| The thesis studies on the deposition and characterization ofxBInO3-(1-x)PbTiO3(xBI-(1-x)PT)thin films,including crystal structures,morphology,ferroelectricities,Curie temperature and piezoelectricities of the thin films.The full text is divided into five chapters,in addition to Chapter ? and Chapter ?,i.e.,introduction and conclusion respectively,the contents mainly include three parts:in the second chaper,xBI-(1-x)PT thin films prepared on MgO substrates and buffer layers,and study on the crystal structures,morphology,ferroelectricities,Curie temperature of the films;in the third chapter,preparation of cantilevers with xBI-(1-x)PT thin-films deposited on buffers and MgO substrates and study on the transverse piezoelectric properties of the films;and the fourth chapter,theoretical analysis of transverse piezoelectric properties of xBI-(1-x)PT thin films.The main contents are described briefly as follows:1.Preparation of xBI-(1-x)PT thin films and study on the crystal structures,ferroelectric,Curie temperature of thin filmsIn recent years,ferroelectric thin films have received extensive attention and research due to their applications in the fields of memory,surface acoustic wave and optoelectronic devices.In order to fabricate ferroelectric devices with high performances,the ferroelectric materials should have large remnant polarization(Pr)and high Curie temperature(Tc).Recently,a great attention has been paid to ferroelectric materials with perovskite structures because of high electrical performances and good temperature stability,which are required for applications in automotive and aerospace industries.It is important to develop new ferroelectric materials that have optimized electric properties and high Tc simultaneously.Recently,perovskite-type Bi(Me)O3-PbTiO3(Me:Sc,In,Y,Yb,etc.)solid solution systems as high temperature ferroelectric ceramics have become one of hot research topics.On the other hand,to achieve the miniaturization and high performance of electronic devices,researches were focused on developing new thin film materials.In chapter ?,for fabricating the xBI-(1-x)PT thin films with high ferroelectricities and high Curie temperature simultaneously,xBI-(1-x)PT thin films on(100)MgO crystal substrates are deposited using RF-magnetron sputtering method.The effects of different ratios of BiInO3 component and La doping of the films on high ferroelectricities and high Curie temperature are studied.In addition,the ferroelectric transition behaviors of the films are investigated by using Curie-Weiss law.At the end of this chapter,the xBI-(1-x)PT thin films deposited on Si substrate has been prepared,and the ferroelectricity of the films are tested preliminaryly.2.Experimental study on transverse piezoelectric properties of xBI-(1-x)PT thin films based on cantilever methodIt is well known that ferroelectric materials should have piezoelectric properties.Meanwhile,piezoelectric thin films have received increased attention in recent decades for their widely applications in ultrasonic electronic devices and MEMS,such as ultrasonic transducers,sensors,accelerometers,micro-pumps and energy harvesters,etc.To improve the properties of piezoelectric films,various piezoelectric perovskite crystals,solid solutions doped/mixed with different elements or compounds were studied and explored.In the multi-nary piezoelectric perovskites,several new materials were reported recently,such as Bi(Me)O3-PbTiO3(Me:Sc,In,Y,Yb,etc.)compounds,etc.The third chapter focuses on the transverse piezoelectric properties of La doping xBI-(1-x)PT thin films.The effective transverse piezoelectricities of xBI-(1-x)PT films are studied experimentally by multilayer cantilevers.Under the applied sinusoidal voltage,the tip vibration amplitudes of the xBI-(1-x)PT multilayer cantilevers are measured experimentally by laser Doppler vibrometer,and the effective transverse piezoelectric coefficients of the films with different x and La doping can be evaluated according to the theory of euler-bernoulli cantilever and piezoelectric equations.It is shown that,for 3 mol.%La-doped 0.15BI-0.85PT films,the optimized piezoelectric properties(e31,f=-9.35 C/m2)are obtained.Therefore,the optimized properties of the films can be obtained by properly controlling La doping contents.3.Theoretical analysis on transverse piezoelectric properties of xBI-(1-x)PT thin filmsBased on the experimental results of the piezoelectric characteristics in the third chapter,the transverse piezoelectric characteristics of La-doped BI-PT piezoelectric films are calculated and analyzed in the fourth chapter.It is obviousely,that the transverse piezoelectric characteristics of thin-film piezoelectric materials are related closely to the elastic parameters of the materials.But the elastic parameters of new materials,especially which is doped and modified,are always unknown.Generally,The elastic parameters can be calculated by using the first-principles method in the CASTEP(Cambridge Sequential Total Energy Package)module of Material Studio software.Then,the transverse piezoelectric properties of thin-film materials are calculated by finite element analysis using COMSOL software.In the fourth chapter,firstly,as example,the material parameters of PbTiO3 thin film are calculated by Material Studio software,then the La doped 0.15BI-0.85PT thin film materials are studied.Secondly,the transverse piezoelectric properties of the PZT-5A films are simulated by COMSOL software.Compared with published literature data of PZT films,the calculated effective transverse piezoelectric coefficient is reliable.At last,based on the method,the transverse piezoelectric properties of La-doped 0.15BI-0.85PT thin films prepared by this work are studied.By comparison,both results of the theory and experiment are in agreement with each other,which illustrate the theoretical calculations are available.Finally,in Chapter V,the conclusions and prospects are presented. |
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