Research On Composite Doped LaMnO₃ Ceramics

Doped LaMnO3 ceramics showed temperature dependent metal-insulator (MI) and paramagnetic-ferromagnetic (PM-FM) phase transition in certain conditions. After this transition, the property of infrared emissivity appears differently. When the temperature is above the transformation temperatures, the ceramics shows high infrared emissivity with good heat dissipation performance. However, when the temperature is below the transformation temperature, it shows reversely. Now, doped LaMnO3 ceramics has become the hot spot of intelligence thermal control materials at home and abroad because it could change its infrared emissivity according to the temperature.This paper explored the preparation of the doped LaMnO3 materials, and researched the crystal structure, mechanical property, infrared emissivity and phase transition temperature of the doped LaMnO3 materials in order to find the relationships among component, process, structure and performance. The study includes:(1)The synthesis process of high-purity powder of LaMn1-yBy03(B=Fe,Ti) and La0.825Sr0.175Mn1-yBy03(B=Fe,Ti). (2)The sintering process of high quality bulk of LaMn1-yByO3(B=Fe,Ti) and La0.825Sr0.175Mn1-yByO3(B=Fe,Ti). (3)Using XRD, SEM and related test equipments to test and analyze the crystal structure, density, hardness, microstructure, infrared emissivity properties and phase transition temperature of materials.The results show that:high quality bulk of doped LaMnO3 materials can be prepared by appropriate process; doping elements and doping influence the structure of materials; the crystal structure of LaMn1-yByO3(B=Fe,Ti) powder and La0.825Sr0.175Mn1-yByO3(B=Fe,Ti) powder are both Hexagonal R3m[160](a=b≠c, a=β=90°,γ=120°); the cell volume is direct ratio to lattice constant a and b, but has inverse ratio with lattice constant c; the cell volume and the lattice constant of doping at A and B site are smaller than those of doping at B site; in addition, the infrared emissivity and phase transition temperatures of LaMn1-yByO3(B=Fe,Ti) and La0.825Sr0.175Mn1-yByO3(B=Fe,Ti) materials in relation to the cell volume and lattice constants a, b, c of materials.