Roterbärite, PdCuBiSe3, a new mineral species from the Roter Bär mine, Harz Mountains, Germany

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

“…Minerals of the lapieite grouplapieite (NiCuSbS 3 ), mückeite (NiCuBiS 3 ), malyshevite (PdCuBiS 3 ), lisiguangite (PtCuBiS 3 ), and roterbärite (PdCuBiSe 3 )belong to a vast group of sulfosalts. ,,, The only seleniosalt of this family is roterbärite, recently collected from the Roterbär mine, Germany . All these isostructural minerals with the general formula MCuPnQ 3 (M = Ni, Pt, and Pd; Pn = Sb and Bi; and Q = S and Se) crystallize in an orthorhombic P 2 1 2 1 2 1 space group, as shown in Figure .…”

“…27,30,44,45 The only seleniosalt of this family is roterbarite, recently collected from the Roterbar mine, Germany. 30 All these isostructural minerals with the general formula MCuPnQ 3 (M = Ni, Pt, and Pd; Pn = Sb and Bi; and Q = S and Se) crystallize in an orthorhombic P2 1 2 1 2 1 space group, as shown in Figure 1. The 24-atom unit cell of the lapieite structure type contains three independent cations (M, Cu, and Pn) and three independent chalcogen atoms.…”

“…The Pn−Q bond along the c-axis is 30% longer (i.e., weaker) than the other three bonds, consistent with the 3 + 1 scheme found in the experiment. 30 Pd and Cu also form weak bonds with neighboring chalcogens, evident from their small ICOHP.…”

“…As listed in Table S3 (Supporting Information), Z xx * values of Bi and Sb along the a-axis (i.e., LEP direction) are, respectively, 4.8 and 4.7, exceeding their conventional nominal charge in lapieites. 30 A sterically active LEP distorts the BiQ 4 units, repels negatively charged anions, and finally results in bond heterogeneity 60,65 and lattice anharmonicity. 65 The LEP-induced anharmonicity is confirmed via the displacement of a Bi atom in PdCuBiSe 3 along the LEP direction (i.e., the a-axis).…”

“…The diverse bondings together with the anharmonic vibrations of Pn atoms, owing to their s 2 stereoactive lone electron pair (LEP), boost phonon–phonon scattering rates and further suppress lattice heat transport in lapieites. Among them, PdCuBiSe 3 dubbed roterbärite, mined in 2020 from Harz Mountain, Germanystands out with κ L zz ≈ 0.3 W m –1 K –1 and a hole-doped PF ≈ 3 mW m –1 K –2 at 600 K. Not only roterbärite but also other lapieites are promising rock-forming minerals for thermoelectricity, called here “TE Rockstars”, whose TE performance could, of course, be further improved by entropy, band, and phonon engineering methods, ,, as recently realized in lillianite minerals …”