Synthesis and Radiation Damage of Vacancy-Ordered Double Perovskites, ((NH4)(1-x)FAx)2SnBr6

Degradation studies of the ASnX3 perovskites to the A2SnX6 vacancy-ordered double perovskite form have been well researched, but little is known about how A2SnX6 compounds degrade. In this work, a new double perovskite, FA2SnBr6 (FA = CH(NH2)2), was synthesised and characterised using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). FA2SnBr6 was found to crystallise in the P21/n monoclinic space group and showed the ability to form single-phase, solid solutions with another double perovskite (NH4)2SnBr6. Solid solutions of ((NH4)(1-x)FAx)2SnBr6, where x = 0.03, 0.04, 0.06, 0.09, were produced. X-ray radiation damage was investigated for ((NH4)(1-x)FAx)2SnBr6, where x = 0, 0.03, 0.09, 1, to qualitatively and quantitatively uncover degradation mechanisms. Correlation analysis, a new statistical analytical method for X-ray photoelectron spectra, was used to fortify peak fitting models. Comparing shifts in binding energies and relative atomic quantities between two elements constructs phase models from different spectral environments to understand the degradation of these compounds. In each radiation damage experiment, great consideration must be taken to combine the chemistry of the system and the physical process of photoelectron emission with the quantitative phase models formed. Overall, the presence of ammonium in the double perovskite enhances the stability of the compound to X-ray irradiation.