Inorganic metal halides offer unprecedented tunability through elemental variation of simple three-element compositions, but can exhibit complicated phase behaviour, degradation, and microscopic phenomena (disorder/dynamics) that play an integral role for the bulk-level chemical and physical properties of these materials. Understanding the halogen chemical environment in such materials is crucial to addressing many of the concerns regarding implementing these materials in commercial applications. In this study, a combined solid-state nuclear magnetic resonance, nuclear quadrupole resonance and quantum chemical computation approach is used to interrogate the Br chemical environment in a series of related inorganic lead bromide materials: CsPbBr3, CsPb2Br5, and Cs4PbBr6. The quadrupole coupling constants (CQ) were determined to range from 61 to 114 MHz for 81Br, with CsPbBr3 exhibiting the largest measured CQ and Cs4PbBr6 the smallest. GIPAW DFT was shown to be an excellent pre-screening tool for estimating the EFG of Br materials and can increase experimental efficiency by providing good starting estimates for acquisition. Finally, the combination of theory and experiment to inform the best methods for expanding further to the other quadrupolar halogens is discussed.
Keywords: Bromine; Chlorine; Electric field gradient; GIPAW DFT; Halogen; High fields; Iodine; Metal halides; NQR; Perovskites; Quadrupolar nuclei; SSNMR; Semiconductors.
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