Research On Preparation And Properties Of Sodium Bismuth Titanate Ferroelectric Thin Films

Ferroelectric thin films,as one of the most functional materials,are widely used in different kinds of electronic devices.As a new type of lead-free ferroelectric material,bismuth sodium titanate(Bi_0.5Na_0.5TiO₃,BNT)is considered to be one of the most promising ferroelectric films because of its excellent performance and low threat to environment.But the quality and properties of films are closely linked to processing methods,ink-jet printing technology,as one of the three dimensional printing technology,is expected to become an effective and convenient alternative for preparing films due to high flexibility and applicability?low cost and computer control.In this work,high performance BNT films were prepared by ink jet printing for the first time,proposing a new atmosphere for annealing of ferroelectric materials.We also studied the effect of different BiFeO₃ doping content on the properties of BNT films,and compared the properties of BNT-based films doped by different B-site ions on that condition.The main contents and results are listed as following:1.The BNT inks prepared via sol-gel method can be used to print by adjusting the viscosity and surface tension.The quality of films were greatly improved through the polycondensation of PEG,crack and pore free films were obtained due to the introduction of 70vol%PEG400 in precursor.The pure phase BNT films also can be synthesized on the condition of conventional annealing process by a heat treatment at650?for 30 minutes,the reason is attributed to two points,on one side,volatilization is suppressed through chelate rings between A-site ions and PEG,on the other side,oxide substrates assist in lowering the temperature for nucleation.2.Wet air was applied to anneal ferroelectric films considering the method of elimination for oxygen vacancies in perovskite proton conductor,the results of XPS and logI-logV characteristics confirmed the effectiveness of the reduction for oxygen vacancies.The mechanism of elimination was also discussed deeply,oxygen vacancies were hydrolyzed under humid atmosphere and created charged hydroxyl groups,which had less effect on the conductivity of ferroelectric films,therefore wet air was an effective alternative to improve properties of ferroelectric films.3.The BNT films were further studied by doping based on spinning coating,BiFeO₃-doped BNT films showed improved properties,depressing the deterioration of oxygen vacancies to ferroelectric properties through the defect complexes formed by Fe²⁺and oxygen vacancies.The result of BiCoO₃ doping was similar with BiFeO₃except BiAlO₃,whose solid solubility limit was lower than BiFeO₃ and BiCoO₃.Besides,the ink jet printing was better than spinning coating in terms of quality of depositing films.