The Structure And Electrical Properties Of Doped YbMnO₃

Rare earth manganese oxide?RMnO₃?has attracted much attention due to the properties of magnetoresistance,multiferroics and so on.Most of the related research is focused on material with R = La-Sm.For RMn O₃ with small radius,the synthesis of the the orthorhombic phase is under high pressure and high temperature,so the relevant research is little.In this paper,YbMn O₃ was selected as the object of study,and the structure of the material was adjusted by doping Ca at the A site and Ga at the B site.The effect of doping on Jahn-Teller effect was analyzed by structural refinement and infrared spectroscopy.At the same time,the resistance,dielectric and magnetic properties of the system after doping are tested and the reason of the change of the property is analyzed.YbMn_1-xGa_xO₃ was prepared by solid-phase reaction at 1350 ?.The product is hexagonal.However,when the doping amount reaches 0.4 and 0.5,Yb3Ga5O12 appears as impurity.The result of the structural refinement displays that with doping,lattice constant c increases,while a and b decreases.At the temperature from 77 K to 400 K,under the test frequency of 1k Hz,10 k Hz,100 k Hz,1MHz,the relative dielectric constant is about 101 to 102,which is not high.The samples obtained by the solid phase method were treated under the conditions of 4GPa and 1000 ?,and the hexagonal phase was successfully converted into the orthorhombic phase,but the Yb3Ga5O12 impurity still exists.With Ga-doping,the lattice constant a and b decrease,while c increases;the lattice distortion becomes smaller.Jahn-Teller effect becomes weaker.As a result,Mn-O-Mn bond angle becomes weak.Ga³⁺-doping reduces the antiferromagnetic transition temperature of YbMn O₃ system to less than 20 K.The dielectric coefficient of the orthorhombic phase YbMn_1-xGa_xO₃ is much larger than that of the hexagonal phase.The orthorhombic phase Yb_1-xCa_xMnO₃ was synthesized by 4GPa and 1000 ?.Ca2+-doping introduces Mn4+,witch weakens the Jahn-Teller effect of the system.With the increase of Ca-doping,the lattice constant b decreases,while a and c increase,the unit cell volume decreases and changes greatly in the doping interval of 0.2-0.3.The results of SEM show that the crystallinity are better than those of solid phase method after high pressure and high temperature.The resistivity decreases with the Ca2+-doping and follows the thermally activated conduction mode.Ca2+-doping in orthorhombic YbMn O₃ reduces the anti-ferromagnetic transition temperature of the system.The infrared spectrum shows that Mn-O-Mn bond angle increases with doping.