Conductivity of Metals
The conductivity of metals refers to their ability to conduct electricity. Metals are good conductors of electricity due to the presence of free electrons that can move easily through the material. This property makes metals essential for various technological applications, such as in electrical wiring and electronic components.
7 Key excerpts on "Conductivity of Metals"
eBook - ePub- Jerry Whitaker(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
...8 Properties of Materials 8.1 Metals * Metals serve many different functions in the realization of radio frequency (RF) and microwave devices, each of which results in different requirements that must be met. Thus, the optimum metal for each application will vary widely. Considerations include a wide range of electrical, mechanical, chemical, and thermal properties. A first-order consideration in the choice of metals for many electrical applications is the electrical resistance of the metal conductor. DC resistance of a metal rod is given by R = ρ L A 8.1 where R is the resistance of the rod ρ is the resistivity of the metal L is the length of the rod A is the cross-sectional area of the rod The dc electrical properties of metals are also sometimes discussed in terms of conductivity. Conductivity is the inverse of resistivity given by σ = 1 ρ 8.2 where σ is the conductivity of the material. For most applications, high conductivity, or conversely low resistivity, is desirable. The resistivity of a number of metals is listed in Table 8.1. The tabulated data represent an average resistivity value from a number of sources. Values for resistivity of a metal can vary significantly because of small impurity differences between samples. Pure aluminum may exhibit a 5% increase in resistivity with the introduction of only 0.01% impurities, for example. Metals such as brass and Kovar are alloys and may exhibit even wider variations in properties based on the percentage of elemental metals in the composition...
eBook - ePubNanoparticles - Nanocomposites – Nanomaterials
An Introduction for Beginners
- Dieter Vollath(Author)
- 2013(Publication Date)
- Wiley-VCH(Publisher)
...10 Electrical Properties 10.1 Fundamentals of Electric Conductivity; Diffusive versus Ballistic Conductivity In a conventional metallic conductor, there is a huge number of electrons; after connecting a voltage, they move slowly from one to the other end of the wire. This is rather a drift than a directed movement. The electrons moving under the influence of an electrical field experience scattering processes leading to a change in momentum by interactions with electrons, phonons, impurities, or other imperfections of the lattice. These processes are responsible for the electric losses. Figure 10.1 displays these phenomena in a simplified way, where an Ohm ic conductor, for example, a metallic wire, is connected to an electric circuit, electrons are moving driven by the applied electric field. Figure 10.1 Electrical conduction mechanism in conventional metallic conductors. Diffusive conductance, active in this case, is characterized by scattering of free electrons in the conductor. Electric current is transported by free electrons performing a drift movement. The conventional process of electric conductivity called “diffusive conductance” is ruled by Ohm 's law (10.1) In Eq. (10.1), the quantity V is the applied voltage, I the electrical current, R the resistance, and G the electrical conductance. The validity of Ohm 's law implies that the electrical resistance depends only on the geometry and material of the conductor. The conductance of a wire depends on the geometrical parameters l, the length, and a, the cross section:. The electric conductivity σ is a material parameter. For metallic conductors the conductivity is independent of the applied voltage and the electric current, for semiconductors or insulators, the electric conductivity usually increases with increasing applied voltage. Wires with dimensions in the nanometer range or molecular dimensions do not follow Ohm 's law in any case...
