Pressure‐Driven Two‐Step Second‐Harmonic‐Generation Switching in BiOIO3

Abstract Materials with multi‐stabilities controllable by external stimuli have potential for high‐capacity information storage and switch devices. Herein, we report the observation of pressure‐driven two‐step second‐harmonic‐generation (SHG) switching in polar BiOIO 3 for the first time. Structure analyses reveal two pressure‐induced phase transitions in BiOIO 3 from the ambient noncentrosymmetric phase (SHG‐high) to an intermediate noncentrosymmetric phase (SHG‐intermediate) and then to a centrosymmetric phase (SHG‐off). The three‐state SHG switching was inspected by in situ high‐pressure powder SHG and polarization‐dependent single‐crystal SHG measurements. Local structure analyses based on the in situ Raman spectra and X‐ray absorption spectra reveal that the SHG switching is caused by the step‐wise suppression of lone‐pair electrons on the [IO 3 ] − units. The dramatic evolution of the functional units under compression also leads to subtle changes of the optical absorption edge of BiOIO 3 . Materials with switchable multi‐stabilities provide a state‐of‐art platform for next‐generation switch and information storage devices.