TABLE OF CONTENTS The resistivities of a number of pure metals and alloys are given in Tables 19.1 to 19.4. Resistivity varies with the condition of the material and is sensitive to purity. In general, cold working increases and annealing decreases the resistivity. Common reactive gases such as oxygen, nitrogen and hydrogen may also affect the resistivity, either through selective chemical action with existing metallic impurities (which may even reduce the resistivity) or through solution in the host matrix itself.1 Thermal cycling through phase transformation, quenching from high temperatures and irradiation, all introduce lattice defects which increase resistivity. These defects include vacancies, dislocations and interstitial atoms. Annealing will promote the movement and eventual removal of these defects. This recovery generally takes place in discrete stages at certain temperatures corresponding to the annealing out of each type of defect. Recovery is complete after treatment at the recrystallisation temperature.
Resistivity is often expressed approximately as the sum of the residual resistivity at absolute zero (arising from impurities and lattice defects) and a temperature-dependent intrinsic resistivity (arising from the effect of lattice vibrations upon conduction electrons). The form of temperature dependence is complex, and theories governing it in both solid and liquid metals have been recently discussed in, for example, references 2 15. Over a limited temperature interval, resistivity may be conveniently expressed as a linear relation of the form ? 1 = ? 0(1 + ? T), where T is the interval between two temperatures T 1 and T
