材料物理（Material physics ）

1、材料物理2（Material physics 2）Fill in the. Noun interpretation1. phonon: energy quantum of independent harmonic oscillator in lattice vibration.Wave characteristics: the propagation medium is not connected with the medium. It is the crystal lattice of the yard, ion, etc. The lattice vibration mode (wave

2、is on the lattice thermal vibration of atoms can be described as similar to the mechanical results of wave propagation, the wave is called latticewave)Griffith crack theory: Griffith that many tiny cracks or defects exists in actual material, under the action of external force, and these cracks arou

3、nd the defect will produce stress concentration phenomenon, when the stress reaches a certain level, the crack began to rupture propagation. This is the famous theory of Griffith microcracks.The mechanism of particle reinforced material is that particles can prevent dislocation movement in the matri

4、x or absorb part of the energy through plastic deformation of particles, thus strengthening the purpose.The reason of thermal expansion hysteresis in complex is that the expansion coefficient varies greatly in different directions between different phases or grains, resulting in great internal stres

5、s, resulting in microcracks.There are several types of crack propagation: fracture type (the main cause of low stress fracture) (Zhang Kaihang, I type), stagger type (sliding type, II type), tearing type (III type)The nature of thermal breakdown: a medium in an electric field that is heated due to d

6、ielectric loss and may be charged from a heat balance state of heat dissipation and heating when the applied voltage is high enough. If the energy emitted is greater than that, the temperature of the medium will become higher and higher until permanent damage occurs.The carriers in conducting materi

7、als: any substance, as long as the existence of free particle charge, which can be produced in the electric field to store the current carrier metal conductor is the free electron, inorganic materials (electronic negative electron, ion (hole) ions or voids) as carrier ion conductance said as a carri

8、er for ionic conductance, the electron conductance called electronic conductivityThe form of force and deformation of inorganic materials; elastic deformation; plastic deformation; viscous flow; high temperature creepThe factors causing phonon scattering, phonon frequency and doping point defectsAt

9、the Curie point in dielectric polarization mechanism; electron polarization, ion displacement polarization and ionic relaxation polarization, spontaneous polarization (some dielectric at a certain temperature, when the external electric field after the withdrawal is still a certain polarization)The

10、main structure of ferrite in structure: the spinel garnet type 3 magnetoplumbite type 4 5 6 perovskite type ilmenite type tungsten bronze typeThe particle diffusion mechanism includes: sublattice gap diffusion; vacancy diffusion; interstitial diffusion mechanismDielectric breakdown type: thermal bre

11、akdown, electric breakdown, partial discharge breakdownFracture energy: the action of an external force on an object per unit volume until an object is broken by an external forceSurface discharge; surface discharge of solid medium belongs to gas discharge; solid medium is often in the surrounding g

12、as and coal; sometimes the medium itself does not break through, but sparks blow over its surface, which is surface discharge.The intrinsic conductivity and impurity conductivity; basic ion source in the crystal lattice of the movement known as the intrinsic conductance (intrinsic ion conductance) c

13、aused by the movement of the fixed ion is weak, is the main impurity ions, called impurity conductivity.Space charge polarization: under the action of electric field, the positive and negative interstitial ions in inhomogeneous media move towards negative and positive poles respectively. The change

14、in the density of the ions in the ceramic body results in an electric dipole moment, which is called space charge polarization.Equilibrium carriers and nonequilibrium carriers: at certain temperatures, carriers due to thermal excitation in semiconductors are called equilibrium carriers. Due to exter

15、nal conditions (plus voltage). Guang Zhao) a carrier with a large number of carriers is called a non-equilibrium carrierPressure sensitive effect refers to the effect of nonlinear resistor sensitive to voltage changes, which is in a critical voltage condition, the resistance value is very high, almo

16、st no current through, exceeds the critical voltage (voltage sensitive resistor) value decreased quickly, so that the current through the.Dielectric strength: when the electric field strength exceeds a critical value. The phenomenon that a dielectric changes from a dielectric state into a conductive

