Research On Structure And Properties Of Perovskite Oxide Nd 0.5 Sr 0.5 Mno 3 And Its Doping System

The Nd_0.5Sr_0.5MnO₃ sample and Nd/Pr_0.5Sr_0.5Co_1-xMn_xO₃ ( 0≤x≤1 ) doping samples were synthesized by the the solid reaction method in this thesis. X-ray diffraction and Rietveld refinement were used to analyze crystal structure. Magnetic, electric transport and thermal properties of the samples were studied. The resualts show that:The Nd_0.5Sr_0.5MnO₃ sample was single-phase orthorhombic, and its space group belongs to Imma; With the temperature decreasing, secondary transformation of paramagnetic to ferromagnetic state takes place at T≈TC, meanwhile heat capacity changes, which demonstrats the short-term relaxation behavior of glasses with a attenuation cycleÏ„0≈30 min. When the temperature stays at TN≈TCO, it undergos ferromagnetic to antiferromagnetic state and charge-ordering transition at the same time, with crystal structure changing. When the temperature dereases to TN or below TN, it is indicated by the resistivity rate variation and magnetization curves of different temperatures that the sample is CE type charge-ordering phase with the coexistence of ferromagnetic phase and anti-ferromagnetic phase. As the temperature continues to decline, the increase in Magnetization at low temperature≈5 K, as well as M5 K(H)≥M50 K(H)at high magnetic field, indicate that Nd3+ is magnetic order at low temperature.In Nd_0.5Sr_0.5Co_1-xMn_xO₃(0≤x≤1)doped samples, the refinement results show that all samples are single-phase orthorhombic (Imma). The lattice constants a, b, c, crystal lattice average distortion ration D and the effective magnetic momentμeff increase with the Mn content, therefore Co3+/Co4+ transit into high-spin state, and all Co ions were high-spin state when x≥0.6. For substitution Mn of Co, the Mn-O-Co interaction is antiferromagnetic super-exchang, competing with the ferromagnetic double-exchange interaction Co³⁺-O^2--Co⁴⁺ and Mn3+-O2--Mn4+,which destroys the metallic behavior and exhibits semiconductor behavior when x≥0.2.The Pr_0.5Sr_0.5Co_1-xMn_xO₃(0≤x≤1)doped samples and the Nd_0.5Sr_0.5Co_1-xMn_xO₃(0≤x≤1)doped samples show almost the same properties. However, when x=0.4 and 0.6, the Temperature-Magnetization curves of both samples show abrupt break respectively at 75 K and 105 K, even if both samples are also ferromagnetic behavior, which is perhaps relative with the change of micro magnetic structure.