High potential thermoelectric figure of merit in ternary La(3)Cu(3)X(4) (X = P, As, Sb and Bi) compounds

We investigate the thermoelectric properties of the relatively unexplored rare-earth ternary compounds La(3)Cu(3)X(4) (X = Bi, Sb, As, and P) using first principles electronic structure and Boltzmann transport calculations. These compounds, of which the La(3)Cu(3)Sb(4) and La(3)Cu(3)Bi(4) 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 La(3)Cu(3)P(4) and La(3)Cu(3)As(4), 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.