Study On The Cation Position Regulation And Properties Of Single Phase Bi/Ga Based Multiferroic Films

Multiferroic material is a typical advanced functional material due to the simultaneous existence of ferroelectric,ferromagnetic and ferroelastic sequences,it contains a very rich multifield coupling effect,such as piezoelectric,piezomagnetic and magnetoelectric coupling effects.Nanostructures have rich surface interface effects and size effects,and have many excellent properties that are different from bulk materials.Therefore,multiferroic nanomaterials can enable devices to be multifunctional,integrated,and miniaturized,which brings microelectronics and information technology a revolutionary development.Multiferroic materials have broad application prospects in sensors,drivers,converters,attenuators,filters,field probes,memory,and microelectronics industries.Because of these remarkable characteristics,multiferroic materials are also an important research direction in the fields of materials,physics,and solid mechanics,and contain rich materials science,physics,and mechanics issues,which have attracted the attention of scientists around the world.In this thesis,for the first time,the 0.86BiTi_0.1Fe_0.8Mg_0.1O₃-0.14CaTiO₃（BTFM-CTO）multiferroic single crystal epitaxial thin film was prepared by sol-gel method;and the cation site components were adjusted for（1-x）BiTi_（1-y）/2Fe_yMg_（1-y）/2O₃-（x） CaTiO₃,x=0.14,0.18,0.22,0.26,0.30,y=0.8.The study shows that when x=0.22 component,the piezoelectric response of BTFM-CTO film is relatively the largest.At the same time,the new multiferroic material Ga Fe O₃（GFO）is doped.We systematically explores the electrical and magnetic properties of two kinds multiferroic films.The research content of this paper includes the following three aspects:（1）For the first time,the 0.86BiTi_0.1Fe_0.8Mg_0.1O₃-0.14CaTiO₃ multiferroic single crystal epitaxial thin film was grown on a niobium-doped strontium titanate substrate（Nb STO）by sol-gel method.Reciprocal space（RSM）analysis shows that the film has a single crystal epitaxial structure,which shows excellent piezoelectric properties and weak ferromagnetism,and the magnetoelectric coupling performance is improved significantly compared to the undoped Bi Fe O₃ film material.（2）Due to the large influence of lattice strain on the ferroelectric properties of thin-film materials,it is necessary to adjust the cation site of（1-x）BiTi_（1-y）/2Fe_yMg_（1-y）/2O₃-（x）CaTiO₃ to determine the optimal piezoelectric performance of the material system.The study shows BTFM-CTO material has the relatively largest piezoelectric response at component of x=0.22,which close to the morphotropic phase boundary.STEM result shows that the film with x=0.22 component still exhibits good epitaxial properties,but the polarization direction is change obviously,which is probably owing to the coexistence of tetragonal phase and cubic phase.（3）Based on the sol-gel method combined with spin coating process,the cation position of the GaFeO₃ film is adjusted.The ferroelectric properties of the doped Ga_0.97Zn_0.03Fe_0.97Ti_0.03O₃ film has not been improved greatly compared to that of GFO film due to the poor quality of the film,and the loose structure of film results in large leakage current,which makes it difficult to test the macroscopic and microscopic ferroelectric performance.