On the Fate of Lithium Ions in Sol–Gel Derived Zinc Oxide Nanocrystals
Natalia Olejnik-Fehér, Maria Jędrzejewska, Małgorzata Wolska-Pietkiewicz, Daniel Lee, Gaël De Paëpe,* Janusz Lewiński*
Abstract: Among diverse chemical synthetic approaches to zinc oxide nanocrystals (ZnO NCs), ubiquitous inorganic sol–gel methodology proved crucial for advancements in ZnO-based nanoscience. Strikingly, unlike the exquisite level of control over morphology and size dispersity achieved in ZnO NC syntheses, the purity of the crystalline phase, as well as the understanding of the surface structure and the character of the inorganic–organic interface, have been limited to vague descriptors until very recently. Herein, ZnO NCs applying the standard sol–gel synthetic protocol are synthesized with zinc acetate and lithium hydroxide and tracked the integration of lithium (Li) cations into the interior and exterior of nanoparticles by combining various techniques, including advanced solid-state NMR methods. In contrast to common views, it is demonstrated that Li+ ions remain kinetically trapped in the inorganic core, enter into a shallow subsurface layer, and generate “swelling” of the surface and interface regions. Thus, this work enabled both the determination of the NCs’ structural imperfections and an in-depth understanding of the unappreciated role of the Li+ ions in impacting the doping and the passivation of sol–gel-derived ZnO nanomaterials.
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Unprecedented Richness of Temperature- and Pressure-Induced Polymorphism in 1D Lead Iodide Perovskite
Marcin Saski, Szymon Sobczak, Paulina Ratajczyk, Michał Terlecki, Wojciech Marynowski, Aleksandra Borkenhagen, Iwona Justyniak,* Andrzej Katrusiak,* Janusz Lewiński*
Abstract: Inherent features of metal halide perovskites are their softness, complex lattice dynamics, and phase transitions spectacularly tuning their structures and properties. While the structural transformations are well described and classified in 3D perovskites, their 1D analogs are much less understood. Herein, both temperature- and pressure-dependent structural evolutions of a 1D AcaPbI3 perovskitoid incorporating acetamidinium (Aca) cation are examined. The study reveals the existence of nine phases of δ-AcaPbI3, which present the most diverse polymorphic collection among known perovskite materials. Interestingly, temperature- and pressure-triggered phase transitions in the 1D perovskotoid exhibit fundamentally different natures: the thermal transformations are mainly associated with the collective translations of rigid polyanionic units and ordering/disordering dynamics of Aca cations, while the compression primarily affects inorganic polymer chains. Moreover, in the 1-D chains featuring the face-sharing connection mode of the PbI6 octahedra the Pb···Pb distances are significantly shortened compared to the corner-sharing 3D perovskite frameworks, hence operating in the van der Waals territory. Strikingly, a good correlation is found between the Pb···Pb distances and the pressure evolution of the bandgap values in the δ-AcaPbI3, indicating that in 1D perovskitoid structures, the contacts between Pb2+ ions are one of the critical parameters determining their properties.