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  • Chemistry  (15)
  • 61.70  (5)
  • Rare earth elements  (2)
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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 30 (1983), S. 117-122 
    ISSN: 1432-0630
    Schlagwort(e): 61.70 ; 72.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Fluctuations in the number of vacancies in metals in thermal equilibrium lead to resistivity fluctuations. Analysis of these fluctuations permits measurement of both formation and migration enthalpy of the vacancies. The power spectrum of the fluctuations is calculated using a series of statistically independent pulses. It can be derived from the diffusion equation for any geometry of the vacancy sinks. Vacancy diffusion to the surface of a thin plate or of a sphere are treated as examples. The measurability of vacancy noise is assessed. It should also be possible to measure vacancy noise during irradiation. It is predicted that correlated vacancy creation, which may occur during irradiation, will cause an increase in the power spectrum.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 22 (1980), S. 185-187 
    ISSN: 1432-0630
    Schlagwort(e): 06 ; 07 ; 61.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract New methods for thermal-equilibrium investigations of atomic vacancies or of dislocation movements in metals require measurements of minute resistance fluctuations. The accuracy of such measurements is limited by thermal noise from the resistor. The present paper proposes a method for analysing resistance fluctuations independent of voltage noise.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 48 (1989), S. 233-236 
    ISSN: 1432-0630
    Schlagwort(e): 06 ; 07 ; 61.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract A novel method is presented for measuring the spectral density of resistance fluctuations without the explicit determination of the voltage background noise (Johnson noise, pre-amplifier noise). The output of a standard ac bridge excited by a single-frequency alternating current is demodulated by two phase-sensitive detectors which operate in quadrature. When the phase difference between excitation and detection is properly set, the real part of the cross-spectral density of the two demodulators shows only the spectral density of the resistance fluctuations and not the disturbing background noise. The feasibility of our new method is demonstrated by measurements of 1/f noise of a thin-film A1 sample.
    Materialart: Digitale Medien
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  • 4
    ISSN: 1432-0630
    Schlagwort(e): 61.70 ; 81
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract By means of an integrated source-specimen technique the temperature dependence of positron lifetimes and annihilation lineshapes has been measured, on the same specimens of gold and cadmium from 4.2K to the melting points, and also in electronirradiated and quenched gold. The anomalous temperature dependence of positron annihilation at intermediate temperatures (200 to 350 K in Cd, 270 to 750 K in Au) discovered by Lichtenberger, Schulte, and MacKenzie is confirmed. The data are incompatible with the idea that the intermediate temperature dependence is due to thermal expansion. They are well explained by an extension of the trapping model which includes the formation of metastable self-trapped positrons. From lineshape measurements after electron irradiation at 180 K and after quenching it is deduced that the trapping rate of positrons at vacancy-type defects in Au is temperature independent below room temperature.
    Materialart: Digitale Medien
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  • 5
    ISSN: 1432-0630
    Schlagwort(e): 78.70 ; 61.70 ; 07.77
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract A slow-positron source has been installed in the therminal of an electrostatic 6.5 MeV accelerator and provides a monoenergetic positron beam in the few-MeV range. It will be used to operate a “fast” positron lifetime spectrometer based onβ + γ coincidences. The properties of the beam, the expected performance of the spectrometer, its advantages over conventionalγγ lifetime measurements, a number of intended applications, as well as recent positron-electron scattering experiments and plans for positron channelling and channelling-radiation studies are outlined.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Theoretical chemistry accounts 75 (1989), S. 369-387 
    ISSN: 1432-2234
    Schlagwort(e): Pseudopotentials ; Rare earth elements
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Nonrelativistic and quasirelativistic energy-adjusted pseudopotentials for fixed 4f subconfigurations of the rare earth elements La through Lu together with corresponding optimized valence basis sets have been used in SCF and CI(SD) calculations to determine the spectroscopic constants for the energetically low lying superconfigurations of the lanthanide monohydrides, monoxides and monofluorides. The experimentally observed trends in dissociation energies, bond lengths and vibrational frequencies for the ground states of the calculated superconfigurations of the monoxides and monofluorides are well reproduced. The results for the monohydrides are mainly predictions.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Theoretical chemistry accounts 75 (1989), S. 173-194 
    ISSN: 1432-2234
