The impact of the SnI2 purity on the formation of CsSnI3 perovskite modifications as monitored by 127I Nuclear Quadrupole Resonance

The relative content of the perovskite phase in two CsSnI₃ samples (of 99.900 and 99.999 wt% SnI₂ and 99.999 wt% CsI purity) was estimated using ¹²⁷I NQR. The results showed that both samples contained the non-perovskite orthorhombic phase as an admixture. In the sample of higher purity (99.999 wt%) its content was insignificant – only trace amounts could be observed at 77 K, whereas at room temperature the presence of the non-perovskite phase was not revealed. However, in the sample of 99.900 wt% purity the content of the non-perovskite phase has reached at least a third of the sample amount, which is due to the probable crystallization of the non-perovskite phase on impurities.