Crystal and electronic structures of CaAl2Si2-type rare-earth copper zinc phosphides RECuZnP2 (RE=Pr, Nd, Gd–Tm, Lu)

Experimental validation of high thermoelectric performance in RECuZnP2 predicted by high-throughput DFT calculations

Accurate density functional theory calculations of the interrelated properties of thermoelectric materials entail high computational cost, especially as crystal structures increase in complexity and size. New methods involving ab initio scattering and transport (AMSET) and compressive sensing lattice dynamics are used to compute the transport properties of quaternary CaAl₂Si₂-type rare-earth phosphides RECuZnP₂ (RE = Pr, Nd, Er), which were identified to be promising thermoelectrics from high-throughput screening of 20 000 disordered compounds. Experimental measurements of the transport properties agree well with the computed values. Compounds with stiff bulk moduli (>80 GPa) and high speeds of sound (>3500 m s^-1) such as RECuZnP₂ are typically dismissed as thermoelectric materials because they are expected to exhibit high lattice thermal conductivity. However, RECuZnP₂ exhibits not only low electrical resistivity, but also low lattice thermal conductivity (∼1 W m^-1 K^-1). Contrary to prior assumptions, polar-optical phonon scattering was revealed by AMSET to be the primary mechanism limiting the electronic mobility of these compounds, raising questions about existing assumptions of scattering mechanisms in this class of thermoelectric materials. The resulting thermoelectric performance (zT of 0.5 for ErCuZnP₂ at 800 K) is among the best observed in phosphides and can likely be improved with further optimization.