A. Freimuth

Correlation between transport properties and quasielastic linewidths of Ce and Yb compounds with unstable 4f-shell

Abstract From an analysis of available data it is shown that there is experimental evidence for a rather general correlation of electrical resistivity, ϱ, and thermopower with the quasielastic linewidth of the neutron spectra, Γ QE , for intermetallic Ce- and Yb-compounds with an unstable 4f-shell. At high temperatures, k B T > Γ QE , the 4f-contribution to the resistivity, Δϱ, scales with Γ −1 QE . For Ce-compounds, which show a resistivity maximum, the measured strong temperature dependence of Γ QE corresponds to the temperature dependence of the resistivity above the resistivity maximum over a few hundred K. Empirical expressions for resistivity and thermopower are presented, which not only yield the observed correlation for k B T > Γ QE , but which also describe the low temperature decrease of the two quantities: Fits for the resistivities and the thermopowers of a large number of Ce- and Yb-compounds are is very good agreement with the data over a large range of temperatures. The correlation as well as the empirical expressions for resistivity and thermopower are discussed within a model of M. Weger, which has recently been proposed to account for the so called “resistivity saturation” observed in materials with narrow bands.

Specific heat, magnetic susceptibility and transport properties of polycrystalline CeInAu and CeInAu2

Abstract Measurements of specific heat (1.4–350 K), thermopower and thermal conducctivity (1.5–300 K), electrical resistivity (40 mK–300 K) and of the magnetic susceptibility (40 mK–300 K) on polycrystalline samples of CeInAu, CeInAu2 and of the reference compounds LaInAu and LuInAu2 are reported. The properties of the Ce-compounds are unusual due to phase transitions (magnetic ordering, martensitic) and crystalline electric field effects. There are only weak indications of a valence instability.

Incipient valence instability of dilute Pr in Pd

Abstract At 300 K the L III valence of dilute Pr in Pd is 3.10. At helium temperatures the susceptibility shows an effective moment close to the Γ 5 crystal field groundstate of Pr 3+ but with a characteristic temperature of 1.6 K which implies a nonmagnetic impurity groundstate. The impurity resistivity has a minimum and the thermopower a maximum at 20 K. Above 100 K the effective impurity moment is strongly enhanced by magnetic polarization of the Pd matrix.

Resistivity anomalies due to charge fluctuations

Abstract The electrical resistivity is calculated within Wohllsbens dynamic alloy model. It is shown that the Coulomb scattering of conduction electrons on charge fluctuations in valence fluctuating materials can be responsible for the observed resistivity anomalies.

Pr-Instabilities in (ZrPr)B12

Abstract Measurements of magnetic susceptibility, specific heat, transport properties and L III -absorption edges are reported for (RE x ZR 1-x )B 12 , RE = Ce, Pr, Tb. The thermodynamic properties indicate an incipient valence instability of Pr and Ce, although the L III valence is very close to three. The experimental data for Pr can be understood by a fluctuation temperature, which changes from 18 K at 2 K to about 100 K at room temperature.

Ein Natrium-Oxocobaltat(II)-Sulfat: Na8[CoO3][SO4]2†

Na8[CoO3][SO4]2 wurde durch Redoxreaktion zwischen metallischem Cobalt und CdO in Anwesenheit von Na2SO4 und Na2O bei 550 °C (15 d) in Form roter Einkristalle erhalten. Die Kristallstruktur wurde anhand von Einkristalldaten bei 170 K bestimmt (IPDS-Daten, Cmcm, Z = 4, a = 806, 88(9) pm, b = 2232, 1(3) pm, c = 705, 97(9) pm, Rall = 0, 047). Uber die magnetischen Eigenschaften und spektroskopische Untersuchungen wird berichtet und die Ergebnisse im Rahmen des Angular-Overlap-Modells diskutiert. n n n nA Sodium Oxocobaltate(II) Sulfate: Na8[CoO3][SO4]2 n n n nNa8[CoO3][SO4]2 has been obtained from a redox reaction between cobalt metal and CdO in the presence of Na2SO4 and Na2O at 550 °C (15 d) as red single crystals. The structure has been determined from single crystal data (IPDS-data, T = 170 K, Cmcm, Z = 4, a = 806.88(9) pm, b = 2232.1(3) pm, c = 705.97(9) pm, Rall = 0.047). Magnetic properties and spectroscopic investigations are reported and discussed within the Angular-Overlap-Model.