Lattice thermal transport in La3Cu3X4 compounds (

Abstract

Thermal conductivity of La 3 Cu 3 X 4 (X=P, As, Sb, Bi) compounds are examined using firstprinciples density functional theory and Boltzmann transport methods. We observe a trend of increasing lattice thermal conductivity ( ) with increasing atomic mass, challenging our expectations as lighter mass systems typically have larger sound speeds and weaker intrinsic scattering. In particular, we find that La 3 Cu 3 P 4 has the lowest despite having larger sound speed and the most restricted available phase space for phonon-phonon scattering, an important criterion for estimating and comparing among like systems. The origin of this unusual behavior lies in the strength of the individual anharmonic phonon scattering matrix elements, which are much larger in La 3 Cu 3 P 4 than in the heavier La 3 Cu 3 Bi 4 system. Our finding provides insights into the interplay of harmonic and anharmonic properties of complex, low thermal conductivity compounds, of potential use for thermoelectric and thermal barrier coating applications.

High potential thermoelectric figure of merit in ternary La3Cu3X4 (X = P, As, Sb and Bi) compounds

“…As discussed in ref. 32 , the κ latt for P and As compounds is comparable with the state of the art thermoelectric materials such as PbTe 59 and Bi 2 Te 3 60,61 , indicating their potential for a good thermoelectric performance. This is counter-intuitive that despite of their lower atomic masses P and As exhibit lower κ latt ; as in general compounds with heavier atoms results in low value of κ latt .…”

“…In addition, these compounds exhibit structural and electronic features such as high band degeneracy, and combination of both heavy and light bands near the band edges, which yield high power factor. Furthermore as discussed in our recent study 32 , these compounds exhibit low lattice thermal conductivity (<1 W/mK) at high temperatures. By optimizing the ZT with respect to the doping concentrations at different temperatures, we find a peak ZT value of ~1.5 for p -type La 3 Cu 3 P 4 and La 3 Cu 3 As 4 at 1000 K at doping concentration of 7 × 10 20  cm −3 .…”

“…An enlarged version of Fig. 1(c,d) and its effect of lattice thermal conductivity is already published and discussed at length in our recent study 32 . Here phonon dispersions are presented to address the dynamical stability of these compounds.…”

“…Additionally, the room temperature lattice thermal conductivity ( κ latt ) as calculated in ref. 32 is also shown for comparison. Dagger( † ), represents structures generated by particle swarm optimization (PSO) algorithm using the Calypso code.…”

“…The lattice thermal conductivity ( κ latt ) of these compounds was calculated in our recent work 32 , where a low κ latt of 1W/mK was found at high temperatures (>900 K) for all four compounds. The 300 K κ latt for all four compounds are reproduced in Table 1 for comparison.…”