發(fā)布時間：2018-08-07 21:42

【摘要】：獨特的微觀疇結構使得鐵電材料具有優(yōu)越的物理特性和廣泛的應用前景,吸引著眾多科研工作者的關注。壓電力顯微鏡(PFM)作為在納米尺度表征鐵電材料的重要工具,被廣泛地用于鐵電疇的研究中。但電疇自身的非均勻性、PFM導電探針激發(fā)的電場高度局域性、以及探針與測試材料間復雜的長程力電相互作用,使得PFM測試定量分析還存在著很大困難,這嚴重阻礙了鐵電材料納米尺度力電耦合的研究,延緩了基于納米尺度力電耦合性能電子元器件的開發(fā)。為此,本論文針對PFM技術,定量分析了鐵電疇結構,包括電疇尺寸、疇壁及其厚度等因素,對鐵電材料納米尺度壓電變形的影響,相應的研究內(nèi)容和成果概括如下:第一,建立起了復雜鐵電疇結構納米尺度壓電變形的理論框架。通過鏡像電荷方法,計算模擬出了導電探針所激發(fā)的電場;考慮到復雜鐵電多疇結構的極化取向及空間壓電張量的非均勻分布,結合彈性本構方程,通過格林函數(shù)方法,推導出了復雜鐵電疇結構納米尺度壓電位移分析的基本理論框架,為分析電疇尺寸和疇壁對納米尺度壓電變形的影響提供了基本理論框架。第二,計算分析了鐵電疇壁處納米尺度壓電響應,揭示出了其特殊納米尺度壓電變形的機理。通過模擬分析發(fā)現(xiàn)面外非電荷疇會出現(xiàn)特殊的面內(nèi)壓電響應,而面內(nèi)電荷疇則會出現(xiàn)特殊的面外壓電響應,究其原因在于:面外非電荷疇壁處的面內(nèi)壓電位移來源于長程力電約束反對性的破壞,而面內(nèi)電荷疇壁處的面外位移響應則源于面內(nèi)壓電位移的不連續(xù)。第三,分析了疇壁厚度對鐵電疇納米尺度壓電變形的影響,提出了增加疇壁厚度增強納米尺度力電耦合性能的方案。通過將疇壁視為具有一定厚度的均勻的壓電介質(zhì),且其壓電系數(shù)取決于其厚度和相鄰電疇的壓電系數(shù),并基于此,分析并發(fā)現(xiàn)增大疇壁厚度能夠增強90非度電荷的橫向壓電響應和90電荷疇的垂直壓電響應,提出了基于增加疇壁厚度提高鐵電材料納米尺度力電耦合性能的新方法。第四,計算分析了電疇尺寸、傾斜疇壁及疇壁厚度對周期性鐵電疇納米尺度壓電變形的影響。通過對周期性鐵電疇結構的計算分析,發(fā)現(xiàn)疇壁的傾斜打破了鐵電疇的納米尺度壓電位移響應的對稱性,但并沒有改變其變形起伏的周期性,且合適的電疇尺寸,才能使得周期性鐵電材料同時具有優(yōu)異的力電性能和較小的性能起伏。本論文的研究工作和研究成果,實現(xiàn)了復雜鐵電疇納米尺度壓電變形的定量分析,為PFM技術的應用和發(fā)展提供了良好的理論基礎和指導,也為制備優(yōu)異納米尺度壓電性能的鐵電材料提供了一定的實驗方案。
[Abstract]:Because of its unique microcosmic domain structure, ferroelectric materials have excellent physical properties and wide application prospects, which have attracted the attention of many researchers. As an important tool to characterize ferroelectric materials at nanometer scale, (PFM) has been widely used in ferroelectric domain research. However, the heterogeneity of domain itself and the high localization of electric field excited by PFM conductive probe, as well as the complex long range electric interaction between the probe and the test material, make the quantitative analysis of PFM measurement difficult. This seriously hinders the research of nano-scale electromechanical coupling of ferroelectric materials, and delays the development of electronic components based on nano-scale electromechanical coupling. Therefore, aiming at PFM technology, this paper quantitatively analyzes the effect of ferroelectric domain structure, including domain size, domain wall and its thickness, on ferroelectric nanoscale piezoelectric deformation. The corresponding research contents and results are summarized as follows: first, A theoretical framework for nanoscale piezoelectric deformation of complex ferroelectric domain structures is established. The electric field excited by the conductive probe is simulated by the mirror charge method, considering the polarization orientation of the complex ferroelectric multi-domain structure and the non-uniform distribution of the space piezoelectric Zhang Liang, and combining with the elastic constitutive equation, the Green's function method is used. The basic theoretical framework of nano-scale piezoelectric displacement analysis for complex ferroelectric domain structures is derived, which provides a theoretical framework for analyzing the effects of domain size and domain wall on nano-scale piezoelectric deformation. Secondly, the nanoscale piezoelectric response at the ferroelectric domain wall is calculated and analyzed, and the mechanism of its special nanoscale piezoelectric deformation is revealed. Through simulation analysis, it is found that there is a special in-plane piezoelectric response in the off-plane uncharged domain and a special out-of-plane piezoelectric response in the in-plane charge domain. The reason lies in that the in-plane piezoelectric displacement at the off-plane uncharged domain wall originates from the failure of the long-course electrically constrained opposition, while the out-of-plane displacement response at the in-plane charge domain wall is due to the discontinuity of the in-plane piezoelectric displacement. Thirdly, the effect of domain wall thickness on ferroelectric domain nanoscale piezoelectric deformation is analyzed. The domain wall is regarded as a uniform piezoelectric dielectric with a certain thickness, and its piezoelectric coefficient depends on its thickness and the piezoelectric coefficient of adjacent domains. It is found that the transverse piezoelectric response of 90 degree charge and the vertical piezoelectric response of 90 charge domain can be enhanced by increasing the thickness of domain wall. A new method is proposed to improve the mechanical and electrical coupling performance of ferroelectric materials at nanometer scale based on the increase of domain wall thickness. Fourthly, the effects of domain size, inclined domain wall and the thickness of domain wall on the nanoscale piezoelectric deformation of periodic ferroelectric domains are calculated and analyzed. Through the calculation and analysis of the periodic ferroelectric domain structure, it is found that the inclination of domain wall breaks the symmetry of the nanoscale piezoelectric displacement response of the ferroelectric domain, but does not change the periodicity of its deformation and fluctuation, and the appropriate electric domain size. In order to make periodic ferroelectric materials at the same time have excellent mechanical and electrical properties and small performance fluctuations. In this paper, the quantitative analysis of complex ferroelectric domain nanoscale piezoelectric deformation is realized, which provides a good theoretical basis and guidance for the application and development of PFM technology. It also provides a certain experimental scheme for the preparation of ferroelectric materials with excellent nano-scale piezoelectric properties.
【學位授予單位】：湘潭大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TB383.1

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本文編號：2171438