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13 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Structural Complexity and Tuned Thermoelectric Properties of a Polymorph of the Zintl Phase Ca 2 CdSb 2 with a Non-centrosymmetric Monoclinic Structure

The Zintl phase Ca 2 CdSb 2 was found to be dimorphic. Besides the orthorhombic Ca 2 CdSb 2 (-o), here we report on the synthesis, the structural characterization, and the thermoelectric transport properties of its monoclinic form, Ca 2 CdSb 2 (-m), and its Lu-doped variant Ca 2–x Lu x CdSb 2 (x ≈ 0.02). The monoclinic structure exhibits complex structural characteristics and constitutes a new structure type with the non-centrosymmetric space group Cm (Z = 30). The electrical resistivity ρ(T) measured on single crystals of both phases portrays a transition from a semiconductor to a degenerate p-type semiconductor upon doping with Lu and with an attendant change in the Hall carrier concentration nH from 7.15 × 10 18 to 2.30 × 10 19 cm –3 at 300 K. The Seebeck coefficient S(T) of both phases are comparable and indicate a hole-dominated carrier transport mechanism with magnitudes of 133 and 116 μV/K at 600 K for Ca 2 CdSb 2 (-m) and Ca 2–x Lu x CdSb 2 , respectively. The convoluted atomic bonding with an attendant large unit cell volume of ~4365 Å 3 drives a putative low thermal conductivity in these materials resulting in a power factor PF of 1.63 μW/cm K 2 and an estimated thermoelectric figure of merit zT of ~0.5 for Ca 2–x Lu x CdSb 2 at 600 K. Furthermore, differential scanning calorimetry results reveal the stability of these phases up to about 960 K, making them candidates for moderate temperature thermoelectric materials.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CdSb by Materials Project

CdSb is SC16 CuCl, stable at 5GPa structured and crystallizes in the orthorhombic Pbca space group. The structure is three-dimensional. Cd2+ is bonded to four equivalent Sb2- atoms to form a mixture of corner and edge-sharing CdSb4 tetrahedra. There are a spread of Cd–Sb bond distances ranging from 2.86–3.16 Å. Sb2- is bonded in a 5-coordinate geometry to four equivalent Cd2+ and one Sb2- atom. The Sb–Sb bond length is 2.86 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Tl2(CdSb)3 by Materials Project

Tl2(CdSb)3 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are three inequivalent Cd2+ sites. In the first Cd2+ site, Cd2+ is bonded to four Sb+2.67- atoms to form a mixture of distorted edge and corner-sharing CdSb4 tetrahedra. There are a spread of Cd–Sb bond distances ranging from 2.89–3.23 Å. In the second Cd2+ site, Cd2+ is bonded to two equivalent Tl1+ and four Sb+2.67- atoms to form a mixture of distorted edge and corner-sharing CdTl2Sb4 tetrahedra. Both Cd–Tl bond lengths are 3.36 Å. There are a spread of Cd–Sb bond distances ranging from 2.91–3.00 Å. In the third Cd2+ site, Cd2+ is bonded to four Sb+2.67- atoms to form corner-sharing CdSb4 tetrahedra. There are a spread of Cd–Sb bond distances ranging from 2.91–3.02 Å. There are two inequivalent Tl1+ sites. In the first Tl1+ site, Tl1+ is bonded in a 6-coordinate geometry to two equivalent Cd2+, two equivalent Tl1+, and two equivalent Sb+2.67- atoms. Both Tl–Tl bond lengths are 3.73 Å. Both Tl–Sb bond lengths are 3.51 Å. In the second Tl1+ site, Tl1+ is bonded in a 3-coordinate geometry to three Sb+2.67- atoms. There are two shorter (3.43 Å) and one longer (3.51 Å) Tl–Sb bond lengths. There are three inequivalent Sb+2.67- sites. In the first Sb+2.67- site, Sb+2.67- is bonded in a 4-coordinate geometry to four Cd2+ and three Tl1+ atoms. In the second Sb+2.67- site, Sb+2.67- is bonded in a 7-coordinate geometry to five Cd2+ and two equivalent Tl1+ atoms. In the third Sb+2.67- site, Sb+2.67- is bonded in a 4-coordinate geometry to three Cd2+ and one Sb+2.67- atom. The Sb–Sb bond length is 2.87 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(CdSb)2 by Materials Project

