Defects And Magnetic/Electrical Properties Of Fe-Doped CuFeO₂-Based Ceramics

Recently,CuFeO₂,a delafossite material with quasi two-dimensional hexagonal lattice structure,has attracted wide attention of researchers because of its unique magnetic structure and strong magnetoelectric coupling effect.However,the internal physical mechanism of CuFeO₂is complex,especially the magnetoelectric regulation mechanism which has attracted the most attention is still unclear and should be further explored.In this paper,several ions doped CuFeO₂samples were prepared by solid state reaction method,and X-ray diffraction spectrometer,Field emission scanning electron microscopy,Raman spectrometer,X-ray photoelectron spectrometer,positron annihilation spectrometer,physical property measurement system,impedance analyzer and other technologies were used to characterize and analysize the microstructure and physical properties and explore the correlation between them.The research contents and conclusions are as follows:1.Effects of series of rare-earth ions(La³⁺,Sm³⁺,Eu³⁺,Gd³⁺,Dy³⁺,and Ho³⁺)doping at Fe sites on the microstructure and magnetic properties of CuFeO₂.The results show that R doping increases the lattice parameters and improves the CFO systems’molecular polarizability.And R doping inhibits the grain growth and increases the density of the sample.Positron annihilation lifetime spectroscopy results demonstrate that the defect concentration,size and local electron density are greatly affected by R ion doping.The magnetic measurements reveal that the antiferromagnetic stability is influenced by R doping,which is ascribed to the effect of magnetic moments,variations in exchange interactions,and the partial reduction of spin frustration.The magnetization behaviors of the R-CFO samples are also influenced by doping ions,which is mainly explained by the different magnitudes of the R ions’magnetic moments.The local electron density n_eis associated with the maximum magnetization and plays an important role in regulating the magnetic properties of CFO ceramics.2.Effect of transition metal ions with different valence states doping at Fe sites on the microstructure and physical properties of CuFeO₂.The results show that M（Sc and Zr）doping leads to the increases of the lattice parameters and the decreases of grain growth.Positron annihilation lifetime results indicate that M doping increases the open volume and the concentration of defects,then decreases the electron density in annihilation sites.Furthermore,M doping decreases the magnetic temperatures and the magnetization.All samples show the giant dielectric property and low loss value within the measurment range.In addition,the dielectric constant and loss have good frequency stability at high frequency.3.Effect of non-stoichiometric Ti doping at Fe site on microstructure and physical properties of CuFeO₂.The results show that Ti doping increases the lattice parameters and produces more pronounced grain boundaries and denser microstructure.With increasing of Ti⁴⁺ions doping concentration,the grain size decreases.Ti doping leads to the formation of Fe²⁺and Ti³⁺ions.The Ti³⁺concentration decreases sharply with increasing Ti doping concentration.The Fe²⁺concentration fluctuates with variations in the Ti⁴⁺/Ti³⁺concentrations.In addition,the Fe²⁺concentration may be affected by the cation vacancy concentration in the samples.The positron annihilation lifetime spectroscopy results reveal that the open volume and the concentration of defects fluctuate owing to the competition between two opposite factors:the agglomeration of vacancy-type defects and structural distortion caused by Ti doping.Furthermore,Ti doping decreases the magnetic temperatures T_N1and T_N2and the magnetization.In addition,the magnetization exhibited a strong correlation with the Ti³⁺concentration and the defect characteristics.The undoped sample shows the giant dielectric property within the measurment range.In addition,the dielectric constant and loss have good frequency stability at high frequency.Through the above contents,the changes of microstructure and the influence of electromagnetic properties of CuFeO₂ system are studied,which provides an experimental basis for the study and application of physical property mechanism of strong correlation electronic system CuFeO₂.