Physical properties of {Ti,Zr,Hf}(2)Ni2Sn compounds
| Authors | |
|---|---|
| Year of publication | 2022 |
| Type | Article in Periodical |
| Magazine / Source | Dalton Transactions |
| MU Faculty or unit | |
| Citation | |
| web | https://pubs.rsc.org/en/content/articlehtml/2022/dt/d1dt03198h |
| Doi | http://dx.doi.org/10.1039/d1dt03198h |
| Keywords | TI-NI-SN; MECHANICAL-PROPERTIES; CRYSTAL-STRUCTURE; PHASE-EQUILIBRIA; THERMAL-EXPANSION; SYSTEM; CONSTITUTION; HF2NI2SN |
| Description | 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 ?Ti2Ni2Sn = 14.3(3) mJ mol-1 K-2, ?Zr2Ni2Sn = 10(1) mJ mol-1 K-2, ?Hf2Ni2Sn = 9.1(5) mJ mol-1 K-2 and low-temperature Debye-temperatures: ?LTD = 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 ? < 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, ? = 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. |
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