Methylammonium Lead Iodide across Physical Space: Phase Boundaries and Structural Collapse.

Hybrid perovskites exhibit complex structures and phase behavior under different thermodynamic conditions and chemical environments, the understanding of which continues to be pivotally important for tailoring their properties toward improved operational stability. To this end, we present for the first time a comprehensive neutron and synchrotron diffraction investigation over the pressure-temperature phase diagram of the paradigmatic hybrid organic-inorganic perovskite methylammonium lead iodide (MAPbI). This ambitious experimental campaign down to cryogenic temperatures and tens of kilobars was supported by extensive molecular dynamics simulations validated by the experimental data, to track the structural evolution of MAPbI under external physical stimuli at the atomic and molecular levels.

Cation Dynamics as Structure Explorer in Hybrid Perovskites-The Case of MAPbI.

Hybrid organic-inorganic perovskites exhibit remarkable potential as cost-effective and high-efficiency materials for photovoltaic applications. Their exceptional chemical tunability opens further routes for optimizing their optical and electronic properties through structural engineering. Nevertheless, the extraordinary softness of the lattice, stemming from its interconnected organic-inorganic composition, unveils formidable challenges in structural characterization.

Unraveling the Ordered Phase of the Quintessential Hybrid Perovskite MAPbI─Thermophysics to the Rescue.

Hybrid perovskites continue to attract an enormous amount of attention, yet a robust microscopic picture of their different phases as well as the extent and nature of the disorder present remains elusive. Using specific-heat data along with high-resolution inelastic neutron scattering and ab initio modeling, we address this ongoing challenge for the case of the ordered phase of the quintessential hybrid-perovskite MAPbI. At low temperatures, the specific heat of MAPbI reveals strong deviations from the Debye limit, a common feature of pure hybrid perovskites and their mixtures.

Spectroscopic Signatures of Hydrogen-Bonding Motifs in Protonic Ionic Liquid Systems: Insights from Diethylammonium Nitrate in the Solid State.

Diethylammonium nitrate, [N][NO], and its perdeuterated analogue, [N ] [NO], were structurally characterized and studied by infrared, Raman, and inelastic neutron scattering (INS) spectroscopy. Using these experimental data along with state-of-the-art computational materials modeling, we report unambiguous spectroscopic signatures of hydrogen-bonding interactions between the two counterions. An exhaustive assignment of the spectral features observed with each technique has been provided, and a number of distinct modes related to NH···O dynamics have been identified.