本文關鍵詞： 鐵電材料 相場模型 尺寸效應 頻率效應 介電常數(shù)　出處：《北京理工大學》2015年碩士論文　論文類型：學位論文

【摘要】：伴隨著現(xiàn)代電子信息工業(yè)的飛速發(fā)展,鐵電材料在電子、精密控制等領域得到了廣泛的應用,經常被用于制作電容器、傳感器和精密驅動器等元器件。微電子機械設備的小型化與集成化趨勢要求鐵電材料的尺寸越來越小,同時得益于納米制備工藝的進步,材料內的晶粒尺寸隨之不斷降低。然而,隨著晶粒尺寸的降低,鐵電材料的特性會發(fā)生明顯變化;此外,微電子機械設備通常在非靜態(tài)的外場環(huán)境下工作,導致鐵電材料處在動態(tài)的外場作用下,而不同的動態(tài)外場頻率也會對鐵電材料的特性造成影響。因此,為了保證元器件良好的工作性能,準確地探討鐵電材料電力學特性的外場頻率效應、晶粒尺寸效應及其相關機理具有非常重要的意義。本文采用相場方法系統(tǒng)地研究了納米鈦酸鋇陶瓷電力學特性的外場頻率效應和晶粒尺寸效應,構造了包含晶界的二維多晶相場模型,并利用與時間相關的金茲堡-朗道動力學方程控制極化向量的演變。為了獲得標準的電滯回線,我們對多晶模型施加了較大幅值的正弦電場讓極化能夠發(fā)生翻轉,進而研究了鈦酸鋇陶瓷的鐵電性、介電性與壓電性。但是,實驗測量鐵電材料的介電常數(shù)一般是對其施加小信號電壓。因此,本文也采用對模型施加小幅值電場的方法來計算材料介電常數(shù)。本文中,假設鐵電陶瓷的頻率響應來自于外場加載速度與材料微結構演化速度相互競爭的結果�；谶@一假設我們采用相場方法系統(tǒng)地對不同外場加載頻率下材料的微結構演化進行了數(shù)值模擬計算。首先我們研究了大幅值電場作用下晶粒尺寸為100nm的鈦酸鋇陶瓷特性隨電場頻率(10 Hz到2500Hz)的變化規(guī)律,發(fā)現(xiàn)矯頑場隨頻率的增加而增加,切線介電常數(shù)和切線壓電常數(shù)隨頻率的增加而減小。我們也發(fā)現(xiàn)在低頻時,晶體內部極化可以發(fā)生180°翻轉,但在較高的頻率下,極化只會發(fā)生90°翻轉。其次我們還發(fā)現(xiàn)小幅值電場作用下晶粒尺寸為100 nm鈦酸鋇陶瓷的介電常數(shù)隨電場頻率的增加而降低。最后我們研究了動力學參數(shù)對計算結果的影響,發(fā)現(xiàn)動力學參數(shù)和外加電場頻率的取值大小在對鈦酸鋇陶瓷特性的影響上是呈相反趨勢。在研究鈦酸鋇納米陶瓷特性的晶粒尺寸效應時,我們發(fā)現(xiàn)如果不考慮晶界的影響,計算結果便不能體現(xiàn)尺寸效應,這說明晶界的存在是鐵電陶瓷呈現(xiàn)尺寸效應的重要原因之一。對此,本文通過對晶粒尺寸為10 nm到170 nm的鈦酸鋇陶瓷施加頻率為100Hz的大幅值電場,得到了電滯回線和蝶形曲線隨晶粒尺寸的變化規(guī)律;探討了剩余極化、矯頑場、切線介電常數(shù)切線壓電常數(shù)以及小幅值電場作用下的介電常數(shù)隨晶粒尺寸的變化規(guī)律。分析表明,晶界的“稀釋”效應以及晶界對疇結構的影響均是影響鈦酸鋇納米陶瓷特性的重要因素。
[Abstract]:With the rapid development of modern electronic information industry, ferroelectric materials have been widely used in electronics, precision control and other fields, often used to make capacitors. The miniaturization and integration of microelectromechanical devices require the size of ferroelectric materials to be smaller and smaller, while the progress of nano-fabrication technology is beneficial. However, with the decrease of grain size, the properties of ferroelectric materials will change obviously. In addition, the microelectromechanical equipment usually works in the non-static external field environment, which results in the ferroelectric material in the dynamic external field, and different dynamic external field frequency will also affect the characteristics of the ferroelectric material. In order to ensure the good performance of components, the external frequency effect of ferroelectric material's electric characteristics is discussed accurately. Grain size effect and its related mechanism are of great significance. In this paper, the external field frequency effect and grain size effect of electrical properties of nanometer barium titanate ceramics are systematically studied by phase field method. A two-dimensional polycrystalline phase field model including grain boundaries is constructed, and the evolution of polarization vector is controlled by using the time-dependent Kinzbau-Landau dynamic equation to obtain the standard hysteresis loop. We applied a large sinusoidal electric field to the polycrystalline model to make the polarization flip, and then studied the ferroelectric, dielectric and piezoelectric properties of barium titanate ceramics. The dielectric constant of ferroelectric material is generally measured by applying small signal voltage. Therefore, the method of applying a small electric field to the model is also used to calculate the dielectric constant of ferroelectric material in this paper. The frequency response of ferroelectric ceramics is assumed to be the result of competition between external field loading velocity and material microstructure evolution velocity. Based on this assumption, we systematically apply phase field method to microjunction of materials at different external field loading frequencies. The structure evolution of barium titanate ceramics with 100 nm grain size under the action of large electric field has been numerically simulated and calculated. From 10Hz to 2500Hz). It is found that the coercive field increases with the increase of frequency, and the dielectric constant and piezoelectric constant of tangent decrease with the increase of frequency. But at higher frequencies. The polarization will only turn over 90 擄. Secondly, we also find that the grain size is 100 under the action of a small electric field. The dielectric constant of nm barium titanate ceramics decreases with the increase of electric field frequency. Finally, the influence of kinetic parameters on the calculated results is studied. It is found that the effect of kinetic parameters and the frequency of applied electric field on the properties of barium titanate ceramics is opposite, and the effect of grain size on the properties of barium titanate nanocrystalline ceramics is studied. We find that the size effect can not be reflected in the calculation results if the effect of grain boundary is not considered, which indicates that the existence of grain boundary is one of the important reasons for the size effect of ferroelectric ceramics. In this paper, by applying a large electric field of 100Hz to the barium titanate ceramics with grain size from 10 nm to 170 nm, the changes of hysteresis loop and butterfly curve with grain size are obtained. The variation of residual polarization, coercive field, tangent dielectric constant and dielectric constant with small electric field with grain size is discussed. The "dilution" effect of grain boundary and the effect of grain boundary on domain structure are important factors affecting the properties of barium titanate nanocrystalline ceramics.
【學位授予單位】：北京理工大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TB34

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相關期刊論文 前1條

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本文編號：1471941