Investigation Preparation And Properties Of B-site Low-valence Substituted BiFeO₃ Thin Films

BiFeO₃?BFO?,as a multiferroic material,attracts the attention of researchers due to its excellent ferroelectric,piezoelectric and ferromagnetic properties that can be used in ferroelectric random access memory,microelectromechanical systems,and smart devices.At present,because of the existence of(_OV_2-)^?,valence state fluctuation of iron,and some defects in BFO films,the leakage current is too large,which has been the bottleneck of its development.In recent years,researchers have made a lot of attempts to improve their performance according to the affecting factors,including improving the preparation process and ion doping.The ion doping is proved to be the most effective method to improve the performance of the film.In this paper,BFO based thin film samples were prepared by sol-gel method,and the following conclusions were obtained through research.1?The concentration of precursor solution has a great influence on the properties of the film.0.3mol/L is the best concentration of BiFe_0.98Mn_0.02O₃?BFMO?thin films.P-E hysteresis loop indicate that the BFMO film with 0.3mol/L has the maximum double remnant polarization?2P_r?,which is 149.3?C/cm² at tested electric field of 1026 kV/cm.The BFMO film with 0.3mol/L has the minimum leakage current density which is 9.8×10^-8 A/cm² at tested electric field of 300 kV/cm,and the current conduction mechanisms are Ohmic mechanism and the space charge limited conduction mechanism.The transition voltage from Ohmic to Child's Law increases with the increase of concentration,and is directly proportional to the square of the film thickness.This indicates that the concentration of precursor solution affects the performance of the thin film through affecting the thickness.2?The effect of Zn doping on the properties of BFO films is great.Large remnant polarization?2P_r=129.6?C/cm²?at measured electric field value of 1000 kV/cm were obtained from the BFZO films doped with 2 mol%Zn.Zn doping can significantly reduce the leakage current of the film in the low electric field.The leakage mechanism analysis shows that the leakage mechanism of BFO thin film is mainly ohmic conduction in low electric field and F-N tunneling effect in high electric field.The change of leakage mechanism is related to the rupture of defective electron pair under high electric field.3?The doping of low-valence element on B-site has great influence on the performance of BFO film.We select Cu,Zn,Mn as the B-site low-valence doping elements,doping amount is 2 mol%.The results show that the substitution of Cu and Zn increase the remnant polarization of BFO thin films.The values of remnant polarization?2P_r?were 120.6 and126.7?C/cm² at 933kV/cm for Cu-doped and Zn-doped BFO thin film,respectively.Both Cu and Mn doping can reduce the leakage current of BFO films in the whole electric field,while Zn doping can reduce the leakage current of BFO film under low electric field.