Ag-doped (La,Sm)_0.7(Ca,Sr)_0.3MnO₃ Materials Prepared By Sol-gel Method And Their Electromagnetic Properties

The rare earth doped manganite RE_1-xAE_xMnO₃(RE,trivalent rare earth ion and AE,divalent alkaline earth metal ion)with ABO₃ perovskite structure is a kind of material with rich physical properties and great potential application prospect.The colossal magnetoresistance(CMR),temperature coefficient of resistance(TCR)and metal-insulator transition(MIT)found in this kind of materials are the main physical properties of their applications.Among them,the most typical material system is La_1-xCa_xMnO₃,whose TCR and MR are small,which hinders its practical application,such as infrared detectors,magnetic sensors and magnetic refrigeration devices.The main research content of this paper is to obtain specific materials with high TCR and MR by doping silver and rare earths.Because the silver doping can significantly improve the La_1-xCa_xMnO₃,the TCR,paper adopts silver doping which is different from the previous methods,specifically,silver is mixed in the form of ions when the gel is formed,so that the prepared materials have higher uniformity of particle size and smaller particle size than solid phase doping.In order to obtain the best silver doping process and doping amount,multi-series polycrystalline ceramics with different sintering temperature and initial addition of AgNO₃ were prepared.The optimum sintering temperature of La_0.67Ca_0.33MnO₃:yAg sample is 1450?,when the sample shows single perovskite structure,excellent crystal quality,uniform grain size,high Tp,low peak resistivity(?_max)and maximum TCR.After the sintering temperature was determined,the best doping amount of Ag was determined,and the electromagnetic properties of the samples with different silver doping amount(0?0.3mol)were analyzed and compared.the results showed that the TCRmax of La0.67Ca0.33MnO3:0.1Ag reached 60.45%K^-1,and the MR was greatly improved,that is,MR_max was 69.63%.In order to further improve the MR,of the material,the magnetic rare earth element Sm was studied to replace the La site,and a series of ceramic samples of La_0.7-xSm_xCa_0.3MnO₃:yAg(x=x=0.15,x=0=0.15)and La_0.7-xSm_xCa_0.2Sr_0.1MnO₃:yAg(x=0=0.25,y=0=0.10)were prepared successively.XRD results show that with the increase of the amount of Sm³⁺doping,the diffraction peak of the ceramic sample shifts to a high angle,and the refinement results show that the grain size decreases gradually.The test results of electrical transport performance show that with the increase of the doping amount of Sm³⁺,the Tp decreases and?_max increases,but TCR_maxand MR_max do not change monotonously.In the silver-doped LSCSMO:Ag system,both TCR and MR increased at first and then decreased,and reached the maximum at the same amount of Sm doping,that is,La_0.55Sm_0.15Ca_0.2Sr_0.1MnO3ve0.1AG,in which TCRmax=49.94%K^-1and MR_max=92.17%.In this paper,the material with high TCR and MR is obtained,which improves the development of the material in practical application to a certain extent.