Electronic structure of ACu(3)Co(4)O(12) (A = Y, La, Bi): Synthesis, characterization, core-level spectroscopies, high-pressure application, and ab initio calculation

We present a comprehensive experimental and computational study on A-site ordered perovskite oxides YCu3Co4O12, LaCu3Co4O12, and BiCu3Co4O12 including synthesis, transport, and magnetic characterization, high-pressure application, K- and L-edge x-ray absorption spectroscopy (XAS), Co 2p core-level x-ray photoemission spectroscopy and density-functional theory (DFT) calculations combined with dynamical mean-field theory (DMFT) and +U scheme. An insulating behavior with a valence state of A(3+) Cu-3(similar to 3+) Co-4(similar to 3+) O-12(2-) is found for the three compounds at ambient and high-pressure conditions (up to similar to 55 GPa). A DFT calculation for YCu3Co4O12 uncovers the energetics of the Cu-O and Co-O bonding formation and crystal-field splitting, leading to a narrow-gap electronic structure with a hybrid orbital and element character near the Fermi energy. The stable low-spin configuration of the Co ion is studied in comparison to a canonical perovskite cobaltite LaCoO3. A DFT+ DMFT analysis of the Cu spin-correlation function indicates that the Zhang-Rice singlet description for the CuO4 plaquette is valid, while a hybridization with the Co 3d orbitals also contributes to the Cu spin screening. The presence of the hybridization between the Co and Cu orbitals is shown by the DFT + DMFT analysis for the Co L-2,L-3 XAS experimental spectra that exhibit unusual broad line shape. An increasing behavior of electrical resistance at elevated pressures is observed in all compounds and is interpreted based on a DFT + U simulation.

Automated summary

We conducted a comprehensive study on A-site ordered perovskite oxides YCu3Co4O12, LaCu3Co4O12, and BiCu3Co4O12, including synthesis, transport, and magnetic characterization, high-pressure application, x-ray absorption spectroscopy, x-ray photoemission spectroscopy, and density-functional theory (DFT) calculations. Our findings reveal insulating behavior and a valence state of A(3+) Cu-3(similar to 3+) Co-4(similar to 3+) O-12(2-) for all three compounds. DFT calculations uncover the energetics of bonding formation and crystal-field splitting, resulting in a narrow-gap electronic structure with hybrid orbitals near the Fermi energy. The presence of hybridization between Co and Cu orbitals is also shown through analysis of experimental spectra.