Sr(CdSb)2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Sr2+ is bonded to six equivalent Sb3- atoms to form SrSb6 octahedra that share corners with twelve equivalent CdSb4 tetrahedra, edges with six equivalent SrSb6 octahedra, and edges with six equivalent CdSb4 tetrahedra. All Sr–Sb bond lengths are 3.40 Å. Cd2+ is bonded to four equivalent Sb3- atoms to form CdSb4 tetrahedra that share corners with six equivalent SrSb6 octahedra, corners with six equivalent CdSb4 tetrahedra, edges with three equivalent SrSb6 octahedra, and edges with three equivalent CdSb4 tetrahedra. The corner-sharing octahedra tilt angles range from 17–55°. There are three shorter (2.92 Å) and one longer (3.02 Å) Cd–Sb bond lengths. Sb3- is bonded to three equivalent Sr2+ and four equivalent Cd2+ atoms to form a mixture of distorted edge and corner-sharing SbSr3Cd4 pentagonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CdSb by Materials Project

CdSb is High Pressure Cadmuum Telluride structured and crystallizes in the orthorhombic Pmmm space group. The structure is three-dimensional. Cd2+ is bonded in a distorted rectangular see-saw-like geometry to four equivalent Sb2- atoms. All Cd–Sb bond lengths are 3.18 Å. Sb2- is bonded to four equivalent Cd2+ and four equivalent Sb2- atoms to form a mixture of distorted edge and corner-sharing SbCd4Sb4 hexagonal bipyramids. There are two shorter (3.11 Å) and two longer (3.24 Å) Sb–Sb bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Eu(CdSb)2 by Materials Project

EuCd2Sb2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Eu2+ is bonded to six equivalent Sb3- atoms to form EuSb6 octahedra that share corners with twelve equivalent CdSb4 tetrahedra, edges with six equivalent EuSb6 octahedra, and edges with six equivalent CdSb4 tetrahedra. All Eu–Sb bond lengths are 3.33 Å. Cd2+ is bonded to four equivalent Sb3- atoms to form CdSb4 tetrahedra that share corners with six equivalent EuSb6 octahedra, corners with six equivalent CdSb4 tetrahedra, edges with three equivalent EuSb6 octahedra, and edges with three equivalent CdSb4 tetrahedra. The corner-sharing octahedra tilt angles range from 15–56°. There are three shorter (2.91 Å) and one longer (3.00 Å) Cd–Sb bond lengths. Sb3- is bonded to three equivalent Eu2+ and four equivalent Cd2+ atoms to form a mixture of distorted edge and corner-sharing SbEu3Cd4 pentagonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(CdSb)2 by Materials Project

CaCd2Sb2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Ca2+ is bonded to six equivalent Sb3- atoms to form CaSb6 octahedra that share corners with twelve equivalent CdSb4 tetrahedra, edges with six equivalent CaSb6 octahedra, and edges with six equivalent CdSb4 tetrahedra. All Ca–Sb bond lengths are 3.27 Å. Cd2+ is bonded to four equivalent Sb3- atoms to form CdSb4 tetrahedra that share corners with six equivalent CaSb6 octahedra, corners with six equivalent CdSb4 tetrahedra, edges with three equivalent CaSb6 octahedra, and edges with three equivalent CdSb4 tetrahedra. The corner-sharing octahedra tilt angles range from 13–57°. There are three shorter (2.92 Å) and one longer (3.02 Å) Cd–Sb bond lengths. Sb3- is bonded to three equivalent Ca2+ and four equivalent Cd2+ atoms to form a mixture of distorted edge and corner-sharing SbCa3Cd4 pentagonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Yb(CdSb)2 by Materials Project

