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.