锰掺杂诱导层状类钙钛矿结构薄膜取向生长及铁电性能OA

Introduction The Aurivillius type layered perovskite structure compound can be represented by a chemical formula(Bi2O2)2+(An-1BnO3n+1)2-.Its crystal structure can be seen as a unique"natural superlattice"structure composed of alternating layers of perovskite-like structure and fluorite-like structure along the c-axis direction.Among them,n represents the number of layers of BO6 octahedra in the c-axis direction in the perovskite structure layer(i.e.,n=1,2,3,4,5,...).The value of n determines the thickness of the perovskite layer and physical properties of the material.The A-site ion is located at the octahedral apex of the perovskite like layer,with 12 coordination.Usually,it can be larger cations such as Ba2+,Sr2+,Ca2+,Pb2+,K1+,Na1+,Bi3+,and Ln3+(lanthanide elements).Multiple ion substitutions can be achieved to regulate the performance.The B-site ion is located at the center of the oxygen octahedron and coordinated with 6.Usually,it can be small high valence transition metal ions such as Fe3+,Ti4+,Nb5+,Ta5+,W6+,and Mo6+).The displacement of B-site ions is one of the main sources of ferroelectric polarization.The stereochemical activity of the 6s2 lone pair electrons of Bi3+ions also has a significant impact on their structure and polarization.From the chemical formula and crystal structure above,it can be inferred that this type of compound can have a broad spectrum of physical and chemical properties as well as tunability,while the physical and chemical properties can be accompanied by significant anisotropic characteristics. Methods Acetate and tetrabutyl titanate[Ti(OC4H9)4]were used as starting materials solvent in acidic solutions.A 10%excess amount of Bi(CH3COO)3 was used to compensate the Bi volatilization in the process.Before spin coating,the substrates were cleaned ultrasonically in acetone,alcohol and deionized water,sequently.The spin coating and baking processing were repeated to enhance the thickness.Finally,the baked thin films were crystallized in ambient atmosphere at 700℃for 10 min by rapid thermal annealing. The crystal structure for the derived thin films was determined by X-ray diffraction(XRD,Philips Co.,the Netherlands)with Cu kα radiation.The thickness and the surface morphologies were characterized by field-emission scanning electron microscopy(FE-SEM,FEI Co.,Japan).Au electrodes of 0.2 mm in diameter were deposited by a sputter(China)onto the surfaces of thin films through a shadow mask.The ferroelectric and leakage properties were measured by a standard ferroelectric test system(Radiant Technologies Co.,USA). Results and discussion For the sample with x of 0,its main diffraction peaks correspond one-to-one with the six-layered perovskite structure,which can be classified as the A21am space group,belonging to a typical even layered Aurivillius type compound.There are no diffraction peaks of other impurities except for the substrate diffraction peak.After introducing element Mn doping,the doped film still maintains the layered structure characteristic peak position as a whole,and there is no significant shift.In general,doping often leads to a shift in diffraction peak position due to the difference in ionic radius,which is usually one of the reference evidences for doping elements entering the main lattice.There is no significant shift in the diffraction peak position of the Mn ion doped film possibly due to the unsuccessful entry of Mn ions into the main lattice or the fact that the radius of Mn ion(0.064 5 nm)is the same as the radius of Fe ion(0.064 5 nm).As x increases,the most intense diffraction peak of the sample gradually shifts from(1113)to(0014),and the(00l)series diffraction peaks gradually increase in intensity,indicating that the c-axis orientation of the thin film is strengthened.This change is not significant in ceramic samples,but it is also evident.The change in relative peak intensity also confirms the doping of Mn ions into the main lattice,indicating that the diffraction peak position is not significantly shifted due to the same ion radius.For the structural characteristics of Aurivillius type compounds,especially their polarization anisotropy,this preferred orientation can inevitably have a profound impact on the electrical properties of thin films. Conclusions The BFTM thin films doped with manganese ions were prepared by a chemical solution method.The preferred orientation of the film's c-axis enhanced,and the orientation factor increased from 0.08 as x=0 to 0.89 as x=1.00 with the increase of manganese ion doping content.The ferroelectric properties of the thin film were enhanced with doping,and the effective residual polarization reached its maximum as x=0.50.This work could provide an experimental reference for the preparation and ferroelectric properties of Aurivillius type layered perovskite structure thin films.These results could indicate the anisotropic characteristics of the crystal structure polarization of this type of compound,and provide feasible strategies for the preparation of preferred orientation thin films and performance control.