Fig. 5

High-pressure structure modes of Fe2+ honeycomb lattice and comparison with FeSe-type tetragonal Fe2+ lattice. a The proposed HP-mode-1 for FePSe3 with slightly distorted Fe2+ honeycomb lattice. b The proposed HP-mode-2 for FePSe3 with seriously distorted Fe2+ honeycomb lattice. The shortest or the near-shortest Fe–Fe bond lengths are highlighted by black and gray lines in the HP-mode-1 and black and yellow lines in the HP-mode-2, respectively. c Tetragonal Fe2+ lattice in most Fe-based high-Tc superconductors with FeSe-type layered structures