Chapter 7: Electrical Properties

One of the most important electrical characteristics of a solid material is the ease with which it transmits an electric current. ___ relates the current I—or time rate of charge passage— to the applied voltage V

Ohm’s law

The ___ ρ is independent of specimen geometry but related to R

The value of R is influenced by ___, and for many materials is independent of current.

is used to specify the electrical character of a material. It is simply the reciprocal of the resistivity

An ____ results from the motion of electrically charged particles in response to forces that act on them from an externally applied electric field. Positively charged particles are accelerated in the field direction, negatively charged particles in the direction opposite.

Within most solid materials a current arises from the flow of electrons, which is termed

for ionic materials a net motion of charged ions is possible that produces a current; such is termed

filled - highest occupied energy levels

empty - lowest unoccupied energy levels

Four possible electron band structures for solid materials The various possible electron band structures in solid at 0 K

The electron band structure found in metals such as copper, in which there are available electron states above and adjacent to filled states, in the same band

The electron band structure of metals such as magnesium, wherein there is an overlap of filled and empty outer bands

The electron band structure characteristic of insulators; the filled valence band is separated from the empty conduction band by a relatively large band gap (>2 eV)

• (conductors) • thermal energy puts many electrons into a higher energy state

The electron band structure found in the semiconductors, which is the same as for insulators except that the band gap is relatively narrow (<2 eV)

for metals nearby energy states are accessible by thermal fluctuations

higher energy states not accessible due to gap (>2 eV)

higher energy states separated by smaller gap

Because crystalline defects serve as scattering centers for conduction electrons in metals, increasing their number raises the resistivity (or lowers the conductivity). The concentration of these imperfections depends on ___ of a metal specimen.

it has been observed experimentally that the total resistivity of a metal is the sum of the contributions from___; that is, the scattering mechanisms act independently of one another.

dependence of the thermal resistivity component on temperature is due to the increase with temperature in thermal vibrations and other lattice irregularities (e.g., vacancies), which serve as

a single impurity that forms a solid solution, the impurity resistivity pi is related to the___, in terms of the atom fraction (at 100%)

also raises the electrical resistivity as a result of increased numbers of electron-scattering dislocations. The effect of deformation on resistivity