Perovskite La_x(Ca,Sr)_1-xMn_y(Cr,V)_1-y Microstructure, Electrical Transport Properties And Magnetoresistance Effect Of Sub>O₃

The perovskite manganite La_1-x(Ca,Sr)_xMnO₃exhibits rich physical properties,e.g.,colossal magnetoresistive(MR)effect,metal-insulator(M-I)transition,due to coupling among multiple degrees of freedom,such as charge,spin,lattice and orbital orderings.Therefore,it has the potential to be used in high pergormance infrared detector,magnetic sensors,the detector and other devices.However,the lower MR and temperature coefficient of resistance(TCR)at room temperature limits La_1-x(Ca,Sr)_xMnO₃'s practical application.This paper focus on the effect of(Cr;V)substitution on the crystal structure,surface morphology and electrical transport properties of ceramic La_1-x(Ca,Sr)_xMnO_3.In this paper,the(Cr,V)doped La_1-x(Ca,Sr)_xMnO₃ceramics were synthesized by sol-gel method.The physical properties of the samples were characterized.The results shows that Cr and V existed in La_1-x(Ca,Sr)_xMnO₃with valence+3 and+5,respectively.All samples illustrated perovskite structure.The slight amount of the elements substituting for Mn doesnot modify the perovskite structure,but distort the crystal structure by affecting Mn-O-Mn bond angle and Mn-O bond length.As the amount of Cr;V doping in La_0.825Sr_0.175Mn O₃and Cr doping in La_0.7Ca_0.3MnO₃increases,the growth of the grain is suppresses.As the V doping in La_0.7Ca_0.3MnO₃the growth of the grains is promoted.With the increase of doping amount of elements(Cr,V)at the Mn-site in the two series,the metal-insulator transition of the sample shifts to the lower temperature,meanwhile the resistivity increases.The change of these properties is mainly attributed to the fact that the doping of the elements changes the grain boundary effects and double exchange interaction.The proper amount of doping Cr and V in La_0.825S_r0.175MnO₃and the slight amount of Cr doping in La_0.7Ca_0.3MnO₃can improve the peak of TCR and MR.The change of these properties is mainly attributed to the fact that the doping of the elements changes the ratio of Mn³⁺/Mn⁴⁺,and affects the double exchange interaction,Jahn-Teller effect and carrier density in the system.Doping V in La_0.7Ca_0.3MnO₃can reduce the TCR and MR,but broadens the sensitive region of MR and TCR,This is mainly caused by the presence of multiple ferromagnetic phases in the sample due to the doping of V.