17 research outputs found
Mulliken occupation as the indicator of transition to superconducting state in SrFe2As2 and BaFe2As2
Basing on the ab initio calculations performed within full potential local orbital minimum basis method, the
Mulliken occupation of the Sr 5s (n5s) and Ba 6p (n6p) 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
Lanthanide Contraction in RENi 5 (RE = La, Ce, Nd, Sm, Eu, Gd, Tb, Yb) compounds studied with band structure calculations
Full potential linearized augmented plane wave band structure calculations were performed for hexagonal
RENi5 (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 t, 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
“DistorX” program for analysis of structural distortions affecting X-ray diffraction patterns
For the purposes of research on strongly correlated electronic systems (SCES), a computer
program, DistorX (Distortion or X-ray diffraction patterns), was created. The
program is an interactive Jupyter notebook for simulating the effects of structural distortions
on X-ray diffraction patterns. The program is designed to be universal, in that
it may be successfully applied to a variety of structures. In previous reports, a structural
transition from a cubic phase of Yb3Rh4Sn13 – type to the superlattice variantwas been
observed at 160 K for a series of skutterudite-related Ce3M4Sn13 compounds, where
M = Co, Ru or Rh. In this work, we use a specialized build of DistorX to simulate
the low-temperature X-ray diffraction patterns of a distorted unit cell. The
method described here obtains simulated XRD patterns from the atomic positions
and permits investigation of crystal structure without imposed symmetry operations.
We further indicate the crystallographic plane in which the distortion occurs,
and explain the possible origin of CDW in these materials
Thermoelectric properties of Ca2Sn/Ca3SnO
This type of materials was first synthesized in 1961
(Eckerlin), and its structure was determined by XRD
measurements [1]. There are little experimental studies
of thermodynamic and electrical properties of these
compounds [2–4], as even in the first paper it was observed
that these materials within a very short time
turn into black powder after exposure to air. That
powder contains mainly oxidation products. Recently,
these materials were studied using ab-initio calculations
and they were predicted to possess very promising thermopower
[5–10]. Its real crystal structure is also a matter
of debate [3, 8, 9]. The usability of thermoelectric material
for thermoelectric applications depend on figure of
merit, where high thermopower, small thermal conductivity
and low resistivity is expected from a prospective
material [11, 12]. Due to recent ab-initio studies we decided
to revisit Ca2Sn, and measure its thermoelectric
properties[…
Studies of electronic structure across a quantum phase transition in CeRhSb_{1-x}Sn_{x}
We study an electronic structure of CeRhSb1xSnx system, which displays quantum critical
transition from a Kondo insulator to a non-Fermi liquid at x = 0:13. We provide ultraviolet photoelectron
spectra of valence band obtained at 12.5 K. A coherent peak at the Fermi level is not present in the data,
but a signal related to 4f1
7=2 nal state is detected. Spectral intensity at the Fermi edge has a general
tendency to grow with Sn content. Theoretical calculations of band structure are realized with full-potential
local-orbital minimum-basis code using scalar relativistic and full relativistic approach. The calculations
reveal a depletion of density of states at the Fermi level for CeRhSb. This gap is shifted above the Fermi
energy with increasing Sn content and thus a rise of density of states at the Fermi level is re
ected in
the calculations. It agrees with metallic properties of compounds with larger x. The calculations also yield
another important e ect of Sn substitution. Band structure is displaced in a direction corresponding to hole
doping, although with deviations from a rigid band shift scenario. Lifshitz transitions modify a topology
of the Fermi surface a few times and a number of bands crossing the Fermi level increases
Thermoelectric properties of heavy fermion compound Ce3Co4Sn13
The heavy fermion compound Ce3Co4Sn13 was studied in terms of its thermoelectric properties. To enhance
its gure of merit we milled the solid sample and then pressed to obtain a consistent granulated material. The main properties, such as the Seebeck coe cient, 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 coe cient 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 gure of merit ZT was found to be enhanced almost across the whole measured T region
Electronic structure of TmPdIn
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
Specific heat and magnetic properties of single-crystalline (Zn0.925In0.054)[Cr1.84In0.152]Se-4 semiconductor
An antiferromagnetic order with a Néel temperature TN = 17:5 K, a strong ferromagnetic exchange evidenced
by a positive Curie Weiss temperature CW = 77:3 K, the fuzzy peaks in the real component of susceptibility x′
(T) and the disappearance of the second critical eld were established. The curvature of speci c heat C(T) and
C(T)=T in surrounding of TN 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
Valence band of and studied by resonant photoemission spectroscopy and FPLO calculations
This work presents studies of the valence band of two Kondo lattice systems: Ce2Co0.8Si3.2, which is paramagnetic with the Kondo temperature T-K approximate to 50 K and Ce2RhSi3, which is antiferromagnetic below T-N = 4.5 K and exhibits TK approximate to 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 Ce2Co0.8Si3.2. The off-resonance photoemission data reveal that a maximum in the 3d electron density of states is shifted towards EF for Ce2Co0.8Si3.2 as compared to Ce2RhSi3. 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 EF is observed for Ce2CoSi3. The calculations also reveal the existing tendencies for antiferromagnetic and ferromagnetic ground states in a case of Ce2RhSi3 and Ce2CoSi3, respectively
Dipole Relaxation in Semiconducting Zn2−xMgxInV3O11 Materials (Where x = 0.0, 0.4, 1.0, 1.6, and 2.0)
This paper reports on the electrical and broadband dielectric spectroscopy studies of
Zn2xMgxInV3O11 materials (where x = 0.0, 0.4, 1.0, 1.6, 2.0) synthesized using a solid-state
reaction method. These studies showed n-type semiconducting properties with activation energies
of 0.147–0.52 eV in the temperature range of 250–400 K, symmetric and linear I–V characteristics,
both at 300 and 400 K, with a stronger carrier emission for the matrix and much less for the remaining
samples, as well as the dipole relaxation, which was the slowest for the sample with x = 0.0 (matrix)
and was faster for Mg-doped samples with x > 0.0. The faster the dipole relaxation, the greater
the accumulation of electric charge. These e ects were analyzed within a framework of the DC
conductivity and the Cole–Cole fit function, including the solid-state density and porosity of the
sample. The resistivity vs. temperature dependence was well fitted using the parallel resistor model.
Our ab initio calculations also show that the bandgap increased with the Mg content