Frequency and temperature-dependent dielectric characteristics of lead- free Br doped perovskites (CH3NH3)3Bi2Cl9 and (CH3NH3)3Bi2BrxCl9-x

We report the synthesis and dielectric characteristics of lead-free methylammonium bismuth chloride (MABiCl) and Br doped methylammonium bismuth chloride (MABiBrCl) in powder form. The morphology of the samples showed growth of large flakes with large surface area. The band gaps of the perovskites are obtained from optical absorption data. The dielectric characteristics of the samples were measured in the frequency range 1 Hz to 1 MHz and temperature range 100-300 K. The data shows a complex electrical transport in these halide perovskite materials. The dielectric permittivity data shows the existence of a critical temperature at which the material undergoes a structural phase transition. The transition temper-ature is found to be 270 K and 266 K for MABiCl and MABiBrCl respectively. The results can be explained by certain change in orientation of methyl-ammonium (MA) ions as the temperature is increased.Copyright (c) 2022 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the Condensed Matter Phy-sics.