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Symbols, Terminology, and Nomenclature
Published in W. M. Haynes, David R. Lide, Thomas J. Bruno, CRC Handbook of Chemistry and Physics, 2016
W. M. Haynes, David R. Lide, Thomas J. Bruno
Partition function (q, z) - For a single molecule, q = i giexp(i/kT), where i is an energy level of degeneracy gi, k the Boltzmann constant, and T the absolute temperature; the summation extends over all energy states. For a system of N non-interacting molecules which are indistinguishable, as in an ideal gas, the canonical partition function Q = qN/N!. Pascal (Pa)* - The SI unit of pressure, equal to N/m2. [1] Paschen series - The series of lines in the spectrum of the hydrogen atom which corresponds to transitions between the state with principal quantum number n = 3 and successive higher states. The wavelengths are given by 1/ = RH(1/9-1/n2), where n = 4,5,6,... and RH is the Rydberg constant. The first member of the series (n = 34), which is often called the P line, falls in the infrared at a wavelength of 1.875 µm. Paschen-Back effect - In atomic spectroscopy, the decoupling of electron spin from orbital angular momentum as the strength of an external magnetic field is increased. Pauli exclusion principle - The statement that two electrons in an atom cannot have identical quantum numbers; thus if there are two electrons in the same orbital, their spin quantum numbers must be of opposite sign. Pearson symbol - A code for designating crystallographic information, including the crystal system, the lattice type, and the number of atoms per unit cell. Péclet number (Pe) - A dimensionless quantity used in fluid mechanics, defined by Pe = vl/a, where v is velocity, l is length, and a is thermal diffussivity. [2] Peltier effect - The absorption or generation of heat (depending on the current direction) which occurs when an electric current is passed through a junction between two materials. Peptides - Amides derived from two or more amino carboxylic acid molecules (the same or different) by formation of a covalent bond from the carbonyl carbon of one to the nitrogen atom of another with formal loss of water. [5] Permeability (µ) - Magnetic induction divided by magnetic field strength; i.e. µ = B/H. The relative permeability µr = µ/µ0, where µ0 is the permeability of a vacuum. [1] Permittivity () - Ratio of the electric displacement in a medium to the electric field strength. Also called dielectric constant. [1] Peroxides - Compounds of structure ROOR in which R may be any organic group. In inorganic chemistry, salts of the anion O2-2 [5] Peroxy acids - Acids in which an acidic -OH group has been replaced by an -OOH group; e.g., CH3C(=O)OOH peroxyacetic acid, PhS(=O)2OOH benzeneperoxysulfonic acid. [5] Petroleum ether - The petroleum fraction consisting of C5 and C6 hydrocarbons and boiling in the range 35-60 °C; commonly used as a laboratory solvent. pH* - A convenient measure of the acid-base character of a solution, usually defined by pH = -log [c(H+)/mol L-1)], where c(H+) is the concentration of hydrogen ions. The more precise definition is in terms af activity rather than concentration. [2] Phenols - Compounds having one or more hydroxy groups attached to a benzene or other arene ring. [5] Phonon - A quantum of energy associated with a vibrational mode of a crystal lattice. Phosphines - PH3 and compounds derived from it by substituting one, two or three hydrogen atoms by hydrocarbyl groups.
The Hume-Rothery electron concentration rule studied through interference phenomena in a series of cP12 compounds with either a true gap or pseudogap across the Fermi level
Published in Philosophical Magazine, 2020
Tomoyuki Homma, Uichiro Mizutani, Hirokazu Sato
The cP12 compounds studied in the present work are listed in Table 1. It is clear that they can be grouped into two, depending on the value of VEC equal to 14/3 or 20/3, although they are isostructural under the same Pearson symbol cP12 and the space group (No.205). It is re-emphasised that they are either insulators or metals with a deep pseudogap at the Fermi level. It has been pointed out [2] that the absolute difference of Allen's electronegativities between the constituent elements A and B may be used as a rough guide to judge the degree of ionicity of a compound AB. The values of for the present MX2 compounds are listed in Table 1 after multiplying a constant 40 so as to allow them to be distributed in the range from zero up roughly to 100 [1–3]. It can be seen that the ionicity parameters for As2Si and P2Si, in which the constituent elements are located next to each other in the periodic table, are very low, while those for MgO2 and O2Os are very high. We will study below how these unique characteristics are reflected in their electronic structures.
Alloying effects and site occupancies of Re in the C14 Cr-based Laves phases: a first-principles study
Published in Philosophical Magazine, 2018
Youjian Zhang, Jianxin Zhang, Pan Li, Huixin Jin, Wenyang Zhang, Shiyu Ma
The structure of the C14 Laves phases belongs to the space group P63/mmc (No. 194) and Pearson symbol hP12. There are 12 atoms in the primitive unit cells with Cr1 and Cr2 atoms occupying the geometrically inequivalent 2a and 6 h Wyckoff sites and X (X = Nb, Ta, Ti, Zr, Hf) atoms occupying the 4f Wyckoff sites. The 2a and 6 h sites present a coordination number (CN) of 12 whereas the 4f sites have the coordination number of 16. The supercell method has often been employed for calculations for intermetallic compounds with impurities [20,21]. In this paper, the 1 × 1 × 2 supercells (24 atoms) containing one ternary atom Re (the concentration of Re is 4.17 at. %) were used in consideration of getting the results close to the case of a single, isolated impurity. The chemical formula is assumed as X7ReCr16 and X8Cr15Re (X = Nb, Ta, Ti, Zr, Hf) when Re substitutes the X and Cr atoms respectively.
Structural, electronic, magnetic, elastic and thermodynamic properties of Ni 4 N anti-perovskite
Published in Phase Transitions, 2021
A. Azouaoui, M. El haoua, I. El Hamdani, N. Benzakour, K. Haboubi, A. Hourmatallah, A. Rezzouk
Hemzalová et al. in Ref. [14] calculated the structural parameters as well as elastic and electronic properties of eight allotropes of using density functional theory. In this study, Hemzalová et al. show that the FM α- with cubic structure (Pearson symbol , space group (221)) is found to be the most stable structure.