    Schlagwort(e): Pseudopotentials ; Rare earth elements
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Nonrelativistic and quasirelativistic energy-adjusted pseudopotentials and optimized (7s6p5d)/[5s4p3d]-GTO valence basis sets for use in molecular calculations for fixed f-subconfigurations of the rare earth elements, La through Lu, have been generated. Atomic excitation and ionization energies from numerical HF, as well as SCF pseudopotential calculations using the derived basis sets, differ by less than 0.1 eV from numerical HF all-electron results. Corresponding values obtained from CI(SD), CEPA-1, as well as density functional calculations using the quasirelativistic pseudopotentials, are in reasonable agreement with experimental data.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 67 (1998), S. 157-173 
    ISSN: 0020-7608
    Schlagwort(e): electron correlations ; charge fluctuations ; correlation strength ; chemical bonds ; first-row homonuclear diatomic molecules ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: We investigate, by means of ab initio calculations, the strength of electron correlations within covalent bonds: the first-row homonuclear diatomics serve as test cases. As an appropriate measure of the correlation strength, we introduce the reduction of the mean-square deviations of the electronic charges in localized orbitals forming a bond. A recently developed population analysis in terms of local operators derived from localized molecular orbitals is thereby used. The correlation-strength parameter depends only weakly on dynamical correlations as test calculations demonstrate. Therefore, the full-valence complete active space self-consistent field (CASSCF) approximation is applied in order to study the changes in the correlation strength with changing bond length for different types of bonds. A number of simple rules emerge from this discussion. In addition, we show that charge fluctuations are not only a reliable measure of intrabond correlation effects, but also can be used to monitor intraatomic quasi-degeneracy effects as well as the interdependence within multiple bonds.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67: 157-173, 1998
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 559 (1988), S. 17-26 
    ISSN: 0044-2313
    Schlagwort(e): Chemistry ; Inorganic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Beschreibung / Inhaltsverzeichnis: New Oxoaluminate KLi4[AlO4]Transparent and colourless single crystals of Kli4[AlO4] have been prepared for the first time by heating mixtures of Li5AlO4 and K2O in the ratio 1:5 [Ni-tube, 950°C, 50 d]. The structure determination [four-circle diffractometer, MoKα, 1699 of 2427 I0 (hkl), R = 7.41%, Rw = 4.3%] proves the monoclinic space group P21/c with a = 554.4(3), b = 1544.1(7), c = 1103.3(6) pm, β = 109.71(5)°, parameters see text. Characterizing are “isolated” AlO4 groups with symmetry nearly Td. The Madelung Part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN, these via Mean Fictive Ionic Radii, MEFIR, have been calculated.
    Notizen: Erstmals wurde KLi4[AlO4] durch Erhitzen innig verriebener Gemenge von Li5AlO4 und K2O im molaren Verhältnis 1:5 [Ni-Bömbchen, 950°C, 50 d] dargestellt. Wir erhielten farblose monokline Einkristalle (P21/c) mit a = 554,4(3), b = 1544,1(7), c = 1103,3(6) pm, β = 109,71(5)°.Die Struktur wurde mittels Vierkreisdiffraktometerdaten [MoKα, 1699 von 2427 I0(hkl), R = 7,41%, Rw = 4,3%] bestimmt, Parameter siehe Text. Charakteristisch sind “isolierte” AlO4-Gruppen, Symmetrie nahezu Td. Der Madelunganteil der Gitterenergie, MAPLE, und Effektive Koordinationszahlen, ECoN, diese über Mittlere Fiktive Ionenradien, MEFIR, wurden berechnet.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 564 (1988), S. 45-60 
    ISSN: 0044-2313
    Schlagwort(e): Chemistry ; Inorganic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Beschreibung / Inhaltsverzeichnis: Novel Oxoplumbates(II) with Isolated Anion Structure: Rb4[PbO3] and Cs4 [PbO3]For the first time Rb4[PbO3] have been prepared as single crystals. The structure determination (four-circle diffractometer data) [Rb4[PbO3]: 1818 I0 (hkl), MoKα, R = 6.49%, Rw = 6.83%, space group Pbca (a = 681.2(1), b = 1178.7(1), c = 1979,9(1) pm), Z = 8; Cs4[PbO3]: 3663 Io (hkl), AgKα, R = 11.35%, Rw = 9.82%, space group P21 (a = 1188.1(2), b = 734.4(1), c = 1176.2(2) pm, β = 111.52(2)°), Z = 4] proves in both cases the expected “isolated” [PbO3] groups. Comparing the oxides the arrangements of these groups shows surprising differences (see text). The Madelung Part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN, have been calculated.
    Notizen: Erstmals dargestellt wurden Rb4[PbO3] und Cs4[PbO3] in Form von Einkristallen. Nach der Strukturbestimmung mit Vierkreisdiffraktometerdaten [Rb4[PbO3]: 1818 I0 (hkl), Mokα, R = 6,49%, Rw = 6,83%, Raumgruppe Pbca (a = 681,2(1), b = 1178,7(1), c = 1979,9(1) pm), Z = 8; Cs4[PbO3]: 3663 Io (hkl), AgKα, R = 11,35%, Rw = 9,82%, Raumgruppe P21 (a = 1188,1(2), b = 734,4(1), c = 1176,2(2) pm, β = 111,52(2)°), Z = 4] liegen bei beiden Oxiden „isolierte“ [PbO3]-Gruppen von, deren Anordnung zueinander sich jedoch grundsätzlich unterscheidet, (Einzelheiten vgl. Text). Der Madelunganteil der Gitterenergie, MAPLE, und Effektive Koordinationszahlen, ECoN, werden angegeben.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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