Mind the Mines: Lapieite Minerals with Ultralow Lattice Thermal Conductivity and High Power Factor for Thermoelectricity

To realize the widespread use of thermoelectric (TE) applications, developing low-cost, eco-friendly, and high-performance TE materials with an optimal band gap is essential. We find that the lapieite group─rock-forming minerals buried deep in the earth─with the general formula MCuPnQ3 (M = Ni, Pt, and Pd; Pn = Sb and Bi; and Q = S and Se) comprise the key metrics to become "Thermoelectric Rockstars". Our detailed chemical and phonon analyses show that the coexistence of weak covalent, partially ionic, and metavalent bonds and the stereoactive lone-pair electrons on Pn benefit the thermoelectric performance of the lapieite group. In PdCuBiSe3, for example, the elongated and soft Cu–Q and Pn–Q bonds along the c-axis synergistically suppress the lattice heat transport (κL) to 0.3 W m–1 K–1 and improve the power factor to 3 mW m–1 K–2 at 600 K, approaching the so-called "phonon-glass electron-crystal" paradigm. Likewise, the other members of the lapieite group achieve a high TE performance. The band structure and Fermi surface analyses indicate that the high band degeneracy (Nv = 11) contributes to their high TE performance. Thus, the minerals of the lapieite group, having nontoxic and earth-abundant elements, such as the Ni-based ones, open up a quick path for developing new practical TE materials, awaiting further experimental validations.