sp 2 to sp 3 Hybridization Transformation in Ionic Crystals under Unprecedentedly Low Pressure.

Under cold pressure sp 1 /sp 2 -to-sp 3 hybridization transformation has been exclusively observed in covalent or molecular crystals overwhelmingly above ≈10 GPa, and the approaches to lower the transition pressure are limited on external heat-treatment and/or catalyzers. Herein we demonstrate that, by internal-lattice stress-transfer from ionic to covalent groups, the transformation can be significantly prompted, as shown in a crystal of LiBO 2 under 2.85 GPa for the first case in ionic crystals. This unprecedentedly low transformation pressure is ascribed to the enhanced localized stress on covalent B-O frames transferred from ionic Li-O bonds in LiBO 2 , and accordingly the corresponding structural feature is summarized. This work provides an internal structural regulation strategy for pressure-reduction of the s-p orbital hybridization transformation and extends the sp 1 /sp 2 -to-sp 3 transformation landscape from molecular and covalent compounds to ionic systems.