16 research outputs found
Reduction of lattice thermal conductivity from planar faults in the layered Zintl compound SrZnSb_2
The layered Zintl compound SrZnSb_2 is investigated using transmission electron microscopy (TEM) to understand the low lattice thermal conductivity. The material displays out-of-phase boundaries with a spacing from 100 down to 2 nm. Density functional theory calculations confirm that the TEM-derived defect structure is energetically reasonable. The impact of these defects on phonon scattering is analyzed within the Debye–Callaway model, which reveals a significant reduction in the acoustic phonon mean free path. This enhancement in phonon scattering leads to an ~30% reduction in lattice thermal conductivity at 300 K
Enhancement of thermoelectric properties by energy filtering: Theoretical potential and experimental reality in nanostructured ZnSb
Energy filtering has been suggested by many authors as a means to improve
thermoelectric properties. The idea is to filter away low-energy charge
carriers in order to increase Seebeck coefficient without compromising
electronic conductivity. This concept was investigated in the present paper for
a specific material (ZnSb) by a combination of first-principles atomic-scale
calculations, Boltzmann transport theory, and experimental studies of the same
system. The potential of filtering in this material was first quantified, and
it was as an example found that the power factor could be enhanced by an order
of magnitude when the filter barrier height was 0.5~eV. Measured values of the
Hall carrier concentration in bulk ZnSb were then used to calibrate the
transport calculations, and nanostructured ZnSb with average grain size around
70~nm was processed to achieve filtering as suggested previously in the
literature. Various scattering mechanisms were employed in the transport
calculations and compared with the measured transport properties in
nanostructured ZnSb as a function of temperature. Reasonable correspondence
between theory and experiment could be achieved when a combination of constant
lifetime scattering and energy filtering with a 0.25~eV barrier was employed.
However, the difference between bulk and nanostructured samples was not
sufficient to justify the introduction of an energy filtering mechanism. The
reasons for this and possibilities to achieve filtering were discussed in the
paper
How to verify the precision of density-functional-theory implementations via reproducible and universal workflows
In the past decades many density-functional theory methods and codes adopting
periodic boundary conditions have been developed and are now extensively used
in condensed matter physics and materials science research. Only in 2016,
however, their precision (i.e., to which extent properties computed with
different codes agree among each other) was systematically assessed on
elemental crystals: a first crucial step to evaluate the reliability of such
computations. We discuss here general recommendations for verification studies
aiming at further testing precision and transferability of
density-functional-theory computational approaches and codes. We illustrate
such recommendations using a greatly expanded protocol covering the whole
periodic table from Z=1 to 96 and characterizing 10 prototypical cubic
compounds for each element: 4 unaries and 6 oxides, spanning a wide range of
coordination numbers and oxidation states. The primary outcome is a reference
dataset of 960 equations of state cross-checked between two all-electron codes,
then used to verify and improve nine pseudopotential-based approaches. Such
effort is facilitated by deploying AiiDA common workflows that perform
automatic input parameter selection, provide identical input/output interfaces
across codes, and ensure full reproducibility. Finally, we discuss the extent
to which the current results for total energies can be reused for different
goals (e.g., obtaining formation energies).Comment: Main text: 23 pages, 4 figures. Supplementary: 68 page
Charge-ordered spinel AlV<sub>2</sub>O<sub>4</sub>: High-energy-resolution EELS and computational studies
Experimental and theoretical study of electron density and structure factors in CoSb 3
a b s t r a c t We refine two low-order structure factors of the skutterudite CoSb 3 using convergent beam electron diffraction. The relatively large unit cell of this material causes the disks to overlap and introduces a series of challenges in the refinement procedure. These challenges and future work-arounds are discussed. The refined structure factors F 200 and F 600 are compared to X-ray diffraction and density functional calculated values, the latter calculated using two different functionals. Both relaxed and experimental lattice parameters are tested to explicitly highlight the impact of the lattice geometry and atomic position on the structure factors
Enhancement of thermoelectric properties by energy filtering: Theoretical potential and experimental reality in nanostructured ZnSb
Thermoelectric performance enhancement of (BiS)1.2(TiS2)2 misfit layer sulfide by chromium doping
The role of grain boundary scattering in reducing the thermal conductivity of polycrystalline XNiSn (X = Hf, Zr, Ti) half-Heusler alloys
How to verify the precision of density-functional-theory implementations via reproducible and universal workflows
In the past decades many density-functional theory methods and codes adopting periodic boundary conditions have been developed and are now extensively used in condensed matter physics and materials science research. Only in 2016, however, their precision (i.e., to which extent properties computed with different codes agree among each other) was systematically assessed on elemental crystals: a first crucial step to evaluate the reliability of such computations. We discuss here general recommendations for verification studies aiming at further testing precision and transferability of density-functional-theory computational approaches and codes. We illustrate such recommendations using a greatly expanded protocol covering the whole periodic table from Z=1 to 96 and characterizing 10 prototypical cubic compounds for each element: 4 unaries and 6 oxides, spanning a wide range of coordination numbers and oxidation states. The primary outcome is a reference dataset of 960 equations of state cross-checked between two all-electron codes, then used to verify and improve nine pseudopotential-based approaches. Such effort is facilitated by deploying AiiDA common workflows that perform automatic input parameter selection, provide identical input/output interfaces across codes, and ensure full reproducibility. Finally, we discuss the extent to which the current results for total energies can be reused for different goals (e.g., obtaining formation energies). This data entry contains all data to reproduce the results, as well as the resulting curated all-electron dataset and the scripts to generate the figures of the paper