The work performed at the FZU represents a significant contribution to the field of sustainable energy and materials science, addressing the crucial global need for efficient heat-to-electricity conversion. Thermoelectric devices, which enable this conversion by utilizing a temperature difference to circulate charge carriers in semiconductors, are gaining renewed interest for their potential in waste-heat recovery and overall energy efficiency improvement. Scandium Nitride (ScN) has emerged as a particularly promising material in this domain due to its high-symmetry rocksalt crystal structure, which offers opportunities for band structure engineering to achieve low electrical resistivity and low thermal conductivity. While ScN has a high power factor, its main limitation has historically been its relatively high thermal conductivity (∼10 to 12 Wm−1K−1 to room temperature in thick films), which limits its practical thermoelectric figure of merit (ZT) to low values (0.05–0.15). The research detailed below successfully addresses this challenge through advanced materials engineering.
This groundbreaking research on ScN-based materials was conducted by Joris More-Chevalier, along with collaborators, as part of the Laser Technologies group within the Department of Analysis of Functional Materials (28) at FZU, focusing on new thermoelectric systems for heat conversion. This research is connected to the Czech Science Foundation (GAČR) project No. 23-07228S, supervised by Ing. Michal Novotný, Ph.D. from FZU and Dominik Legut, Ph.D. from IT4Innovations, VSB - Technical University of Ostrava.
Enhancing Thermoelectric Properties of ScN
The primary goal of this research was to significantly improve the thermoelectric efficiency, which is quantified by the dimensionless figure of merit (ZT). Two distinct strategies were explored to manipulate the ScN film microstructure: incorporating twin domains and forming ScN/Sc1−xNbxNmultilayer structures.
Engineering with Twin Domains
In one approach, ScN layers deposited on MgO (001) substrates were intentionally engineered to contain a twin-domain structure (denoted as ScN-T) by periodically interrupting the operation of one magnetron cathode during the DC reactive magnetron sputtering process (Figure 1). This structural modification proved to be a simple and stable solution for improving thermoelectric properties at elevated temperatures. Compared to the almost defect- and domain-free ScN layers, the ScN-T layers showed a marked enhancement in performance at 800 K. Specifically, the Seebeck coefficient (S) was enlarged by about 30% (from −64 μVK−1 to −82 μVK−1 at 800 K), and the resulting experimental lower limit of the figure of merit was increased over two and a half times (reaching ∼0.2 at 800 K). A major factor in this improvement was the drastic reduction in thermal conductivity (κ): 10.06 Wm −1K −1 for ScN was reduced to 2.85 Wm −1K −1 for ScN-T at 300 K. This improvement arose predominantly from the presence of the twin domains, which suppressed acoustic phonon propagation, thereby lowering thermal conductivity, while simultaneously lowering electronic conductivity and enhancing the Seebeck coefficient due to twin domain boundaries. The surface morphology observed using Atomic Force Microscopy (AFM) in ScN-T confirmed this, revealing pyramidal-shaped grains characteristic of twinning in the {111} planes, mixed with the square-shaped grains of the 001 orientation.
Figure 1: Enhancing thermoelectric properties of ScN films through twin domains [1].
Multilayer Engineering with Niobium Doping
The second strategy involved depositing multilayers to utilize diffusion-driven doping and boundary scattering. Four multilayers were created with overall Niobium (Nb) atomic percentages ranging from 0.4% to 4.8% (Figure 2). Transmission Electron Microscopy (TEM) confirmed the epitaxial growth and layered structure, with Nb preferentially incorporated into distinct, thin sublayers. These multilayers showed improved thermoelectric properties as the Nb multilayer doping increased the Seebeck coefficient and reduced the thermal conductivity. For instance, the samples with 1.2% and 1.8% Nb achieved Seebeck coefficients of −110 μV/K and −116 μV/K at 800 K, respectively, compared to −64 μV/K for the undoped ScN. Additionally, the thermal conductivity decreased considerably from 10.06 Wm−1K−1 to 4 Wm−1K−1 at room temperature for these doped samples. This dual enhancement led to a notable potential increase in the ZT to over 0.3 at 800 K for the 1.2% and 1.8% Nb samples, demonstrating the promise of this multilayer approach.
Analytical Support and Validation
Throughout the research, sophisticated analytical techniques and theoretical modeling were integral to both understanding and validating the experimental results. Raman spectroscopy was used to explore the temperature effect on the phonon dynamics, confirming a concentration-dependent redshift of the optical phonon modes due to the substitution of the lighter Sc atoms by the heavier Nb atoms. First-principles studies using Density Functional Theory (DFT) and ab initio molecular dynamics (AIMD) simulations supported the experimental findings, providing detailed insights into the electronic and lattice contributions to thermal conductivity. The calculated thermoelectric transport coefficients (Seebeck coefficient and electrical resistivity) closely matched the measured data for both the pure and Nb-doped ScN. The consistency between theory and experiment, particularly the successful prediction of reduced thermal conductivity and enhanced Seebeck coefficient, provided a strong foundation for the conclusions on material design.
Figure 2: Thermoelectric efficiency enhancement in ScN-based multilayers by Nb diffusion-driven doping [2].
References:
[1] J. More-Chevalier, et al, Enhancing thermoelectric properties of ScN films through twin domains, Applied Surface Science Advances 25 (2025) 100674. doi.org/10.1016/j.apsadv.2024.100674.
[2] J. More-Chevalier, et al, Thermoelectric efficiency enhancement in ScN-based multilayers by Nb diffusion-driven doping, Applied Surface Science Advances 29 (2025) 100821. doi.org/10.1016/j.apsadv.2025.100821
