Progressive polytypism and bandgap tuning in azetidinium lead halide perovskites

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Mixed halide azetidinium lead perovskites AzPbBr3xXx (X = Cl or I) were obtained by mechanosynthesis. With varying halide composition from Cl to Br to I, the chloride and bromide analogues both form in the hexagonal 6H polytype while the iodide adopts the 9R polytype. An intermediate 4H polytype is observed for mixed Br/I compositions. Overall, the structure progresses from 6H to 4H to 9R perovskite polytype with varying halide composition. Rietveld refinement of the powder X-ray diffraction patterns revealed a linear variation in unit cell volume as a function of the average radius of the anion, which not only is observed within the solid solution of each polytype (according to Vegard’s law) but also extends uniformly across all three polytypes. This is correlated to a progressive (linear) tuning of the bandgap from 3.43 to 2.00 eV. Regardless of halide, the family of azetidinium halide perovskite polytypes are highly stable, with no discernible change in properties over more than 6 months under ambient conditions.
Original languageEnglish
Pages (from-to)12247–12254
Number of pages8
JournalInorganic Chemistry
Issue number16
Early online date28 Jul 2021
Publication statusPublished - 16 Aug 2021


  • Anions
  • Diffraction
  • Inorganic compounds
  • Perovskites
  • Halogens


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