YbCd2Sb2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Yb2+ is bonded to six equivalent Sb3- atoms to form YbSb6 octahedra that share corners with twelve equivalent CdSb4 tetrahedra, edges with six equivalent YbSb6 octahedra, and edges with six equivalent CdSb4 tetrahedra. All Yb–Sb bond lengths are 3.25 Å. Cd2+ is bonded to four equivalent Sb3- atoms to form CdSb4 tetrahedra that share corners with six equivalent YbSb6 octahedra, corners with six equivalent CdSb4 tetrahedra, edges with three equivalent YbSb6 octahedra, and edges with three equivalent CdSb4 tetrahedra. The corner-sharing octahedra tilt angles range from 13–57°. There are three shorter (2.91 Å) and one longer (3.03 Å) Cd–Sb bond lengths. Sb3- is bonded to three equivalent Yb2+ and four equivalent Cd2+ atoms to form a mixture of distorted corner and edge-sharing SbYb3Cd4 pentagonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Observation of Anomalously High Seebeck Coefficients in the Family of Zintl Phase Semiconductors Ca 10 RE CdSb 9 ( RE = Rare-Earth Metal)

This work reports the synthesis, structure and thermoelectric transport properties of the hole-dominated semiconductors with a general formula Ca 10 RECdSb 9 (RE = Y, Ce, Nd, Sm, and Lu). These materials feature unexpectedly high Seebeck coeffi-cients, up to 650 µV/K at 600 K, and electrical resistivities on the order of 1–1000 mΩ·cm, which is an indication of a degen-erate semiconducting state. For example, the Seebeck coeffi-cient observed in Ca 10 NdCdSb 9 (309 µV/K at 600 K) is accom-panied by low and metallic-like electrical resistivity (6 mΩ·cm) and a carrier concentration n = 4.68×10 20 cm –3 . The calculated power factor PF in Ca 10 NdCdSb 9 is 0.88 µW/cm·K 2 at 300 K, and calculations based on the single parabolic band model indi-cate that an optimum PF opt of 1.68 μW/cm·K 2 can be achieved at that temperature for a carrier concentration n opt = 6.62 × 10 19 cm –3 . Here, the estimated thermoelectric figure of merit zT in this material, when properly tuned is expected to surpass zT = 1 at 600 K.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Interface atomic structures in a cadmium arsenide/III–V semiconductor heterostructure

The interface atomic structure between an epitaxial thin film of the prototype topological semimetal cadmium arsenide (Cd 3 As 2 ) and a III–V semiconductor layer is investigated using high-angle annular dark-field imaging in an aberration-corrected scanning transmission electron microscope. We find that the interface unit cell adopts a defined stoichiometry that is CdSb-like, which is achieved through the insertion of periodically arranged Cd vacancies in the terminating Cd-plane of Cd 3 As 2 . This interface stoichiometry is consistent with the Sb-termination of the III–V layer and the fact that CdSb is the thermodynamically stable phase in the Cd–Sb binary system. We find at least two distinct alignments of the film with respect to the buffer layer, which are characterized by a $\frac{1}{4}$ <100> Cd 3 As 2 shift parallel to the interface. We show that steps of half unit cell height in the III–V layer can produce these distinct interface structures.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Materials Data on CdCuSb by Materials Project

CuCdSb is half-Heusler structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional and consists of four copper molecules and one CdSb framework. In the CdSb framework, Cd2+ is bonded to four equivalent Sb3- atoms to form corner-sharing CdSb4 tetrahedra. All Cd–Sb bond lengths are 2.84 Å. Sb3- is bonded to four equivalent Cd2+ atoms to form distorted corner-sharing SbCd4 tetrahedra.

36 MATERIALS SCIENCE↗