Study On Self-polarization Behavior Of Ba²⁺-Ti⁴⁺ Doped BiFeO₃ Thin Films Prepared By Heat Treatment In Electric Field

Due to the asymmetry of the charge center,many electric dipoles are generated,and the electric dipoles with the same local orientation are formed in the ferroelectric thin film.The domain walls are formed between the domains and the domains.The directions of these domains are random in general.When the electric field are applied,spontaneous polarization occurs in the films and the domains tends to regular arrangement.However,the electrodes are not allowed to appear in many ferroelectric devices.On the other hand,the electric resistances of some ferroelectrics are very small and the coercive fields are large at roo m temperature,which can't make the ferroelectrics occur polarization by the means of applying electric field.And this kind ferroelectrics are easy to occur depolarization and the domains can't maintain regular arrangement for a long time.If the prepared ferroelectrics can form regular polarization spontaneously without applying electric field,it will be of great help in designing some ferroelectric heterostructures and devices.It is called the self-polarization behavior,which doesn't require any external excitation and the regular polarization state can spontaneous form.Among the many ferroelectric materials,bismuth ferrite?Bi Fe O 3?is the only one single-phase multi-ferrous material which has both ferroelectric and antiferromagnetic properties at room temperature.It has a suitable band gap?2.3².7e V?,a higher ferroelectric Curie temperature?about 850??,a larger residual polarization intensity and multi-iron characteristics,which is expected to be applied to ferroelectric random access memory,spin electronics,optoelectronic devices,multiferroic device and so on.In addition,bismuth ferrite doesn't have lead,which is a healthy and environmentally friendly ferroelectric materials.Therefore,we selected BiFeO₃ as the object to study its self-polarization behavior.In this paper,the BiFeO₃ thin films were prepared by sol-gel method.The annealing temperature,the effects of co-doping Ba²⁺-Ti⁴⁺ ions and secondary heat treatment on self-polarization behavior were investigated by analyzing the morphology,structure,phase,dielectric properties and ferroelectric properties of the films.In this research,the Bi_1-2x?BaTi?_xFeO₃ film with high crystallinity and high purity was successfully obtained under suitable precursor and preparation process and the optimum annealing temperature 600? for Bi_1-2x?BaTi?_xFeO₃ film was found.The co-doping by Ba²⁺-Ti⁴⁺ significantly improved the texture in the?010?direction of Bi_1-2x?BaTi?_xFeO₃ film and did not cause hetero phase and phase change.The films with high doping content obtained higher self-Build electric field strength.In contrast,the dopant brings more defects and carriers,which made the dielectric loss and leakage current density increase.The electric field heat treatment can improve the self-built electric field intensity in the direction of self-built electric field of Bi_1-2x?BaTi?_xFeO₃ thin film and reduce its leakage current.The external electric field broke the original domains walls of the film.The electric dipole in the direction of the electric field becomes the same electric dipole as the self-built electric field,and the partial electric dipole is cured by prolonging the temperature and the Bi_1-2x?BaTi?_xFeO₃ film Behavior.The preferential orientation of BiFeO₃ thin films in one direction is a prerequisite for the existence of self-built electric field,but it does not mean that the strength of self-built electric field is positively correlated with the strength of preferential orientation.The positive and negative current ratio are dire ctly related to the strength of self-built electric field.The more obvious of film's self-polarization behavior,the more stronger of self-built electric field and the positive and negative current ratio is greater.