Material conductivity ranking

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

Electron carriers conduct electricity

Ionic carrier conduction

The carriers in a solid can include: electrons, holes, positive ions, and negative ions. The mechanism of conduction: directional migration of carriers.

Hall effect

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:

magnetoresistive effect

Conductivity obtained from classical free electron theory:

Conductivity obtained by quantum free electron theory:

Conductivity obtained from band theory:

ionic conductivity

intrinsic conductivity

Impurities conduct electricity

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.

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.

ρ=ρ(T) ρ_r

In a charge-bound system, the separation of the centers of gravity of positive and negative charges is polarization.

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: A bound system composed of two point charges (q, −q) of equal magnitude, opposite sign, and equidistant l from each other.

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.

Ion polarization-ion displacement polarization

electron relaxation polarization

ion relaxation polarization

Four microscopic mechanisms of electric polarization