Spin State and Spin‐State Transition of Co3+ Ion in BiCoO3

Abstract

Confusion has arisen about the Co spin‐state transition under high pressure for multiferroic BiCoO3. The crystal structure analysis indicates a high‐spin (HS) to low‐spin (LS) state transition with increasing pressure, while Co Kβ X‐ray emission spectra present a high‐spin to intermediate‐spin (IS) state transition. Herein, the spin state of Co3+ in BiCoO3 is investigated utilizing soft X‐ray absorption spectroscopy (XAS) at the Co‐L2,3 and O‐K edges at room temperature under ambient pressure. Furthermore, the spin state transition of Co3+ under high pressure is investigated by Co Kβ X‐ray emission spectra. A pure HS‐Co3+ ground state is found in the BiCoO3 sample prepared from the precursor and oxidizer mixed method—and the existence of a small part of LS‐Co3+ in the BiCoO3 sample prepared from the precursor and oxidizer sandwiched method. A complete HS‐Co3+ to LS‐Co3+ transition is observed under high pressure up to 32.3 GPa. The results clarify the debate on the spin‐state transition of BiCoO3 under high pressure and will deepen our understanding of the intrinsic physical properties on it.