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An Introduction to Materials
Published in Paul J. Hazell, Armour, 2023
where E is defined as the modulus of elasticity or Young’s modulus of the material. This relationship was originally discovered by Robert Hooke in 1678 and is sometimes referred to as Hooke’s law. At an atomic level, ε is a measure of the increase (or decrease) in atomic spacing due to the applied load. As the load is increased,the inter-atomic spacing increases,and when the load is removed,the atoms return to their equilibrium position. The greater the attraction between atoms—that is,the stronger the bonding—the greater the load required to increase the inter-atomic spacing. Certain ceramic armour materials are good examples of materials with high values of E due to their strong atomic bonding. Materials with relatively weak ionic bonding tend to possess relatively low values of E.
Liquid-Crystal Nanomaterials: Introduction, Design and Properties
Published in Uma Shanker, Manviri Rani, Liquid and Crystal Nanomaterials for Water Pollutants Remediation, 2022
Anas Saifi, Charu Negi, Atul Pratap Singh, Kamlesh Kumar
To explore nature and develop structural knowledge about nanomaterials, it is important to comprehend their thermal properties. For instance, studying the melting points can help us in understanding the underlying interactions between NPs and high-density grain boundaries. Studies on thermal conductivity help in revealing the information related to the heat resistance reflection of phonons from grain boundaries and the interfaces. Apart from theoretical and fundamental significance, it is necessary to measure and study the thermal properties of nanomaterials for applications. Nanomaterials with low thermal conductivities find their use as insulators. Also, the thermal properties govern their use in thermoelectric conversion (Zhang 2018). The modulation in surface energy and inter-atomic spacing as a function of size affects the material properties of nanomaterials. In the case of bismuth NPs, the melting point, which is a bulk thermodynamic property, has been found to decrease abruptly for particle sizes lesser than 10 nm, as illustrated in Figure 12 (Roumanille et al. 2017). It has also been shown that the melting point of metallic nanocrystals which are embedded into a continuous matrix have higher melting points for smaller particle size (Putnam et al. 2006, Thangadurai et al. 2020).
Electronic Structure and Properties
Published in Alan Cottrell, An Introduction to Metallurgy, 2019
Electrons in the atomic cores cannot give ferromagnetism because they are in filled shells. The outer valency electrons also cannot because they are in states similar to the bonding state of hydrogen and because the density of these states is low. The partly-filled d states of the transition metals are favourable, however, and these metals are either ferromagnetic or strongly paramagnetic. The atomic spacing is critical. If the atoms are too far apart, the exchange interaction is too weak to resist thermal agitation, which throws the spins out of alignment. If they are too close, the exchange interaction changes sign and the kinetic energy factor increases. Conditions are most favourable when the atomic radius is 1.5 to 2.0 times greater than the radius of the atomic d shell. In the iron group of metals we have the following ratios of atomic to shell radii: TiCrMnFeCoNi1.121.181.471.631.821.98
Phonon-assisted pressure-dependent opto-electronic properties in a CdS/CdSe/CdS asymmetric quantum well
Published in Phase Transitions, 2021
R. Arulmozhi, John Peter Amalorpavam
The one-dimensional confinement of the charge carriers in the quantum wells shows exotic electrical and optical properties due to the confinement effect. The change in confinement brings out the creation of discrete energies in the wells. The latest fabrication technologies can produce the desired sizes of requirement in any low-dimensional semiconductor system. The wells having different confining potentials will lead to various potential applications of electro-optical devices such as laser diodes, infrared detectors, light-emitting diodes, high competence solar cells, modulators, etc., [1–4]. Numerous physical characteristics of reduced dimensional semiconductors such as quantum wells, quantum well wires and quantum dots are changed with the applications of hydrostatic pressure. In particular, the lattice constant, inter-atomic spacing, structural phase and band structure are modified by the application of pressure. In this aspect, there have been many researches devoted to pressure-dependent experimental and theoretical works in order to support the modern high-speed opto-electronic devices [5–7]. Any optical spectrum with the interband optical transition can be modulated with the application of hydrostatic pressure. The studies on the effects of hydrostatic pressure have proved to be an important tool in any low-dimensional semiconductor system [8–10].