J.S. acknowledges support from the MRSEC program (DMR-1720319) at the Materials Research Center of Northwestern University (overall leadership of the project, DFT convex hull calculations). D.G., T.L., and C.W. acknowledge financial support received from Toyota Research Institute (TRI) through the Accelerated Materials Design and Discovery program (phonon calculations), S.S. and Z.L. acknowledge the Department of Energy, Office of Science, Basic Energy Sciences under grant DE-SC0014520 (band structure calculations). S.G. acknowledges the U.S. Department of Commerce and National Institute of Standards and Technology as part of the Center for Hierarchical Materials Design (CHiMaD) under award no. 70NANB14H012 (DFT calculations). A.S.C. acknowledges the financial support to National Agency for Research and Development (ANID)/DOCTORADO BECAS CHILE/2018-56180024. T.L. also acknowledges the financial support received from Taiwanese Government Fellowship (Cu-substitution discussion). D.K. acknowledges funding from the International Institute for Nanotechnology (IIN) and the Predictive Science and Engineering Design (PSED) Program at Northwestern University (DFT calculations). Y.X. acknowledges partial support from the US National Science Foundation through Award No. 2317008. All authors acknowledge the computational resources of the Bridges-2 supercomputer at Pittsburgh Supercomputer Center (PSC) under grant no. DMR160112 (DFT calculations for band and DOS) and the Quest high-performance computing facility at Northwestern University. This research used the computational resources of the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility located at Lawrence Berkeley National Laboratory, operated under Contract no. DE-AC02-05CH11231 using NERSC award BES-ERCAP23792.
American Chemical Society
Chemical structures -- Phonons, Phonons -- Optical properties
Recently, Cu-substituted lead apatite LK-99 was reported to have room-temperature ambientpressure superconductivity. Here we utilize density functional theory (DFT) total energy and harmonic phonon calculations to investigate the thermodynamic and dynamic stability of two lead phosphate apatites in their pure and Cu-substituted structures. Though Pb10(PO4)6O and Pb10(PO4)6(OH)2 are found to be thermodynamically stable (i.e., on the T=0K ground state convex hull), their Cu-substituted counterparts are above the convex hull. Harmonic phonon calculations reveal dynamic instabilities in all four of these structures. Oxygen vacancy formation energies demonstrate that the addition of Cu dopant substituting for Pb increases the likelihood of the formation of oxygen vacancies on the anion site. We propose a new possible phase in this system, Pb8Cu2(PO4)6, where two monovalent Cu atoms are substituted for two Pb(1) atoms and the anion oxygen is removed. We also propose several reaction pathways for Pb9Cu(PO4)6O and Pb8Cu2(PO4)6, and found that both of these two structures are likely to be synthesized under a 1:1 ratio of reactants Pb2SO5 and Cu3P. Our work provides a thorough foundation for the thermodynamic and dynamic stabilities of LK-99 related compounds and we propose several possible novel synthesis reaction pathways and a new predicted structure for future studies.
© Copyright the author(s) 2023
Locate the Document
Published as: Chem. Mater. 2024, 36, 1, 275–285 Publication Date:December 18, 2023 https://doi.org/10.1021/acs.chemmater.3c02054 Copyright © 2023 American Chemical Society