Electronic structure of ACu3Co4O12 ( A = Y, La, Bi): Synthesis, characterization, core-level spectroscopies, high-pressure…

We present a comprehensive experimental and computational study on $A$-site ordered perovskite oxides ${\mathrm{YCu}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{12}, {\mathrm{LaCu}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{12}$, and ${\mathrm{BiCu}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{12}$ 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 ${A}^{3+}{\mathrm{Cu}}_{3}^{\ensuremath{\sim}3+}{\mathrm{Co}}_{4}^{\ensuremath{\sim}3+}{\mathrm{O}}_{12}^{2\ensuremath{-}}$ is found for the three compounds at ambient and high-pressure conditions (up to $\ensuremath{\sim}55$ GPa). A DFT calculation for ${\mathrm{YCu}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{12}$ 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 ${\mathrm{LaCoO}}_{3}$. A $\mathrm{DFT}+\mathrm{DMFT}$ analysis of the Cu spin-correlation function indicates that the Zhang-Rice singlet description for the ${\mathrm{CuO}}_{4}$ 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 $\mathrm{DFT}+\mathrm{DMFT}$ analysis for the Co ${L}_{2,3}$ 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 $\mathrm{DFT}+U$ simulation.