Interconfigurational energies

The interconfigurational energy AE=E(dn 1s1) — E(dn 2s2) calculated by Harris and Jones96 is shown in Figures 15a and b for the Ad and 5d series, respectively. The squares show the non spin-polarized results, the full circles the spin-polarized calculations and the triangles show the experimental values. The trends in the density calculations are seen to agree well with experimental values. Earlier work of Slater et al. considered mixed configurations Zdn xAsx of Co and Ni. 

Figure 15 Interconfigurational energy AE= E(dn 1s1)—E(dn 2s2). (a) For the 4d series, (b) For the 5d series, taken from the work of Harris and Jones.96 , Nonspin-polarized results O, spin-polarized calculations, A, experimental values...

Having presented the above caveat, we return to Fig. 5. The trends in the interconfigurational energy across the series are interpreted very well by the central-field LSD caleulations including the break between Cr and Mn. 

Fig. 5. Interconfigurational energy difference AE-,c = [3d" Ms ] — [3d" 4s ], for atoms of 3d series. Squares non-spin-polarized results full circles spin-polarized results crosses experimental values (Ref. 154). (Reproduced from Ref. 118 by permission of the authors and the American Institute of Physics.)...

The rare earth (RE) ions most commonly used for applications as phosphors, lasers, and amplifiers are the so-called lanthanide ions. Lanthanide ions are formed by ionization of a nnmber of atoms located in periodic table after lanthanum from the cerium atom (atomic number 58), which has an onter electronic configuration 5s 5p 5d 4f 6s, to the ytterbium atom (atomic number 70), with an outer electronic configuration 5s 5p 4f " 6s. These atoms are nsnally incorporated in crystals as divalent or trivalent cations. In trivalent ions 5d, 6s, and some 4f electrons are removed and so (RE) + ions deal with transitions between electronic energy sublevels of the 4f" electroiuc configuration. Divalent lanthanide ions contain one more f electron (for instance, the Eu + ion has the same electronic configuration as the Gd + ion, the next element in the periodic table) but, at variance with trivalent ions, they tand use to show f d interconfigurational optical transitions. This aspect leads to quite different spectroscopic properties between divalent and trivalent ions, and so we will discuss them separately. 

Core-level spectra are useful in studying mixed valence (valence instability or interconfigurational fluctuation) in rare-earth systems (e.g. SmS, Ce) which arises when Eexc = n (E -i + FJ 0 where( — , )istheenergydifferencebetweenthe4/ and 4T states and is the energy of the promoted electron. The time scale involved... 

Dependent Band Model for Lanthanide Compounds and Conditions for Interconfiguration Fluctuations J. N Murrell The Potential Energy Surfaces of Polyatomic Molecules J-A-Duffy Optical Electron ativity and Nephelauxetic Effect in Oxide Systems Application to Conducting, Semi-Conducting and Insulating Metal Oxides... 

The second chapter deals with quantum chemical considerations, s, p, d and f orbitals, electronic configurations, Pauli s principle, spin-orbit coupling and levels, energy level diagrams, Hund s mles, Racah parameters, oxidation states, HSAB principle, coordination number, lanthanide contraction, interconfiguration fluctuations. This is followed by a chapter dealing with methods of determination of stability constants, stability constants of complexes, thermodynamic consideration, double-double effect, inclined w plot, applications of stability constant data. 

As a final note we add that the recently reported INDO/S Cl calculations of the Cr(CO)g spectrum resulted in an intensity ratio of 1 400 for the two transitions allowed, due to the fact that with this method the interconfigurational mixing in both states is grossly overestimated. Although the calculated transition energies reported, 4.60 eV and 5.79 eV, conformed with experiment, both states were in fact calculated as an almost equal mixture of and 2lg2t. ... 

The pressiue dependence of the electrical resistivity of YbCuAl was investigated (Alami-Yadri et al. 1998, 1999a,b) up to 8 GPa. The resistivity at 300 K decreases with increasing pressure. At 8 GPa a dependence occurs at low temperature (Fermi-liquid behavior), and the Kondo temperature decreases with increasing pressure. The experimental setup for these measurements was presented by Jaccard et al. (1998). Furthermore, point-contact spectroscopy was used to measure the interconfigurational excitation energies and conduction-electron lifetime width of valence-fluctuating YbCuAl (Bussian et al. 1982). 

Fig. 1. Schematic energy level diagram of the in-terconfigurational fluctuation (ICF) model describing valence fluctuations between two 4f configurations (4r, 4r ), characterized by their /multiplet level structure. The basic parameters of the ICF model and denote the interconfigurational excitation energy and interconfigurational mixing width, respectively.

Fig. 8. Temperature dependence of (a) the interconfigurational excitation energy ( ,) and (b) the upper limit of the fluctuation temperature T, of EuPd Sij as directly revealed in the Raman spectra of fig. 5.

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