Study On The Doped LaMnO₃ Ceramics

The doped LaMnO3 ceramics has been layed more emphasis as a new functional material. LaMnO3 ceramics at certain doping elements and levels showed temperature dependent metal-insulator (MI) and paramagnetic-ferromagnetic (PM-FM) phase transition. After this transition, the property of infrared emissivity appears differently. When the temperature is above transformation temperatures, the ceramics performs high infrared emissivity with good heat dissipation performance. However, when the temperature is below the transformation temperature, it shows reversely. It has been applied in the space shuttle. Using this kind of material can largely simply the thermal control system and achieve the active control.In this paper, the main research object is the alkali metal sodium, potassium, sodium and rare earth elements neodymium doped binary compound doped lanthanum manganese ceramic. The fabrication method is discussed systematically. The single phase of lanthanum manganese powder is produced through solid state reaction. And the bulk is also made by high-temperature sintering. After those, the density, hardness, curie temperature and infrared emissivity are detected. The chemical phase is tested by XRD as well. SEM was used to investigate the micro structure and EDS was used to analysis the constitution. Based on these mechanical and functional properties, the sintering temperature, holding time and the molding pressure are all optimized. In addition, a thin bulk sample showing good property, especially infrared emissivity, was made by mechanical process.The experimental results show that the initial factors influencing strength are molding pressure, Granulation process, sintering temperature and holding temperature and so on. Only finding out the suitable parameters, the ideal sample showing high strength can be made. Among these parameters, curie temperature plays a key role. It is found that curie temperature of La1-xNaxMn03 and La1-xKxMn increase with the rising of doping x. The curie temperature of Lao.8-xNdxNa0.2MnO3, with x between 0.1 and 0.6, decreases with high doping. Doping With different elements, the ceramic shows a similar trend of infrared emissivity which goes down when doping increases.After grinding mirror, infrared emissivity nearly becomes 0.15 time. Under waveband of 8-14μm, infrared emissivity is higher than that under waveband of 3-5μm.