## 物理代写|固体物理代写Solid-state physics代考|KYA322

2023年3月29日

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## 物理代写|固体物理代写Solid-state physics代考|Comparison Between Bonds of Various Kinds

The ionic bond involves electron transfer and is non-directional. The covalent bond involves electron sharing and is directional. The third type of bond, that is, metallic bond involves electron sharing and is non-directional. In this case the valence electrons are said to be delocalized electrons; that is they have an equal probability of being associated with any of a large number of adjacent atoms.

The van der Waals bond is the most universal one. It exists in all the cases. This is the weakest having an energy of the order of $10^4 \mathrm{~J} / \mathrm{mol}$. Ideally, it operates between neutral atoms, or molecules with closed inner electron shell. These forces are responsible for the existence of liquid and solid state of inert gases, hydrogen, oxygen, nitrogen and many other organic and inorganic compounds. Because of low energy values of the van der Waals bond all structure based on it are unstable, volatile and have low melting temperatures.

The energy of ionic bond is much higher than that of the van der Waals bond and may be as high as $10^6 \mathrm{~J} / \mathrm{mol}$. Therefore, solid based on the ionic bond has high melting temperature. The ionic bond is very frequent among inorganic compounds such as metal halides, metallic oxides, sulphides and other polar compounds.

The covalent bond is very frequent among organic compounds but it also present in inorganic compounds, in some metals and in numerous intermetallic compounds. The energy of the covalent bond is also high $\left(10^6 \mathrm{~J} / \mathrm{mol}\right)$ resulting in high melting temperature of the solids. This bond is responsible for the existence of diamond, Ge, Si etc.

The metallic bond is characteristic of typical metals and various intermetallic compounds. The order of the magnitude of the energy of this type of bond is comparable to that of energy of covalent bond. The hydrogen bond is relatively weak and plays an important part.

## 物理代写|固体物理代写Solid-state physics代考|Classification of Defects

In an ideal crystal structure every unit cell is identical and each has a specified shape, size and cell contents. The concept of an ideal crystal with a perfect arrangement of atoms is valid only at $0 \mathrm{~K}$, and then there is no entropy contribution. However, at a finite temperature, a certain disorder is introduced into the structure of solids and solid becomes structurally imperfect. Some cells may have one or more atoms less whereas others may have more atoms than the ideal unit cell. The imperfections of the crystal are called crystal defects.

Imperfection in crystals may be classified on the basis of their geometry such as point, line and surface imperfection. Point defects are zero dimensional dimension defects confined over a few interatomic distances other defects such as line defects and surface defect extend through microscopic region in crystal.

Point defects (zero dimensional defects): The important point defects are:
(i) Vacancies: Whenever one or more atoms are missing from a normally occupied position, as shown in Fig. 3.1, the defect caused is known as vacancy.
(ii) Interstitial defects: Whenever an extra atom (generally smaller than the parent atoms) occupies interstitial position in the crystal system without dislodging the parent atom as shown in Fig. 3.2, the defect caused is known as interstitial defect
(iii) Substitutional defect: Whenever an impurity atom (other than the parent atoms) occupies a position which was initially meant for a parent atom, as shown in Fig. 3.3, the defect caused is known as substitutional defect.
(iv) Frankel defect: It consists of an atom displaced from its regular site to an interstitial site. The atom in the interstitial site and the vacancy caused by the

(v) Schottky defect: In ionic crystals if there is a vacancy in positive ion site, then charge neutrality of crystal can be maintained by creating a vacancy in the neighbouring negative ion site (Fig. 3.5), such a pair of vacant site is called Schottky defect.

# 固体物理代写

## 物理代写|固体物理代写Solid-state physics代考|Classification of Defects

(i) 空位：每当一个或多个原子从正常占据的位置丢失时，如图 3.1 所示，引起的缺陷称为空位。
(ii) 间隙缺陷：每当一个额外的原子（通常小于母原子）占据晶体系统的间隙位置而没有移动母原子，如图 3.2 所示，引起的缺陷称为间隙缺陷 (iii) 置换

(iv) Frankel 缺陷：它由一个原子组成，该原子从其常规位点转移到间隙位点。间隙位点中的原子及其引起的空位

(v) 肖特基缺陷：在离子晶体中，如果正离子位置存在空位，则可以通过在相邻的负离子位置创建空位来保持晶体的电荷中性（图 3.5），这样一对空位是称为肖特基缺陷。

## 有限元方法代写

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## MATLAB代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。