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Compositional Variation in Hybrid Organic–Inorganic Lead Halide Perovskites: Kinetically versus Thermodynamically Controlled Synthesis

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journal contribution
posted on 13.05.2021, 18:36 by Jiyu Tian, Eli Zysman-Colman, Finlay D. Morrison
The formation and study of partial solid solutions in Az1–xFAxPbBr3, using reportedly similar-sized cations azetidinium (Az+) and formamidinium (FA+), were explored via mechanosynthesis and precipitation synthesis. The compositions and lattice parameters of samples from both syntheses were analyzed by 1H NMR and Rietveld refinement of powder X-ray diffraction. A clear mismatch in the composition of the perovskite was found between the precipitated samples and the corresponding solutions. Such a mismatch was not observed for samples obtained via mechanosynthesis. The discrepancy suggests that products are kinetically controlled during precipitation compared to thermodynamically controlled mechanosynthesis. Furthermore, the cell volume as a function of composition in both hexagonal, 6H (Az-rich), and cubic, 3C (FA-rich), perovskite solid solutions suggests that FA+ is actually smaller than Az+, contradicting the literature. In the 3C (Az-poor) solid solutions, the extent of Az1–xFAxPbBr3 is unexpectedly smaller than that in the corresponding methylammonium (MA+) system, Az1–xMAxPbBr3, which suggests that the extent of solid-solution formation in these halide perovskites is predominantly dependent on the average A-cation size while the size mismatch plays a lesser role in comparison to oxides.