Preparation And Preparation Of La_1-xA_xMnO₃ (A=Ag,Na,K...) Polycrystalline Ceramics First-principles Research

The La_1-xA_xMn O₃perovskite manganese have important research value on sensitive devices such as infrared detection materials and radiant heat measurement,because of the steep metal-insulator transition characteristics,adjustable metal-insulator transition temperature(T_p),high resistance temperature sensitivity coefficient(TCR)and so on.Based on previous works,divalent alkali metal elements(A=Ca,Sr,Ba...)doped La_1-xA_xMn O₃as infrared detection material to obtain room temoerature for T_por improve the TCR value.Compared with divalent alkali metals,the doping of monovalent cations such as Ag,Na,and K on the physical mechanism,especially the transition of electrons between Mn³⁺and Mn⁴⁺is more obvious.monovalent cation-doped La_1-xA_xMn O₃(A=Ag,Na,K...)materials have been paid more attention to the preparation of magnetic refrigeration materials,but less research has been done on the application of infrared detection device materials.Therefore,this article mainly prepares monovalent cation La_1-xA_xMn O₃(A=Ag,Na,K...)polycrystalline ceramic materials based on the performance characteristics of monovalent cations Ag,Na,K and other materials that can improve the T_pvalue and TCR value of La_1-xA_xMn O₃,First-principles calculations of the Ag1-doped La_1-xA_xMn O₃crystal structure were performed.The main purpose is to obtain infrared detection materials with high TCR values??at room temperature.Therefore,the main content of this paper is to study how to improve the T_p(metal-insulation transition temperature)and TCR(temperature coefficient of resistance)of materials.The structure,morphology and properties were confirmed by X-ray diffraction,Scanning electron microscopy,X-ray Photoelectron Spectroscopy,Inductively coupled plasma mass spectrometry and so on.1.La_1-xAg_xMn O₃(x=0?0.5)(LAMO,x=0?0.5)polycrystalline ceramic samples prepared by the sol-gel method at a sintering temperature of 1100 and a sintering time of 12 h.As the doping component x increases,the metal Ag phase and the Mn₃O₄phase gradually begin to precipitate in the sample.At a sintering temperature of 1100,the maximum molar ratio of LAMO to Ag is 30%.As x increases,the T_pvalue of the sample gradually increases,T_pvalue reaches 291 K at x=0.5,TCR value is 8.58%,and LAMO polycrystalline ceramic material with excellent performance is obtained,which is the practical application of uncooled infrared detection devices provide theoretical explanation for reasearch.2.The Na-doped La_1-xNa_xMn O₃(LNMO,x=0?0.5)polycrystalline ceramic samples were tested and characterized.With the increase of Na doping,the sample grains gradually increased and the grain boundary scattering effect decreased.At the same time,Na doping improves the double exchange effect inside the material and reduces the Jahn-Teller(JT)effect.On the other hand,the T_pvalue of the material increases first and then decreases with the increase of Na doping.When x=0.3,the T_pvalue reaches a maximum of 318.9 K.For x=0.4,LNMO ceramic samples with a large TCR value of 6.47%were obtained.Then,in order to further improve the properties of the material,Na-doped La_0.7Na_xAg_0.3-xMn O₃(LNAMO,x=0?0.2)polycrystalline ceramic samples were prepared.By adjusting the Na/Ag co-doping ratio,ceramic samples were obtained at room temperature of 297 K and a TCR value of 10.4%.With the increase of the doping component x,all the samples have a single-phase perovskite oxide structure,the crystal grains within the crystals gradually increase,and the number of grain boundaries decreases,resulting in a decrease in the scattering effect of the grain boundaries,and thus the electromagnetic properties of the material Have an impact.The T_pvalue increases with increasing x,while the resistivity decreases first and then increases.At x=0.1,La_0.7Na_0.1Ag_0.2Mn O₃polycrystalline ceramic material with excellent performance at room temperature 297K and high TCR value of 10.4%was obtained.3.In order to advance and expand the types of monovalent cation doping,K-doped La_1-xK_xMn O₃(LKMO,x=0?0.4)polycrystalline ceramic materials were further prepared by experiments,and the electrical properties of the materials were improved by adjusting the K-doped component x.With the increase of the doping component x,the unit cell volume of the material increases first and then decreases,reaching a maximum when x=0.2.At the same time,the resistivity value showed the opposite trend,and the resistivity value reached the minimum at x=0.2.With the increase of x,the T_pvalue first increases and then decreases,reaching a maximum value of 277 K at x=0.2.Although experimentally obtained a higher TCR value(TCR_max=7.50%),the temperature is far from room temperature.In the final experiment,LKMO polycrystalline ceramics with a temperature of 261 K and a TCR value of 7.50%were prepared,which will provide a reference for the subsequent research of monovalent cation-doped LKMO materials.