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

Under cold pressure sp1 /sp2 -to-sp3 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 LiBO2 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 LiBO2 , 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 sp1 /sp2 -to-sp3 transformation landscape from molecular and covalent compounds to ionic systems.