MindMap Gallery Materials Electricity
This is a mind map about the electricity of materials, including energy band theory, dielectric properties of materials, conductivity of materials, etc.
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This is a mind map about bacteria, and its main contents include: overview, morphology, types, structure, reproduction, distribution, application, and expansion. The summary is comprehensive and meticulous, suitable as review materials.
This is a mind map about plant asexual reproduction, and its main contents include: concept, spore reproduction, vegetative reproduction, tissue culture, and buds. The summary is comprehensive and meticulous, suitable as review materials.
This is a mind map about the reproductive development of animals, and its main contents include: insects, frogs, birds, sexual reproduction, and asexual reproduction. The summary is comprehensive and meticulous, suitable as review materials.
Materials Electricity
conductivity of material
Electronic conductivity
Material conductivity ranking
Superconducting materials: s under superconducting conditions Conductor material: s>104 S/m Semiconductor materials: 10-3<s<104 S/m Insulation material: s< 10-3 S/
Electronic conductivity
The conductivity of a material refers to the directional movement of charged particles in the material under the action of an electric field, thereby forming a macroscopic current, which belongs to the charge transport characteristics of the material.
The conductivity of an object is related to the microscopic particles in the material that participate in conduction.
The microscopic nature of conduction: directional migration of carriers under the action of electric field
J=nqv σ=J/E=nqv/E
μ=v/E: The mobility of carriers, its physical meaning is the average drift velocity of carriers under unit electric field
Multiple carriers
σ=nqμ
According to the type of carrier
Electron carriers conduct electricity
electrons, holes
Ionic carrier conduction
Positive ions, negative ions
The carriers in a solid can include: electrons, holes, positive ions, and negative ions. The mechanism of conduction: directional migration of carriers.
Basic characteristics of electronic conductivity
Hall effect
Pass the current I (current density Jx) along the x-axis direction of the sample, and add a magnetic field (magnetic induction intensity Bz) in the Z-axis direction, then a potential difference (transverse electric field Ey) will be generated in the y-axis direction.
For p-type semiconductors, when an electric field Ex is applied along the Charge accumulation generates the "Hall electric field Ey", which has the following relationship when stable:
P-type semiconductor Hall coefficient: RH=1/(pq)>0 N-type semiconductor Hall coefficient: RH=-1/(nq)<0
magnetoresistive effect
Refers to the phenomenon that the resistance value of certain metals or semiconductors changes with the change of external magnetic field. The rate of change in resistivity is called magnetoresistance (MR)
Classification by mechanism
physical magnetoresistive effect
Statistical distribution of carrier velocities causes resistivity to vary with magnetic field
geometric magnetoresistive effect
The existence of the Hall effect increases the actual path of the current, which is equivalent to an increase in resistivity.
Metal conducts electricity
Conductivity obtained from classical free electron theory:
Conductivity obtained by quantum free electron theory:
Conductivity obtained from band theory:
ionic conductivity theory
ionic conductivity
Electronic conductivity, conduction with electron carriers as the main body. electron scattering Ionic conductivity, conduction with ion carriers as the main body. ion diffusion Mixed conductivity has both electrons and ions as carriers. Directional carrier migration
Ionic conduction: the directional movement of charged ion carriers under the action of an electric field
Electrolysis effect: When ions conduct conduction and migrate, electrons gain and lose near the electrode, accompanied by the electrolysis phenomenon of the production of new substances.
Faraday's law: g=CQ=Q/F
intrinsic conductivity
High temperature conditions can occur
Basic ions leave the crystal lattice with thermal vibrations to form thermal defects (such as Schottky defects, Frenkel defects). Thermal defects (ions or vacancies) are electrically charged and can act as ionic conductive carriers.
Impurities conduct electricity
Lower temperatures can occur
Impurity ions are weakly bonded ions in the crystal lattice. At lower temperatures, the movement of weakly bonded impurity ions causes electrical conduction.
Superconductivity of materials
Superconducting microscopic theory explains superconducting phenomena
quantum tunneling effect
Electrons have the ability to pass through potential barriers higher than their own energy. Of course, the probability of penetration decreases rapidly as the height and width of the barrier increase.
ferroelectricity of materials
The mechanism of dielectric breakdown
ferroelectric phenomenon
It has spontaneous polarization within a certain temperature range and the polarization can be reoriented with changes in the external electric field, which is called ferroelectricity. Materials with ferroelectric properties are called ferroelectric materials or ferroelectrics.
Main characteristics of ferroelectric materials:
energy band theory
Matheson's law: The resistance of a metal includes basic resistance and residual resistance caused by impurity concentration.
ρ=ρ(T) ρ_r
dielectric properties of materials
Dielectrics and their polarization
polarization phenomenon
In a charge-bound system, the separation of the centers of gravity of positive and negative charges is polarization.
Dielectric polarization in plate capacitors
Dielectric: A substance that can establish polarization (bound charge plays a major role) under the action of an electric field. The phenomenon that a dielectric produces induced charges under the action of an electric field is called polarization of the dielectric.
Electric dipole and electric dipole moment
Electric dipole: A bound system composed of two point charges (q, −q) of equal magnitude, opposite sign, and equidistant l from each other.
μ=q∙l
Dielectrics and their polarization
Non-polar dielectric: the positive and negative charge centers in the molecule overlap, such as: helium (He), hydrogen (H2), methane (CH4), etc.
Polar dielectric: The centers of positive and negative charges in the molecule do not overlap, but there is a certain distance between them. Such as: water (H2O), hydrogen chloride (HCl), ammonia (NH3), methanol (CH3OH), etc.
Electrical polarization is also the surface charge density:
Electrical susceptibility: the electric field intensity generated by free charges E0:
Microscopic mechanism of dielectric polarization
Ion polarization-ion displacement polarization
Polarization caused by ions shifting from their equilibrium position under the action of an electric field. It is equivalent to forming an induced dipole moment. From the classical elastic vibration theory, the ion polarizability can be calculated:
electron relaxation polarization
ion relaxation polarization
Characteristics of relaxation polarization
Four microscopic mechanisms of electric polarization
electron displacement polarization
ion displacement polarization
dipole orientation polarization
space charge polarization