Thermoelectric materials transform a thermal gradient into electricity. The efficiency of this process relies on three material-dependent parameters: the Seebeck coefficient, the electrical resistivity and the thermal conductivity, summarized in the thermoelectric figure of merit. A large figure of merit is beneficial for potential applications such as thermoelectric generators. Here we report the thermal and electronic properties of thin-film Heusler alloys based on Fe2V0.8W0.2Al prepared by magnetron sputtering. Density functional theory calculations suggest that the thin films are metastable states, and measurements of the power factor—the ratio of the Seebeck coefficient squared divided by the electrical resistivity—suggest a high intrinsic figure of merit for these thin films. This may arise from a large differential density of states at the Fermi level and a Weyl-like electron dispersion close to the Fermi level, which indicates a high mobility of charge carriers owing to linear crossing in the electronic bands.
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The data that support the findings of this study are available from the corresponding author upon reasonable request.
The computer codes that support the findings of this study are available from the corresponding author upon reasonable request.
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This research is supported by the Christian Doppler Laboratory for Thermoelectricity and the JST, CREST (grant numbers JPMJCR15Q6 and JPMJCR19Q4). Work at IMR, China, was supported by the National Science Fund for Distinguished Young Scholars (grant number 51725103), by the National Natural Science Foundation of China (grant number 51671193), by the Science Challenging Project (grant number TZ2016004), and by the Shanghai Nuclear Engineering Research & Design Institute (major research project 2018ZX06002004).
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Peer review information Nature thanks Stephen R. Boona and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Extended data figures and tables
a, ELNES of the oxygen K-edge of the thin alumina interlayer at 532-eV energy loss and the vanadium L-edge at 513-eV energy loss of the Heusler alloy. b, ELNES of the iron L-edge in Fe2Si and the Heusler alloy.
The thin film, the interface and the Si substrate are shown. ΔT is the temperature difference between the electrodes, denoted as U+ and U−.
Extended Data Fig. 3 Electronic and thermoelectric transport of the composite (Heusler film, interface and Si substrate) and of the isolated Si substrate.
a, Temperature-dependent Seebeck coefficient S. b, Temperature-dependent electrical resistivity ρ.
a, Field-dependent Hall resistivity ρxy at various temperatures. The solid lines are least-squares fits, as explained in Methods. b, Temperature-dependent charge carrier densities n and mobilities μ, derived from the above least-squares fits. Circle and triangle symbols indicate the data for the majority and minority electrons, respectively; the coloured and open symbols indicate the data for charge carrier density and mobility, respectively. The dashed lines are guides to the eye.
Extended Data Fig. 5 Field-dependent Hall resistivity ρxy of bulk Fe2V0.8W0.2Al at T = 380 K and T = 300 K.
The solid lines are least-squares fits, as explained in Methods.
Extended Data Fig. 6 Temperature-dependent transport and thermoelectric properties of thin-film Fe2V0.8W0.2Al.
Data are taken over four runs, each for increasing and decreasing temperatures. a, Temperature-dependent Seebeck coefficient S. b, Temperature-dependent electrical resistivity ρ. c, Temperature-dependent power factor PF.
Extended Data Fig. 7 Thermoreflectance signal of thin film Fe2V0.8W0.2Al with deposited 100-nm-thick Al surface layer.
The data are observed by the picosecond thermoreflectance method. a, The signal data are enlarged around the instant of pump laser irradiation at t = 0 with the fitting curve calculated using the mirror image method. b, The entire signal from pulse to pulse. c, The signal enlarged around the pump laser irradiation using the method reported in refs. 54,55. The red dotted lines in b and c are corrected signals for single-pulse heating. The blue solid lines are least-squares fits as explained in Methods.
Extended Data Fig. 8 Thermoreflectance signal of the 680-nm-thick TiN reference film deposited on a quartz substrate.
The signal was obtained using the ultrafast laser flash method.
a, Parent material Fe2VAl. b, Parent material Fe2V0.8W0.2Al. Descriptions and interpretations are summarized in Methods.
a, b, Electron dispersion along the high-symmetry directions of the bcc structure around the Fermi level for spin-up (a) and spin-down bands (b). The dispersion of Fe2VAl is illustrated by black solid lines; the coloured lines refer to Fe2V0.8W0.2Al. c–e, Fermi surfaces of bcc Fe2V0.8W0.2Al at 0.11 eV above the Fermi level on Z–R (c); on R–A (d); and at 0.13 eV above the Fermi level on Γ–R (e). Descriptions and interpretations are summarized in Methods.
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Hinterleitner, B., Knapp, I., Poneder, M. et al. Thermoelectric performance of a metastable thin-film Heusler alloy. Nature 576, 85–90 (2019) doi:10.1038/s41586-019-1751-9