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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

High-pressure effects on isotropic superconductivity in the iron-free layered pnictide superconductor BaPd 2 As 2

While the layered 122 iron arsenide superconductors are highly anisotropic, unconventional, and exhibit several forms of electronic orders that coexist or compete with superconductivity in different regions of their phase diagrams, we find in the absence of iron in the structure that the superconducting characteristics of the end member BaPd 2 As 2 are surprisingly conventional. Here we report on complementary measurements of specific heat, magnetic susceptibility, resistivity measurements, Andreev spectroscopy, and synchrotron high pressure x-ray diffraction measurements supplemented with theoretical calculations for BaPd 2 As 2 . Its superconducting properties are completely isotropic as demonstrated by the critical fields, which do not depend on the direction of the applied field. Under the application of high pressure, T c is linearly suppressed, which is the typical behavior of classical phonon-mediated superconductors with some additional effect of a pressure-induced decrease in the electronic density of states and the electron-phonon coupling parameters. Structural changes in the layered BaPd 2 As 2 have been studied by means of angle-dispersive diffraction in a diamond-anvil cell. At 12 GPa and 24.2 GPa we observed pressure induced lattice distortions manifesting as the discontinuity and, hence discontinuity in the Birch-Murnaghan equation of state. The bulk modulus is B 0 = 40 (6) GPa below 12 GPa and B 0 = 142 (3) GPa below 27.2 GPa.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Remarkable thermoelectric performance in BaPdS 2 via pudding-mold band structure, band convergence, and ultralow lattice thermal conductivity

Efficient thermoelectric materials require a rare and contraindicated combination of materials properties: large electrical conductivity, large Seebeck coefficient, and low thermal conductivity. One strategy to achieve the first two properties is via low-energy electronic bands containing both flat and dispersive parts in different regions of crystal momentum space, known as a pudding-mold band structure. Here, we illustrate that BaPdS 2 successfully achieves the pudding-mold band structure for the valence band, contributing to a large p-type thermoelectric power factor, due to its anisotropic crystal structure containing zigzag chains of edge-sharing square planar PdS 4 units; large power factor is achieved for n-type doping as well due to band convergence. In addition, BaPdS 2 exhibits ultralow lattice thermal conductivity, and thus also achieves the third property, due to extremely soft and anharmonic interactions in its transverse acoustic phonon branch. We predict a remarkably large thermoelectric figure of merit, with peak values between 2 and 3 for two of the three crystallographic directions, suggesting BaPdS 2 warrants experimental investigation.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Materials Data on BaPd by Materials Project

BaPd crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. Ba is bonded in a 7-coordinate geometry to seven equivalent Pd atoms. There are six shorter (3.35 Å) and one longer (3.54 Å) Ba–Pd bond lengths. Pd is bonded in a 9-coordinate geometry to seven equivalent Ba and two equivalent Pd atoms. Both Pd–Pd bond lengths are 2.91 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BaPd by Materials Project

BaPd crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ba is bonded in a 6-coordinate geometry to six equivalent Pd atoms. All Ba–Pd bond lengths are 3.28 Å. Pd is bonded in a distorted body-centered cubic geometry to six equivalent Ba and two equivalent Pd atoms. Both Pd–Pd bond lengths are 2.83 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BaPd(SeO3)2 by Materials Project

BaPd(SeO3)2 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Ba2+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ba–O bond distances ranging from 2.76–3.07 Å. Pd2+ is bonded in a square co-planar geometry to four O2- atoms. There are two shorter (2.03 Å) and two longer (2.05 Å) Pd–O bond lengths. Se4+ is bonded in a distorted trigonal non-coplanar geometry to three O2- atoms. There are a spread of Se–O bond distances ranging from 1.70–1.77 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ba2+ and one Se4+ atom. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ba2+, one Pd2+, and one Se4+ atom. In the third O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ba2+, one Pd2+, and one Se4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Physical properties investigation of tetragonal Ba T 2 P 2 (T = Ru, Pd)

The structural, thermal, electrical transport, and magnetic properties of ternary compounds BaT 2 P 2 (T = Ru, Pd) are reported together with electronic structure calculations. Our results show that BaRu 2 P 2 crystallises in the layered tetragonal ThCr 2 Si 2 -type structure (space group I4/mmm) whereas BaPd 2 P 2 adopts the primitive tetragonal CeMg 2 Si 2 -type structure (space group P4/mmm). The combined experimental results and electronic structure calculations suggest metallic and diamagnetic ground states for both materials. Electrical transport measurements further indicate non-Fermi liquid behaviour at low temperatures. Notably, BaRu 2 P 2 exhibits an anomalous feature in the magnetic susceptibility at T ~ 260 K, similar to that observed in BaRu 2 As 2 . A comparison between the bare density of states obtained from electronic structure calculations and the experimentally estimated values suggests the presence of strong correlation effects in the material. Furthermore, the heat capacity of BaPd 2 P 2 , calculated using the full phonon dispersion relation, is in good agreement with the experimental data, particularly at low temperatures, highlighting the significant contribution of optical phonon branches to C P in this temperature range.

flat bands↗