Results for “Sr(ZnAs)2” | Engineering Papers

DOE OSTI2020

Materials Data on Sr(ZnAs)2 by Materials Project

Sr(ZnAs)2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Sr2+ is bonded to six equivalent As3- atoms to form SrAs6 octahedra that share corners with twelve equivalent ZnAs4 tetrahedra, edges with six equivalent SrAs6 octahedra, and edges with six equivalent ZnAs4 tetrahedra. All Sr–As bond lengths are 3.16 Å. Zn2+ is bonded to four equivalent As3- atoms to form ZnAs4 tetrahedra that share corners with six equivalent SrAs6 octahedra, corners with six equivalent ZnAs4 tetrahedra, edges with three equivalent SrAs6 octahedra, and edges with three equivalent ZnAs4 tetrahedra. The corner-sharing octahedra tilt angles range from 22–51°. There are three shorter (2.57 Å) and one longer (2.63 Å) Zn–As bond lengths. As3- is bonded to three equivalent Sr2+ and four equivalent Zn2+ atoms to form a mixture of distorted corner and edge-sharing AsSr3Zn4 pentagonal bipyramids.

36 MATERIALS SCIENCE↗

DOE OSTI2022

On the Effects of Aliovalent Substitutions in Thermoelectric Zintl Pnictides. Varied Polyanionic Dimensionality and Complex Structural Transformations–The Case of Sr 3 ZnP 3 vs Sr 3 Al x Zn 1– x P 3

The structures and the transport properties of a novel family of Zintl phosphides and arsenides with the formula AE 3 ZnPn 3 and the solid solutions AE 3 Al x Zn 1–x Pn 3 , AE 3 ZnAs y P 1–y (AE = Sr, Eu; Pn = P, As) are reported. Crystals of nine new phases have been obtained via Pb-flux reactions and used for structural work by means of single-crystal X-ray diffraction methods. The derived orthorhombic structure is without a direct analog, and features unusual structural units, where the Zn atoms are in both distorted tetrahedral and trigonal-planar coordination of pnictogens. Electronic structure calculations reveal moderately wide bandgaps for Sr 3 ZnP 3 and Sr 3 ZnAs 3 , on the order of 0.70 and 0.63 eV, respectively. Electrical transport measurements above room temperature indicate relatively high resistivity values above 500 K (ρ ≈ 4.8 Ω cm and above), but some of the samples exhibit very high Seebeck coefficients, as large as 300 μV/K at 560 K for Sr 3 ZnAs 3 . Aliovalent substitutions in AE 3 ZnPn 3 , achieved by the partial replacement of Zn 2+ with Al 3+ cations promote occupational and positional disorder, which causes structural transformation towards the disordered variant of the Sr 5 Al 2 Sb 6 structure type. Such substitutions also change the dimensionality of the polyanionic sub-lattice in the resulting quaternary AE 3 Al x Zn 1–x Pn 3 phases. Furthermore, preliminary transport property data on the latter reveal nine times lower electrical resistivity (ρ 500 ≈ 0.5 Ω cm) together with a significantly enhanced Seebeck coefficient, αmax ≈ 430 μV/K at 560 K.

36 MATERIALS SCIENCE↗