Abstract:We report an investigation of the thermoelectric properties of Mg2Ge1−xSnx solid solution with x = 0.5 using models based on first-principles calculations and experimental data. The model gives transport properties including the figure of merit ZT as functions of carrier concentration and temperature. The model for n-type predicts high ZT at optimized doping, and suggests that the ZT value can exceed 2 at T = 1000 K.
“…That result confirms earlier predictions [6][7][8][9][10] that the phonons are the main mechanism for thermal conductivity and thus lattice modification through reducing of material dimensionality is reasonable [7]. Moreover calculations show presence of soft phonons mods suppressing thermal energy in material [5,6,9]. The value of thermal conductivity is also low because of multiphase structure of the sample [11].…”
Section: Resultssupporting
confidence: 76%
“…That powder contains mainly oxidation products. Recently, these materials were studied using ab-initio calculations and they were predicted to possess very promising thermopower [5][6][7][8][9][10]. Its real crystal structure is also a matter of debate [3,8,9].…”
We measured thermopower, thermal conductivity and electrical resitivity for Ca2Sn sample across 4-350 K temperature range. Contrary to expectations from recent DFT based calculations the thermopower is not particularly large, reaching 7 µV at 350 K. The thermoelectric figure of merit renders this material in unmodified form practically unusable for thermoelectric aplications.
“…That result confirms earlier predictions [6][7][8][9][10] that the phonons are the main mechanism for thermal conductivity and thus lattice modification through reducing of material dimensionality is reasonable [7]. Moreover calculations show presence of soft phonons mods suppressing thermal energy in material [5,6,9]. The value of thermal conductivity is also low because of multiphase structure of the sample [11].…”
Section: Resultssupporting
confidence: 76%
“…That powder contains mainly oxidation products. Recently, these materials were studied using ab-initio calculations and they were predicted to possess very promising thermopower [5][6][7][8][9][10]. Its real crystal structure is also a matter of debate [3,8,9].…”
We measured thermopower, thermal conductivity and electrical resitivity for Ca2Sn sample across 4-350 K temperature range. Contrary to expectations from recent DFT based calculations the thermopower is not particularly large, reaching 7 µV at 350 K. The thermoelectric figure of merit renders this material in unmodified form practically unusable for thermoelectric aplications.
“…To put our calculated ZT values in real perspective we compare these with recent theoretical studies, where similar methodologies were employed. For instance a ZT of 1.75, 0.8, 1.75, 0.9, and 1.9 has been reported for Mg 2 Ge 0.5 Sn 0.5 (1000 K) 7 , Bi 2 S 3 (750 K) 66 , BaCd 2 Sb 2 (950 K) 67 , WS 2 (1500 K) 68 and Si 2 Te 3 (1000 K) 69 , respectively. Thus, the calculated ZT values of La based compounds are comparable with the other theoretically reported values for a variety of materials.Figure 6Calculated figure of merit as function of temperature for La 3 Cu 3 P 4 , La 3 Cu 3 As 4 , La 3 Cu 3 Sb 4 , and La 3 Cu 3 Bi 4 under p -type doping.…”
We investigate the thermoelectric properties of the relatively unexplored rare-earth ternary compounds La3Cu3X4 (X = Bi, Sb, As, and P) using first principles electronic structure and Boltzmann transport calculations. These compounds, of which the La3Cu3Sb4 and La3Cu3Bi4 have previously been synthesized, are all predicted to be semiconductors and present a wide range of bandgaps varying from 0.24 eV (for the Bi compound) to 0.87 eV (for the P compound). We further find a mixture of light and heavy bands, which results in a high thermoelectric power factor. In addition, as discussed in our previous study (Phys. Rev. B 95 (22), 224306, 2017) at high temperatures of 1000 K these compounds exhibit lattice thermal conductivity less than 1 W/mK. The combination of low thermal conductivity and good transport properties results in a predicted ZT as high as ~1.5 for both La3Cu3P4 and La3Cu3As4, under high p-type doping. This predicted high performance makes these compounds promising candidates for high temperature thermoelectric applications and thus merits further experimental investigation.
“…Nevertheless, this does not mean we can limitlessly increase the power factor and reduce the thermal conductivity, because these parameters are always coupled with each other. Therefore, different strategies have been taken to improve the ZT value, including doping [4,5], band engineering [6,7] and low dimensional structure [8,9], etc.…”
Recent experiments indicated that both layered Bi 2 O 2 Se and Bi 2 O 2 Te are promising thermoelectric materials with low thermal conductivities. However, theoretical study on the thermoelectric properties, especially the phonon transport properties, is rare. In order to understand the thermoelectric transport mechanism, we here investigate the electron and phonon transport properties by using the first-principles calculations combined with the Boltzmann transport theory.Our results indicate that both Bi 2 O 2 Se and Bi 2 O 2 Te are semiconductors with indirect energy gaps of 0.87 eV and 0.21 eV within spin-orbit coupling, respectively. Large Seebeck coefficient and power factor are found in the p-type than the n-type for both compounds. Low lattice thermal conductivities at room temperature are obtained, 1.14 W m −1 K −1 for Bi 2 O 2 Se and 0.58 W m −1 K −1 for Bi 2 O 2 Te, which are close to the experimental values. It is found that the low-frequency optical phonon branches with higher group velocity and longer lifetime also make a main contribution to the lattice thermal conductivity. Interestingly, the lattice thermal conductivity exhibits obvious anisotropy especially for Bi 2 O 2 Te. These results are helpful for the understanding and optimization of thermoelectric performance of layered Bi 2 O 2 Se and Bi 2 O 2 Te.
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