Study On Infrared Emissivity Of Lanthanum-Manganese Oxide In Infrared Field

As a new type of active thermal control materials,lanthanum manganese oxide with the metal-insulation phase transition phenomenon and variable emissivity characteristics has been widely focused by the researchers.The metal-insulating phase transition of the doped lanthanum manganese oxide belongs to the secondary phase transition.The reaction is not accompanied by the absorption and release of heat.The variable emissivity of the lanthanum manganese oxide takes place with the external field energy.Unfortunately,there has been no report on the effect of external field on lanthanum manganese oxide.Based on this,this paper chooses strontium-doped lanthanum manganese oxide as the research object to study the interaction between infrared radiation field and lanthanum manganese oxide,using X-ray diffraction analysis,scanning electron microscopy,infrared absorption spectroscopy,electron spin resonance and other modern means of analysis.The relationship between the composition,the structure and the emissivity of the lanthanum manganese oxide is explored,and the response characteristics and the law of the emissivity and the infrared radiation field are revealed.The conclusions are as follows:1.In order to overcome the deviation of emissivity test caused by radiation field,a radiation field system and a temperature control system are provided on the basis of the existing emissivity testing system.The device has the advantages of simple structure and low cost,which can significantly reduce the temperature difference between tested sample and standard sample.2.Lanthanum manganese oxide in the absence of external field: the crystals of the sample shrink along a and b axes and expand along the c axis with doped Sr,which may be one of the reasons for the decrease of emissivity of the sample.The order of emissivity values of different microscopic samples is: block>spherical>sheet.With the addition of Sr ions,the crystal integrity of the sample increases,the lattice vibration requires higher energy,the absorption peak of Mn-O bond is shifted to the short wave direction,and the absorption peak of x=0.3 sample is weaker than that ofother samples.So the emissivity shows a minimum.3.Under the action of infrared radiation field: the symmetry of the lattice structure and the stability increase with the temperature.The x=0.2 sample has a tendency to transform to the cubic phase,and its ferromagnetism is also enhanced.As a result of resonance between Mn-O,Mn-O-Mn,La-site vibration and infrared radiation of 2.5-500 ?m,temperature of the sample in the 2.5-500 ?m radiation field is higher than that in 0.76-2.5 ?m.And the emissivity of lanthanum manganese oxide under the same conditions is proportional to the wavelength,so emissivity of the sample in the 2.5-500 ?m radiation field is higher.At the same time,emissivity of x=0.2 sample in the radiation field of 2.5-500 ?m is lower when the radiation time is less than 20 s,and that in 0.76-2.5 ?m is basically unchanged.In the radiation field of2.5-500 ?m,the emissivity of x=0.2 sample increased by 23 %.The reason for this phenomenon may be related to the lattice vibration and the resonance absorption of the radiation wave,and the temperature position of the metal insulation phase transition as x=0.2.The emissivity of the samples showed an increasing trend in the radiation field and as same as temperature field.However,the emissivity of the sample at the radiation field is greater than that at the temperature field.The reason for the analysis is that the rise of emissivity in the radiation field is caused by two factors: one is the temperature rise caused by the radiation;the other is the change of the crystal lattice within the sample caused by the radiation.4.The influence of lattice vibration and energy level transition is more significant,and the influence of propagation process is relatively weaker.The resonant absorption band changes with the lattice structures,which affects the emissivity of the sample.The energy level transition within the sample can affect the absorption of light energy,which together with the lattice vibration,impact of sample emissivity.When the radiation distance of the sample is equal,the radiation band has little effect on the emissivity of the sample.