Basing on the ab initio calculations performed within full potential local orbital minimum basis method, the Mulliken occupation of the Sr 5s (n_{5s}) and Ba 6p (n_{6p}) states can serve as an indicator of transition to the superconducting state in doped SrFe₂As₂ and BaFe₂As₂ compounds where the iron was substituted with cobalt or in the pristine compounds under pressure. The estimated pressure, at which both compounds exhibit superconductivity based on Sr 5s and Ba 6p occupation is in good agreement with the recently published experimental data.
Full potential linearized augmented plane wave band structure calculations were performed for hexagonal RENi_5 (RE = rare earth) compounds in order to investigate reproducibility of lanthanide contraction by ab initio studies. The a and c parameters were optimised using a paraboloid fit, starting from the same initial values for all compounds studied. The trend in lattice parameters across the RE series obtained from the calculations was found to be in general agreement with experimental data. A comparison of results obtained by generalized gradient approximation and generalized gradient approximation with additional Coulomb correlations calculations is presented for several double counting schemes.
We measured thermopower, thermal conductivity and electrical resitivity for Ca₂Sn sample across 4-350 K temperature range. Contrary to expectations from recent DFT based calculations the thermopower is not particularly large, reaching 7 μV at 350 K. The thermoelectric figure of merit renders this material in unmodified form practically unusable for thermoelectric aplications.
Electronic structure of a ternary TmPdIn compound, which crystallizes in the hexagonal ZrNiAl-type structure, was studied by X-ray photoemission spectroscopy and ultraviolet photoemission spectroscopy. Density of states in the valence band was calculated by means of the augmented plane wave/local orbital method based on density functional theory. The results showed that the valence band is formed mainly of Tm 4f and Pd 4d states. In the ultraviolet photoemission spectra one can distinguish Pd 4d maximum and Tm 4f multiplet peaks, which are displaced with respect to those of pure Tm.
The heavy fermion compound Ce₃Co₄Sn₁₃ was studied in terms of its thermoelectric properties. To enhance its figure of merit we milled the solid sample and then pressed to obtain a consistent granulated material. The main properties, such as the Seebeck coefficient, thermal conductivity and electronic resistivity were measured at low (< 300 K) temperatures for both, the solid and the granulated sample. Thermal conductivity was diminished and the Seebeck coefficient was slightly enhanced, while the resistivity of produced material was increased. We explain it by strong electron scattering on defects and grain boundaries present in the sample. The resulting figure of merit ZT was found to be enhanced almost across the whole measured T region.
An antiferromagnetic order with a Néel temperature T_{N} = 17.5 K, a strong ferromagnetic exchange evidenced by a positive Curie-Weiss temperature θ_{CW} = 77.3 K, the fuzzy peaks in the real component of susceptibility χ'(T) and the disappearance of the second critical field were established. The curvature of specific heat C(T) and C(T)/T in surrounding of T_{N} indicated a broad peak, characteristic for the system with inhomogeneous magnetic state (spin-glass-like phase). The calculated magnetic entropy showed the value of S(T) ≈ 1 J/(mol K) which is extremely small; i.e., much lower than the magnetic contribution Rln(2S + 1) = 11.52 J/(mol K) calculated for the spin 3/2.
This work presents studies of the valence band of two Kondo lattice systems: Ce_2Co_{0.8}Si_{3.2}, which is paramagnetic with the Kondo temperature T_{K} ≈50 K and Ce_2RhSi_3, which is antiferromagnetic below T_{N}=4.5 K and exhibits T_{K} ≈9 K. The photoemission spectra, which are obtained with photon energy tuned to Ce 4d-4f resonance, reveal a Kondo peak at the Fermi energy (E_{F}), its spin-orbit splitting partner at 0.24 eV and a broad maximum related to Ce f^0 final state. The spectra indicate that Kondo peak has a higher intensity for Ce_2Co_{0.8}Si_{3.2}. The off-resonance photoemission data reveal that a maximum in the 3d electron density of states is shifted towards E_{F} for Ce_2Co_{0.8}Si_{3.2} as compared to Ce_2RhSi_3. Full-potential local-orbital calculations were realized with local spin density approach +U approach for 213 stoichiometry. They show that a higher density of states near E_{F} is observed for Ce_2CoSi_3. The calculations also reveal the existing tendencies for antiferromagnetic and ferromagnetic ground states in a case of Ce_2RhSi_3 and Ce_2CoSi_3, respectively.
JavaScript is turned off in your web browser. Turn it on to take full advantage of this site, then refresh the page.