MnO₃ and La_xSr_(1-x)MnO₃ (x?=?0.1, 0.3, 0.5 and 1.0), were synthesized by hydrothermal method. To follow up the composition of formed phases, the synthesized powders were calcined at different temperatures. The obtained materials were investigated by X-ray diffraction (XRD) and transmission electron microscope (TEM). Moreover, the calcined powders were pressed at 100?MPa and sintered at variable temperatures; i.e. 1250, 1300, 1350 and 1450?°C. The phase composition and microstructural characteristics of sintered pervoskites were examined by XRD and scanning electron microscope (SEM). Furthermore, physical (bulk density and apparent porosity), electrical resistivity and magnetic properties were also determined. The results revealed that La_xCa_(1-x)MnO₃ and La_xSr_(1-x)MnO₃ nanostructures were successfully prepared by hydrothermal method. The physical properties of sintered pervoskites were strongly depended on dopant type and concentration. The maximum sintering temperature for La_xCa_(1-x)MnO₃ was 1400?°C while for La_xSr_(1-x)MnO₃ was 1450?°C, after which the materials have been fused. Materials doped with Ca or Sr exhibited lower resistivity. On the other side, the magnetic properties have been also improved after addition of Ca or Sr. This has been discussed based on the double exchange mechanism. La_xSr_1-xMnO₃ exhibited better magnetic properties than La_xCa_1-xMnO₃ and LaMnO₃. La_0.5Ca_0.5MnO₃ and La_0.5Sr_0.5MnO₃ exhibited the highest magnetization among the other pervoskites.