17、 state is called a breakdown in dielectric strength. The corresponding critical field strength is called dielectric strength.What is the essence of absorption of light by a medium?As an energy flow, light passes through the medium, causing the valence electron transition of the medium, or the atomic

18、 vibration, to consume energy. In addition, the valence electrons in the medium absorb the photon energy and excite it. Yet when a photon deexcitation, collisions with other molecules in motion, i.e. thermal energy transformation kinetic energy electrons into molecules, which constitute the light at

19、tenuation, even in the transparent medium is not light scattering of light, there will be loss of energy, light absorption.4., why do most ceramic materials do not produce plastic deformation at normal temperature, but brittle fracture?Ceramic multi crystal plastic deformation depends not only on th

20、e material constituting the crystal itself, but also to a great extent on the grain boundary control material, so the polycrystalline plastic deformation including the following, the dislocations caused by plastic deformation, the relative sliding between the grain and grain boundary, vacancy diffus

21、ion, viscous flow, at room temperature due to the structure characteristics of non metallic crystal and grain boundary, the plastic deformation is difficult to achieve, because the micro cracks often exist in the material, when the external stress is not enough to make the plastic deformation veloci

22、ty, the critical stress of the stress may have been more than micro crack propagation required, eventually lead to brittle materials.5. what is the rule of lattice sliding?The slip distance must be integer times of lattice constant; crystal slip in the middle always occurs in the main crystal surfac

23、e and main crystal orientation; slip occurred in the shear stress under the action of the sliding surface only when the shear stress exceeds the critical shear stress, can slip along the crystal surface.6. what are the causes of crack initiation and rapid propagation in ceramic materials? What are t

24、he measures to prevent crack propagation?Production: the development of micro defects into the crystal crack; surface mechanical strength and chemical corrosion damage formation of surface cracks caused by thermal stress; crack; crack gas formation; crystal growth or amorphous to crystal transition

25、of crack formation. Because dynamic crack propagation, when C increases, G increases, and #=4r is a constant, therefore, once they reach a critical size and initial fracture initiation and propagation of failure process is a critical stage, because of brittle material basically did not absorb large

26、amounts of energy of plastic deformation measures: the use of stress does not exceed # device settings in energy absorption; materials; artificially caused a lot of very fine is smaller than the critical size crack in the material7. what are the factors that affect thermal conductivity?Influence of

27、temperature; the influence of microstructure; the influence of chemical composition; the influence of porosity; the thermal conductivity of multiphase ceramics8 glass is a disorder network structure, it is impossible to have a slip system is brittle, but at high temperatures can deformation? Why?Ans

28、wer: it is because of the non long-range order, many atoms are not in the potential curve trough; some bond is weak, only small stress can make the bond breaking of these atoms; the gap position near the atomic transition, caused by atomic migration and rearrangement, without the initial yield stres

29、s to deformation of viscous flow.9, the reason of ferromagnetic domain formation is explained from the viewpoint of energyAnswer: according to the laws of thermodynamics, the steady-state magnetic state must be corresponding to the total free ferromagnetic material within the energy minimum state, f

30、ormation and stability of structure of a domain is corresponding to the total free energy to meet the minimum conditions. For ferromagnetic materials, the energy is reduced before splitting into domains. Therefore, when the ferromagnetic material is magnetized spontaneously, it will inevitably be di

31、vided into magnetic domains in the small region, which makes the total free energy the lowest and satisfies the minimum energy principle. It can be seen that the demagnetizing field is the reason for the formation of magnetic domains.Analysis questionsThe causes of cracks and their fracture mechanis

32、ms are briefly described. How can crack propagation be prevented?Answer: cause: because of the defects in the crystal microstructure, when subjected to external force, these defects caused by stress concentration, resulting in crack nucleation of a grains with different orientations B Journal of ato

33、mic stress concentration C thermal defectsMechanical damage and chemical corrosion on the surface of the material form surface cracksCracks formed due to thermal stressThe mechanism of crack or defect: Griffith believed that many of the small total actual material, under the action of external force

