铁电材料动态电—力学特性的相场数值研究

发布时间：2018-01-29 00:08

本文关键词： 铁电材料相场模型尺寸效应频率效应介电常数　出处：《北京理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：伴随着现代电子信息工业的飞速发展,铁电材料在电子、精密控制等领域得到了广泛的应用,经常被用于制作电容器、传感器和精密驱动器等元器件。微电子机械设备的小型化与集成化趋势要求铁电材料的尺寸越来越小,同时得益于纳米制备工艺的进步,材料内的晶粒尺寸随之不断降低。然而,随着晶粒尺寸的降低,铁电材料的特性会发生明显变化;此外,微电子机械设备通常在非静态的外场环境下工作,导致铁电材料处在动态的外场作用下,而不同的动态外场频率也会对铁电材料的特性造成影响。因此,为了保证元器件良好的工作性能,准确地探讨铁电材料电力学特性的外场频率效应、晶粒尺寸效应及其相关机理具有非常重要的意义。本文采用相场方法系统地研究了纳米钛酸钡陶瓷电力学特性的外场频率效应和晶粒尺寸效应,构造了包含晶界的二维多晶相场模型,并利用与时间相关的金兹堡-朗道动力学方程控制极化向量的演变。为了获得标准的电滞回线,我们对多晶模型施加了较大幅值的正弦电场让极化能够发生翻转,进而研究了钛酸钡陶瓷的铁电性、介电性与压电性。但是,实验测量铁电材料的介电常数一般是对其施加小信号电压。因此,本文也采用对模型施加小幅值电场的方法来计算材料介电常数。本文中,假设铁电陶瓷的频率响应来自于外场加载速度与材料微结构演化速度相互竞争的结果。基于这一假设我们采用相场方法系统地对不同外场加载频率下材料的微结构演化进行了数值模拟计算。首先我们研究了大幅值电场作用下晶粒尺寸为100nm的钛酸钡陶瓷特性随电场频率(10 Hz到2500Hz)的变化规律,发现矫顽场随频率的增加而增加,切线介电常数和切线压电常数随频率的增加而减小。我们也发现在低频时,晶体内部极化可以发生180°翻转,但在较高的频率下,极化只会发生90°翻转。其次我们还发现小幅值电场作用下晶粒尺寸为100 nm钛酸钡陶瓷的介电常数随电场频率的增加而降低。最后我们研究了动力学参数对计算结果的影响,发现动力学参数和外加电场频率的取值大小在对钛酸钡陶瓷特性的影响上是呈相反趋势。在研究钛酸钡纳米陶瓷特性的晶粒尺寸效应时,我们发现如果不考虑晶界的影响,计算结果便不能体现尺寸效应,这说明晶界的存在是铁电陶瓷呈现尺寸效应的重要原因之一。对此,本文通过对晶粒尺寸为10 nm到170 nm的钛酸钡陶瓷施加频率为100Hz的大幅值电场,得到了电滞回线和蝶形曲线随晶粒尺寸的变化规律;探讨了剩余极化、矫顽场、切线介电常数切线压电常数以及小幅值电场作用下的介电常数随晶粒尺寸的变化规律。分析表明,晶界的“稀释”效应以及晶界对畴结构的影响均是影响钛酸钡纳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 掳. 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.
【学位授予单位】：北京理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB34

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