CONTENTS valence electrons

Remarks on the alloy crystal chemistry of the 11th group metals. A selection of the phases formed in the binary alloys of Cu, Ag and Au and of their crystal structures is shown in Tables 5.54a and 5.54b. For a number of these phases, more details (and a classification in terms of Hume-Rothery Phases ) are given in 4.4.5 and in Table 4.5 (structure types, valence electron concentration, etc.). Table 5.54a and 5.54b show the formation of several phases having a high content... 

When a series of solid solutions between Cu and Ni is formed, it is observed that the spontaneous magnetization decreases linearly with increasing Cu content until no spontaneous magnetization remains at 60 at % Cu (see Figure 6.58). At this composition, we have added about 0.54 electrons to the d band and about 0.06 electron to the band. But the 0.54 electron added to the d band in Figure 6.57 will fill both d subbands, and the magnetization will be zero. The 10.6 total valence electrons per atom are now equally divided between spin up and spin down, as shown in Figure 6.59. 

Hydrogen, lithium and other intramolecular bonds or intermolecular ones are by their origin secondary chemical bonds. Strong chemical bonds result from a primary act of interaction of atoms, whereas weak chemical bonds appear as a result of alteration in their valence states on condition that the energy content of valence electrons of those atoms can provide for the formation of new chemical bonds. 

For DBES data three main factors contribute to the S parameter in polymers (1) free-volume content, (2) free-volume size, and (3) chemical composition. First, larger free-volume content contributes to a larger S value. DBES measures radiation near 511 keV where a major contribution comes from p-Ps. This p-Ps contribution is only 1/3 the o-Ps intensity as that in I3 of PAL data. Second, when p-Ps is localized in a defect with a dimension fix, the momentum Ap has a dispersion according to the Heisenburg uncertainty principle AxAp > h/4n. The S parameter from DBES spectra is a direct measure of the quantity of momentum dispersion. In a larger size hole where Ps is localized, there will be a larger S parameter due to smaller momentum uncertainty. Therefore, in a system with defects or voids, such as polymers, the S parameter is a qualitative measure of the defect size and defect concentration. The value of the S parameter also depends on the momentum of the valence electrons, which annihilate with the positrons. The absolute value of the S parameter therefore, may differ from polymer to polymer. Third, the S parameter depends on the electron momentum of the elements. As the atomic number of the elements increases, the electron momentum increases, and thus the S parameter decreases. Fortunately, in chemicals of... 

It is obvious that the stability of the NaCl-type phase in these solid-solution systems increases with the content of NbN or ZrN, whose number of valence electrons is one or two less than that of MoN. That is to say, the stability of the NaCl-type phase in these systems decreases with increasing the number of valence electrons, Ny. In the higher Ny regions, the NaCl-type phase in the MoN-NbN system transforms to the WC-type phase in NH3 gas and to y-Mo2N-type phase in N2 gas. These phase transformations take place in the samples with x < 0.5, ie., Ny > 10, of the Moj Zr N and in the samples with X < 0.38, ie., Ny > 10.38, of the Moj jjNb,(N system. The annealed Nb-rich films showed a small reduction in lattice parameter, although the NaCl-type structure was remained until 1173K. 

Direct attacks, either all-electron or 22 valence-electron model-potential approaches, have clearly pointed out the need for extended basis sets, an extensive treatment of d-electron correlation and the inclusion of relativistic corrections if one aspires to high accuracy. Since there are so many papers on Cu2 and since many of them, of course, arrive at similar conclusions, I will be content with a brief review of five of the ab initio papers which I believe present the essential features. 

Modifications. It should be noted that both of the solvent elements, copper and silver, are monovalent, i.e. they both have atoms in which there is only one outer-layer or valency electron, while the solute elements, zinc, magnesium, cadmium and berylium, are all divalent, i.e. they all have atoms with two outer-layer or valency electrons. We shall soon be in a position to show how important in alloy structures these valency electrons can be we must content ourselves for the moment, however, by stating that Hume-Bothery has examined the solid solubility of various metals in the divalent solvent magnesium, and has shown that the favourable size-factor principle may be equally well applied to magnesium alloys, typical of... 

Many of the transition metal carbides such as TiC and ordered VC ( are very hard compounds. In 8TiCi ( the microhardness increases with increasing carbon content [97], a phenomenon that is probably closely related to the valence electron concentration (VEC) with a maximum stability at VEC = 8 at the composition TiC. 

Another contribution involved the measurement of the high-temperature heat contents of the rare earth metals. An analysis of the data revealed that the entropy of transformation, AS, for the close packed to bcc transformation in the rare earth metals depended upon the number of valence electrons (Dennison et al. 1966c), i.e. AS,r 0.2 e.u. per valence electron. Extension of these observations to the remainder of the periodic table indicated that the entropy of transformation of metals which posses two or more of the common metallic structures and the entropy of fusion depend upon both the crystalline structure of the phases involved and the number of valence electrons (Gschneidner 1975). These results were then used to predict the entropies of fusion for 16 metals, including two lanthanide metals - promethium and lutetium - and the entropies of transformation of 5 metals including promethium, for which no reliable experimental values existed. 

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