Transformation of Perovskite BaBiO3 into Layered BaBiO2.5 Crystals Featuring Unusual Chemical Bonding and Luminescence
Graphical Coordination environment engineering : Layered stoichiometric BaBiO 2.5 , synthesized by nontopotactic transformation of perovskite BaBiO 3 , features an unusual electron-density distribution and Bi−O bonding situation featuring one ionic and three covalent bonds, which give rise to peculiar near-infrared luminescence never seen before in any Bi-containing system (see figure). Engineering oxygen coordination environments of cations in oxides has received intense interest thanks to the opportunities for the discovery of novel oxides with unusual properties. Herein, the synthesis of stoichiometric layered BaBiO 2.5 by a nontopotactic phase transformation of perovskite BaBiO 3 is presented. By analyzing the synchrotron X-ray diffraction data by the maximum-entropy method/Rietveld technique, it was found that Bi is involved in an unusual chemical bonding situation with four oxygen atoms featuring one ionic bond and three covalent bonds, which results in an asymmetric coordination geometry. Photophysical characterization revealed that this peculiar structure shows near-infrared luminescence differing from that of conventional Bi-containing compounds. Experimental and theoretical results led to the proposal of an excitonic nature of the luminescence. This work highlights that synthesizing materials with uncommon Bi−O bonding and Bi coordination geometry provides a pathway to the discovery of systems with new functionalities. This could inspire interest in the exploration of a range of materials containing heavier p-block elements with prospects for finding systems with unusual properties.
危险品化学品经营许可证（带存储）