Revealing the Electronic Origin of Pressure-Induced Isostructural Transformations in Ca3Co2O6

Structural peculiarities of Ca₃Co₂O₆, including its low dimensionality and inherent geometric frustration, are the main sources of the exotic physical properties observed for this material. Exploring the interplay between the lattice and other electronic degrees of freedom is crucial for understanding the mechanism governing its physical behavior. In this study, we present a comprehensive analysis of the structural features of Ca₃Co₂O₆ in a large pressure range of 0–30 GPa, utilizing a combination of x-ray diffraction and Raman spectroscopy, complemented by density functional theory calculations. Notably, we observe several isostructural modifications at 3 GPa, 10 GPa, and 22 GPa, which have not been detected elsewhere. These phase transitions are accompanied by anomalies in the pressure-dependent variation in Ca and O atomic positions and Co–O interatomic bonds. Bader charge analysis also reveals changes in charge redistribution trends among Co, Ca, and O across the phase transitions, suggesting an electronic origin for the pressure-induced isostructural transitions in Ca₃Co₂O₆.