34、, near the crack and defect will result in stress concentration phenomenon, when the stress reaches a certain level, the crack began to rupture propagation.Prevention: first, the action stress should not exceed the critical stress so that the crack will not expand; secondly, the energy absorption me

35、chanism is set up in the materialWhat are the characteristics of the 2 ferroelectric? Describe the formation of an electric domain Examples are given of ferroelectric applicationsFerroelectric properties: dielectric, nonlinear, and grain boundary effectsThe formation process of domain: a natural for

36、m of many tiny areas or ferroelectric ceramic ferroelectric single crystal grain orientation, electric moment all cell in each region is the same, and electric moment orientation in the neighboring region are different, this region is called domainApplications: a boundary layer (or grain boundary la

37、yer) capacitor can be fabricated by using the grain boundary effect of semiconducting ceramics3 analyze the influence of various micro mechanisms on the dielectric constantAnswer: the material with positive and negative particles, such as electrons and ions have displacement under the influence of e

38、lectric field, the formation, dipole moment, or by turning to exhibit macroscopic polarization, the process can be divided into two kinds: first, elastic, instant finish, relaxation the polarization does not consume energy. Therefore, the mechanisms of electrical polarization include electron displa

39、cement, polarization, ion displacement polarization, and electron and ion relaxation polarization.Therefore, there are electron displacement, polarization, ion displacement polarization, electron and ion relaxation polarization, space charge polarization and steering polarization. Through the materi

40、al polarization, polarization P and dielectric constant of R and the relationship between the 3: P= anti E (anti 3r-1), anti P= 3E analysis shows that the polarization of the material to the dielectric constant is large, so the material will improve the polarization of the dielectric constant, but d

41、ue to various polarization phenomenon when different, whether can the polarization and the polarization mechanism of the electric field frequency, electron polarization time is short, the polarization range of DC and optical frequency and optical frequency is higher than the electric field can make

42、the electronic displacement polarization and electric field is smaller than the optical frequency can make the electron displacement polarization, so its effect on the dielectric constant of the main DC and optical frequency, similarly, ion displacement polarization and polarization relaxation: spac

43、e charge polarization in DC and infrared and ultra high frequency, DC, DC and high frequency on the dielectric constant of the, The influence of displacement polarization is less than relaxation polarization.4 compare the piezoelectric, ferroelectric, pyroelectric, electrostrictive differences and r

44、elationsA: dielectric properties of dielectric materials include dielectric, piezoelectric, ferroelectric, and pyroelectric propertiesPiezoelectricity: the capacity of certain crystalline materials to produce a charge proportional to the applied mechanical stressFerroelectricity: spontaneous paralle

45、l arrangement of electrical dipoles due to their interactionElectrostrictive: the magnetization of a ferromagnetic magnet in the demagnetizing state. In general, its size and shape change. This phenomenon is called electrostrictivePyroelectric (TL): certain crystals are affected by changes in temper

46、ature and produce surface charges in a certain direction of the crystal due to a corresponding change in spontaneous polarizationAnalyzing the nature of thermal expansion of solid materials, what is called polarization strength? Write out its several expressions and their physical meaningsA: the phy

47、sical properties of thermal expansion of solid materials can be attributed to the fact that the mean distance between particles increases with increasing temperature in a lattice structurePolarization strength: the total electric dipole moment in a unit volume is called polarization intensity, expre

48、ssed in PThe P= anti 3u/v unit is Kulun / m2 and the surface charge density is the sameIf the medium per unit volume polarization quality points equal to N, because each dipole dipole moment has the same direction (potential direction), so that the available vector and scalar replacement; P= n=n Elo

49、c alpha, Mu average dipole moment for each particle, of certain materials, N and alpha, is P and E is proportional to the average electric field, P= 3oXE6 what is ionic relaxation polarization and ion displacement polarization?Answer: ion relaxation polarization: if the polarization of the contact ion moves from one equilibrium position to another, when the external electric field is removed, the ion can not return to its original equilibrium position and is obviously irreversibleIon displacement polarization: a pair of ions with + Q charge, the mass is M+M-, and the center is a, and the