材料物理性能1

1、Physics properties of material 1. Dielectric properties 2. Magnetic properties Long Yi 学习网：wu.wuxing. ; 密码：wuxing2010123学习方法：1。作业（40分）：每人做一次作业。但是每人作业不同：作业1。将其中一节译成中文，或者校正其中一节，便于同学学习。要求：在规定的时间以前传上网，上课用。专用名词翻译准确，文字通顺。公式要写出来。作业2。做一道习题，便于同学学习。要求：交纸质版。步骤清楚。如果没有在规定时间内传上网，或者交作业，重新再作新作业。每人的作业在网上 。42。考试(60分）

2、：开卷，6道题，2.5小时，不设考场和监考，成绩和交卷时间相关。考题和习题相似。3。分数可以考虑整体提高。去年：60-80：35，80-90：40，90-100：2857.1The relative permittivity( dielectric constant) r is defined to reflect a increase in the capacitance:意义: The increase in the stored charge is due to the polarization of the dielectric by the applied field.1。相对介电常

3、数定义: 62。The definition of electric dipole moment.意义: 73。Definition of Polarizabilitypinduced = induced dipole moment, = polarizability, E = electric field 极化率, pinduced = E8举例Electronic Polarizationpe = magnitude of the induced electronic dipole moment, Z = number of electrons orbiting the nucleus o

4、f the atom, x = distance between the nucleus and the center of negative charge, = constant, E = electric field9Static Electronic Polarizabilitye = electronic polarizabilityZ = total number of electrons around the nucleus me = mass of the electron in free spaceo = natural oscillation frequency注意的来源10

5、Examaple 1.711Electronic polarizability and its resonance frequency versus the number of electrons in theatom (Z). The dashed line is the best-fit line. 注意：f0在光频12(a) When a dilectric is placed in an electric field, bound polarization charges appear on the opposite surfaces. (b) The origin of these

6、polarization charges is the polarization of the molecules of the medium. (c) We can represent the whole dielectric in terms of its surface polarization charges +QP and -QP.4.材料的表面极化电荷密度和极化强度定义13Definition of Polarization VectorP = Polarization vector, p1, p2, ., pN are the dipole moments induced at

7、N molecules in the volumeDefinition of Polarization Vectorpav = the average dipole moment per moleculeP = polarization vector, N = number of molecules per unit volumeP = Npav14Polarization and Bound Surface Charge DensityP = polarization, p = polarization charge density on the surfaceP = p15Polariza

8、tion charge density on the surface of a polarized medium is related to the normalcomponent of the polarization vector.165。Definition of Electronic SusceptibilityP = eoEP = polarization, e = electric susceptibility, o = permittivity of free space, E = electric field17Electric Susceptibility and Polar

9、izatione = electric susceptibility, o = permittivity of free space, N = number of molecules per unit volume, e = electronic polarizabilityRelative Permittivity and Electronic Susceptibilityr = relative permittivity, e = electric susceptibilityr = 1 + e18Relative Permittivity and Polarizabilityr = re

10、lative permittivityN = number of molecules per unit volumee = electronic polarizabilityo = permittivity of free spaceAssumption: Only electronic polarization is present19The electric field inside a polarized dielectric at the atomic scale is not uniform. The local field is the actual field that acts

11、 on a molecules. It can be calculated by removing that molecules and evaluating the field at that point from the charges on the plates and the dipoles surrounding the point.20Local Field in DielectricsEloc = local field, E = electric field, o = permittivity of free space, P = polarizationClausius-Mo

12、ssotti Equationr = relative permittivity, N = number of molecules per unit volume, e = electronic polarizability, o = permittivity of free space21Example 7.222(a) Valence electrons in covalent bonds in the absence of an applied field. (b) When an electric field is applied to a covalent solid, the va

13、lence electrons in the covalent bonds are shifted very easily with respect to the positive ionic cores. The whole solid becomes polarized due to the collective shift in the negative charge distribution of the valence electrons.6.共价键晶体中电子极化232425A NaCl chain in the NaCl crystal without an applied fie

14、ld. Average or net dipole moment per ion is zero. In the presence of an applied field the ions become slightly displaced which leads to a net average dipole moment per ion.7.3.1离子极化7.3 polarization mechanisms26Ionic Electric Orinetational Polarization PavEloc27(a) A HCl molecule possesses a permanen

15、t dipole moment p0.(b) In the absence of a field, thermal agitation of the molecules results in zero net averagedipole moment per molecule.(c) A dipole such as HCl placed in a field experiences a torque that tries to rotate it to align p0with the field E.(d) In the presence of an applied field, the

16、dipoles try to rotate to align with the field against thermal agitation. There is now a net average dipole moment per molecule along the field.7.3.2。偶极子极化28Average Dipole Moment in Orientational Polarizationpav = average dipole moment, po = permanent dipole moment, E = electric field, k = Boltzmann

17、constant, T = temperatureDipolar Orientational Polarizabilityd = dipolar orientational polarizability, po = permanent dipole moment29(a) A crystal with equal number of mobile positive ions and fixed negative ions. In the absence of a field, there is no net separation between all the positive charges

18、 and all the negative charges.(b) In the presence of an applied field, the mobile positive ions migrate toward the negativecharges and positive charges in the dielectric. The dielectric therefore exhibits interfacialpolarization.(c) Grain boundaries and interfaces between different materials frequently give rise to Interfacial polarization.7.3.3。界面极化307.3.4Total Induced Dipole Momentpav = e Eloc + i Eloc + d Elocpav = average dipole moment, Eloc = local electric field, e = electronic polarizability, i = ioni