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Updated: Jan 19, 2026
Melting and Freezing; Energetics of Melting and Fusion
Methylammonium Polyiodides: Remarkable Phase Diversity of the Simplest and Low-Melting Alkylammonium Polyiodide
Andrey A Petrov1, Sergey A Fateev1, Yan V Zubavichus2
1Laboratory of New Materials for Solar Energetics, Department of Materials Science , Lomonosov Moscow State University , 1 Lenin Hills, 119991 Moscow , Russia.
Abstract:
Newly discovered methylammonium polyiodides (MAI) are unique precursors for innovative solvent-free technologies in perovskite photovoltaics because MAI are liquids at room temperature and demonstrate high chemical reactivity. We investigated the features of an MAI-I2 system and built up a first phase diagram in wide temperature and composition ranges using data from differential scanning calorimetry, single-crystal X-ray diffraction, and visual thermal analysis. The phase diagram has been found to differ drastically from that of any related systems owing to the unique propensity of methylammonium toward forming a diversity of polyiodides with complicated crystal structures, namely, MAI2, MAI2.67, MAI4, and MAI5.5, found in this system for the first time. The performed density functional theory calculations revealed the crucial role of entropy contributing to the formation of higher methylammonium polyiodides, in good agreement with experimental data.
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