Physical properties of {Ti,Zr,Hf}₂Ni₂Sn compounds

Author(s)

V. V. Romaka, Gerda Rogl, Vilma Bursikova, Jiří Buršík, Herwig Michor, Andriy Grytsiv, E. Bauer, Gerald Giester, Peter Franz Rogl

Abstract

Physical properties, i.e. electrical resistivity (4.2–800 K), Seebeck coefficient (300–800 K), specific heat (2–110 K), Vickers hardness and elastic moduli (RT), have been defined for single-phase compounds with slightly nonstoichiometric compositions: Ti2.13Ni2Sn0.87, Zr2.025Ni2Sn0.975, and Hf2.055Ni2Sn0.945. From X-ray single crystal and TEM analyses, Ti2+xNi2Sn1−x, x ∼ 0.13(1), is isotypic with the U2Pt2Sn-type (space group P42/mnm, ternary ordered version of the Zr3Al2-type), also adopted by the homologous compounds with Zr and Hf. For all three polycrystalline compounds (relative densities >95%) the electrical resistivity of the samples is metallic-like with dominant scattering from static defects mainly conditioned by off-stoichiometry. Analyses of the specific heat curves Cpvs. T and Cp/T vs. T2 reveal Sommerfeld coefficients of γTi2Ni2Sn = 14.3(3) mJ mol−1 K−2, γZr2Ni2Sn = 10(1) mJ mol−1 K−2, γHf2Ni2Sn = 9.1(5) mJ mol−1 K−2 and low-temperature Debye-temperatures: θLTD = 373(7)K, 357(14)K and 318(10)K. Einstein temperatures were in the range of 130–155 K. Rather low Seebeck coefficients (<15 μV K−1), power factors (pf < 0.07 mW mK−2) and an estimated thermal conductivity of λ < 148 mW cm−1 K−1 yield thermoelectric figures of merit ZT < 0.007 at ∼800 K. Whereas for polycrystalline Zr2Ni2Sn elastic properties were determined by resonant ultrasound spectroscopy (RUS): E = 171 GPa, ν = 0.31, G = 65.5 GPa, and B = 147 GPa, the accelerated mechanical property mapping (XPM) mode was used to map the hardness and elastic moduli of T2Ni2Sn. Above 180 K, Zr2Ni2Sn reveals a quasi-linear expansion with CTE = 15.4 × 10−6 K−1. The calculated density of states is similar for all three compounds and confirms a metallic type of conductivity. The isosurface of elf shows a spherical shape for Ti/Zr/Hf atoms and indicates their ionic character, while the [Ni2Sn]n− sublattice reflects localizations around the Ni and Sn atoms with a large somewhat diffuse charge density between the closest Ni atoms.

Organisation(s)

Department of Materials Chemistry, Department of Mineralogy and Crystallography

External organisation(s)

Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden, Masaryk University, Czech Academy of Sciences, Technische Universität Wien

Journal

Dalton Transactions

Volume

51

Pages

361-374

No. of pages

14

ISSN

1477-9226

DOI

https://doi.org/10.1039/d1dt03198h

Publication date

2022

Peer reviewed

Yes

Austrian Fields of Science 2012

104021 Structural chemistry, 105113 Crystallography, 103018 Materials physics

Keywords

ASJC Scopus subject areas

Inorganic Chemistry

Portal url

https://ucrisportal.univie.ac.at/en/publications/103aa105-5d15-4599-ad33-462443ec09f9