Comment on “Air-stable double halide perovskite Cs2CuBiBr6: synthesis and memristor application” by A. Betal, A. Chetia, D. Saikia, K. Karmakar, G. Bera, N. V. Dambhare, A. K. Rath and S. Sahu, Phys. Chem. Chem. Phys., 2025, 27, 3150
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Abstract
The recent claim by Betal et al. (Phys. Chem. Chem. Phys., 2025, 27, 3150) of synthesizing the air-stable Cs2CuBiBr6 double perovskite challenges the established thermodynamic instability of Cu(I)-based halide perovskites. Through rigorous reanalysis of their data, we demonstrate three critical inconsistencies: (1) X-ray diffraction patterns diverge markedly from simulated Cs2CuBiBr6 and Cs2AgBiBr6 patterns; (2) energy-dispersive X-ray spectroscopy reveals a Cu(I) : Bi(III) atomic ratio of ∼2 : 3, violating the 1 : 1 stoichiometry required for A2B(I)B(III)X6 perovskites; and (3) the reported bandgap (2.93 eV) exceeds that of Cs2AgBiBr6 (1.8–2.3 eV), contradicting the chemical trend predicted by density functional theory. Further, thermodynamic analysis confirms Cs2CuBiBr6's intrinsic instability (with a large negative decomposition energy of −35 meV per atom), disfavoring its synthesis. These findings bring into question Betal et al.'s claims and underscore the profound challenges in stabilizing Cu(I)-based double perovskites, urging stringent validation of structural, compositional, and thermodynamic data in perovskite research.
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