eBook - ePubUnderstanding Solids
The Science of Materials
- Richard J. D. Tilley(Author)
- 2021(Publication Date)
- Wiley(Publisher)
...11 Electronic Conductivity in Solids What is n‐type and p‐type silicon? How are conducting polymers produced? What is a cuprate superconductor? Solids that allow an electric current to flow when a small voltage is applied are called conductors or semiconductors. Conductivity requires the presence of mobile charge carriers. In this chapter, solids that have reasonable numbers of mobile charge carriers present, either because of their native electronic properties, or because they have been deliberately introduced by doping, are considered. In addition, superconductors, a group of materials that appear not to use ‘normal’ conductivity mechanisms, are described. 11.1 Metals 11.1.1 Metals, Semiconductors, and Insulators One of the defining physical properties of a metal is its electrical conductivity, defined via Ohm's Law, where V is the voltage applied across the material, I is the resultant current, and R is the resistance. The resistance is proportional to the length of the material, L, and the cross‐sectional area, A : where ρ is the r esistivity. The resistivity of a solid is an intrinsic property, whereas resistance depends upon the dimensions of the sample. The conductivity of a solid is the inverse of the resistivity: Electrical conductivity in a metal is due to electrons that are free to move, i.e. gain energy, under the influence of an applied voltage. Metallic bonding allows conductivity to be understood most easily. In this model, the electrons on the atoms making up the solid are allocated to energy bands that run throughout the whole of the solid. A simple one‐dimensional band‐structure diagram, called a flat band diagram, allows the broad distinction between conductors, semiconductors, and insulators to be understood. If the number of electrons available fills an energy band completely and the energy gap between the top of the filled band and the bottom of the next higher (empty) energy band is large, the material is an insulator (Figure 11.1 a)...
eBook - ePubMeasurement, Instrumentation, and Sensors Handbook
Electromagnetic, Optical, Radiation, Chemical, and Biomedical Measurement
- John G. Webster, Halit Eren, John G. Webster, Halit Eren(Authors)
- 2017(Publication Date)
- CRC Press(Publisher)
...If electricity has great difficulty flowing through a material, that material has high resistivity. The electrical wires in overhead power lines and buildings are made of copper or aluminum. This is because copper and aluminum are materials with very low resistivities (about 20 nω m), allowing electrical power to flow very easily. If these wires were made of high-resistivity material like some types of plastic (which can have resistivities about 1 Eω m [1 × 10 18 ω m]), very little electrical power would flow. Electrical resistivity is represented by the Greek letter ρ. Electrical conductivity is represented by the Greek letter Σ and is defined as the inverse of the resistivity. This means a high resistivity is the same as a low conductivity and a low resistivity is the same as a high conductivity: Σ ≡ 1 ρ (26.1) This chapter will discuss everything in terms of resistivity, with the understanding that conductivity can be obtained by taking the inverse of resistivity. The electrical resistivity of a material is an intrinsic physical property, independent of the particular size or shape of the sample. This means a thin copper wire in a computer has the same resistivity as the Statue of Liberty, which is also made of copper. 26.2 Simple Model and Theory Figure 26.1 shows a simple microscopic model of electricity flowing through a material [ 1 ]. While this model is oversimplified and incorrect in several ways, it is still a very useful conceptual model for understanding resistivity and making rough estimates of some physical properties. A more correct understanding of the electrical resistivity of materials requires a thorough understanding of quantum mechanics [ 2 ]. On a microscopic level, electricity is simply the movement of electrons through a material. The smaller white circle in Figure 26.1 represents one electron flowing through the material. For ease of explanation, only one electron is shown...
eBook - ePubElectrical Conductivity in Polymer-Based Composites
Experiments, Modelling, and Applications
- Reza Taherian, Ayesha Kausar(Authors)
- 2018(Publication Date)
- William Andrew(Publisher)
...(12.8), more electrons in the volume unit are equal to the greater current flows that passes through the material. If the electric charge on the electrons was greater, then the applied voltage would pull harder on the electrons, speeding them up. If the average time between collisions of electrons with the stationary atoms was longer, then the electrons could get through the material quicker. If the mass of electrons is higher, their movement will be slower and take longer to get through the material. All of these cases would increase the resistivity [1, 2]. 12.2.2 Classification of Materials Based on Resistivity and Energy Band Structure Solid materials exhibit an amazing range of electrical conductivity, extending over 27 orders of magnitude. In fact, one way to classify solid materials is to classify them according to how the material is transported electricity from itself. The materials can be classified as insulators, semiconductors and conductors. Metals with resistivity on the order of 10 −7 (Ωm) are good conductors. Copper and aluminum are the good examples of a conductor. At the other extreme are materials with very high resistivity, ranging between 10 10 and 10 20 (Ωm); these are electrical insulators. The glass, wood, and plastic are the examples of an insulator that do not conduct current. Semiconductor materials have intermediate resistivity from 10 −4 to 10 6 (Ωm). They classified between the conductors and insulators. The silicon and germanium are the examples of a semiconductor [3]. In all conductors, semiconductors, and many insulating materials, the magnitude of the electrical conductivity is strongly depend on the number of electrons available to participate in the conduction process. Only electrons that exist in conduction band can participate in the conduction process. However, not all electrons in every atom will accelerate in the presence of an electric field...
