Phonon-drag effect inFeGa3

Abstract

The thermoelectric properties of single-and polycrystalline FeGa3 are systematically investigated over a wide temperature range. At low temperatures, below 20 K, previously not known pronounced peaks in the thermal conductivity (400-800 W K −1 m −1 ) with corresponding maxima in the thermopower (in the order of -16000 µV K −1 ) were found in single crystalline samples. Measurements in single crystals along [100] and [001] directions indicate only a slight anisotropy in both the electrical and thermal transport. From susceptibility and heat capacity measurements, a magnetic or structural phase transition was excluded. Using density functional theory-based calculations, we have revisited the electronic structure of FeGa3 and compared the magnetic (including correlations) and non-magnetic electronic densities of states. Thermopower at fixed carrier concentrations are calculated using semi-classical Boltzmann transport theory, and the calculated results match fairly with our experimental data. The inclusion of strong electron correlations treated in a mean-field manner (by LSDA+U ) does not improve this comparison, rendering strong correlations as the sole explanation for the low temperature enhancement unlikely. Eventually, after a careful review, we assign the peaks in the thermopower as a manifestation of the phonon-drag effect, which is supported by thermopower measurements in a magnetic field.

Arsenene and Antimonene: Two-Dimensional Materials with High Thermoelectric Figures of Merit

“…With the second-and third-order force constants as input, κ l can be calculated using the SHENGBTE code [51,52]. No drawbacks are expected from the fact that phonon drag is not considered in this approach, because, at the elevated temperatures relevant for most thermoelectric applications, the contributions to S are negligible [53]. The second-order force constants are determined by PHONOPY [54] with a 5 × 5 × 1 supercell and a 4 × 4 × 1 k mesh.…”

Unprecedented Integral-Free Debye Temperature Formulas: Sample Applications to Heat Capacities of ZnSe and ZnTe

“…), are quantifying the material-specific weights of contributions of the individual, anharmonicityrelated power terms [15,21,54,57]. Furthermore we have still included into (5) an additional linear term, ( ) ( ) = 1 , which has to represent possible contributions of a degenerate electronic system [4,6,13,23,[60][61][62][63] to the measured heat capacities. Such electronic contributions ("Sommerfeld terms" [4,6,60]) are known to be rather strong (tending to become even the dominant ones, at sufficiently low temperatures) in metals, due to large concentrations of conduction electrons.…”

“…Figure 2) and for ZnTe (Figure 3), using (5) in combination with (9) and (14) to (17). In the lower part of Table 1 [63]). Such electronic contributions are analytically represented within the present context by the respective linear (electronic) term, ( ) ( ) = 1 , in (5).…”

“…where the 1 term [4,6,13,23,[60][61][62][63] represents a possible electronic contribution and the subsequent three oddorder terms are due to harmonic lattice contributions. Of special interest in this connection is the lowest-order lattice contribution, 3 3 , which corresponds to Debye's classical ( → 0 limiting) cubic law [1,3,6,8,21], ℎ ( → 0) ∝ 3 .…”

“…Consequently, within the frame of the frequently adopted ( )/ versus 2 representation [4,6,13,15,46,62,63,83] ( )…”