Preparation And Properties In Ce Doped Ca₂FeMoO₆ Double Perovskites

There has been a great deal of studies in double perovskites A₂BB'O₆(A= divalent cations;B=transition metals;B'=non-magnetic cations),since Kobayashi discovered the room-temperature low-field magnetoresistance and half-metallic properties in the compound Sr₂FeMoO₆ in 1998.In this paper,the crystal structure,microstructure,magnetic and transport properties have been investigated when doping the Ce³⁺ at A site.We used sol-gel method to prepare a series of double perovskites Ca_2-xCe_xFeMoO₆ samples and explored the preparation of the temperature and ventilation conditions.The X-ray diffraction (XRD),X-ray refinement method,Scanning electron microscope(SEM), vibrating sample magnetometer(VSM),superconducting quantum interference device(SQUID),and two-wires resistance measurement method were used to investigate the crystal structure,microstructure,magnetic properties and transport properties,respectively.The main conclusions are as follows:1.Our investigation indicates that the final annealling condition is quiet important to synthesize the pure samples.We have gained a series of pure Ca_2-xCe_xFeMoO₆(x=0,0.1,0.2,0.3,0.4) samples at 1000℃in appropriate ratio of H₂/Ar.In the study we found that the flux of H₂ increases with the increasing of x.2.The x-ray refinements show that the crystal structure of samples belongs to the monocline(a≠b≠c,β≠90°) with the space group of P2₁/n.The cell parameters and the anti-site defects are increasing with x,but there is no structure transition in all materials.3.The SEM patterns of Ca_2-xCe_xFeMoO₆ revel that the average grain size is around 2-5μm.The samples grow densely and have clear grain boundaries.4.The magnetic properties measurement results both in room-temperature and low-temperature(5K) indicate that M_S decreases with the increasing of x, which can be explained by the electron doping effect and the increasing of anti-site defects.The Curie temperature of Ca_2-xCe_xFeMoO₆ increases with the increasing of the Ce concentration,due to the enhancement of the exchange interaction between Fe-O-Mo by the electron doping effect. 5.With the increasing of x(0～0.6),the resistivity of Ca_2-xCe_xFeMoO₆ increases first,reaching the largest value at x=0.2,then decreases at a certain temperature.The Ca_2-xCe_xFeMoO₆(x=0～0.6) exhibits the metallic behaviour.However,the resistivity of Ca_1.2Ce_0.8FeMoO₆ sample decreases with the increasing of temperature,exhibiting semiconductor-like behaviour.