eBook - ePubMaterials
Engineering, Science, Processing and Design
- Michael F. Ashby, Hugh Shercliff, David Cebon(Authors)
- 2009(Publication Date)
- Butterworth-Heinemann(Publisher)
...The conductivity κ e is the reciprocal of this: κ e = 2 × 10 7 S/m. The charge carried by an electron is e = 1.6 × 10 −19 Coulombs (see inside front cover of this book). The volume of the unit cell of copper is Each unit cell contains two copper atoms, each of which contributes two mobile electrons. Thus the density of mobile electrons is n v = 8.57 × 10 28 per m 3. Thus the electron mobility is Metals are strengthened (Chapter 7) by solid solution hardening, work hardening or precipitation hardening. All of these change the resistivity too. By ‘zooming in’ on part of the strength–resistivity chart, we can see how both properties are affected— Figure 14.11 shows this for two of the best conductors: copper and aluminum. Adding solute to either metal introduces scattering centers, increasing the electrical resistivity. Dislocations add strength (by what we called work hardening) and they too scatter electrons a little, though not as much as solute. Precipitates offer the greatest gain in strength; their effect on resistivity varies, depending on their size and spacing compared to the electron mean free path and on the amount of residual solute left in the lattice. Precipitation hardening (with low residual solute) or work hardening is therefore the best way to strengthen conductors. The two figures show that commercial conductor alloys have much greater strength, and only slightly greater resistivity than the pure metals. Figure 14.11 The best choice of material for a cable is one with high strength and low resistivity, but strengthening mechanisms increase resistivity. Work hardening and precipitation hardening do so less than solute hardening. The resistivity of metals increases with temperature because thermal vibration scatters electrons. Resistance decreases as temperature falls, which is why very-high-powered electromagnets are pre-cooled in liquid nitrogen...
eBook - ePub- Adrian Waygood(Author)
- 2018(Publication Date)
- Routledge(Publisher)
...Judging from his meticulous and extensive research notes, Cavendish must have subjected himself to thousands of such shocks! And, rather surprisingly, his results apparently compare remarkably well with what we know today about the electrical resistance of various materials. Resistance (symbol: R) is, to some extent, dependent upon the quantity of free electrons available as charge carriers within a given volume of material, and the opposition to the drift of those free electrons due to the obstacles presented by fixed atomic structure and forces within that material. For example, conductors have very large numbers of free electrons available as charge carriers and, therefore, have low values of resistance. On the other hand, insulators have relatively few free electrons in comparison with conductors, and, therefore, have very high values of resistance. But resistance is also the result of collisions between free electrons drifting through the conductor under the influence of the external electric field, and the stationary atoms. Such collisions represent a considerable reduction in the velocity of these electrons, with the resulting loss of their kinetic energy contributing to the rise of the conductor’s temperature. So it can be said that the consequence of resistance is heat. The consequence of resistance is heat. Resistance, therefore, can be considered to be a useful property as it is responsible for the operation of incandescent lamps, heaters, etc. On the other hand, resistance is also responsible for temperature increases in conductors which result in heat transfer away from those conductors into their surroundings – we call these energy losses, which, of course, are undesirable. We can modify the natural resistance of any circuit by adding resistors. These are circuit components, which are manufactured to have specific values of resistance...
