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Ice, one of the most enigmatic materials on Earth, exhibits diverse polymorphism, with research mainly focusing on the most commonly observed phases: hexagonal ice (I h ), cubic ice (I c ), and stacking-disordered ice (I sd ). While their formation or structural changes are crucial for advancements in cloud science, climate modeling, and cryogenic technology, the molecular mechanisms driving these phenomena remain unexplored. Herein, utilizing cryogenic transmission electron microscopy, we investigate the formation of ice at two different temperatures, demonstrating a size-dependent phase shift from I c to I sd . Furthermore, a relatively metastable cubic phase in I sd transitions to a hexagonal phase under electron beam radiation. This transition, facilitated by crystal defects, contrasts with perfect crystalline I c , which maintains its original phase, emphasizing the importance of defects in polymorphic phase transitions. Our findings provide novel insights on phase control during the ice growth processes and polymorphic phase transitions from the cubic-to-hexagonal phases.

The crystallographic study of two polymorphs of the industrial pyrazolone Pigment Orange 13 (P.O.13) is reported. The crystal structure of the β phase was determined using single-crystal X-ray analysis of a tiny needle. The α phase was investigated using three-dimensional electron diffraction. The electron diffraction data contain sharp Bragg reflections and strong diffuse streaks, associated with severe stacking disorder. The structure was solved by careful analysis of the diffuse scattering, and similarities of the unit-cell parameters with the β phase. The structure solution is described in detail and this provides a didactic example of solving molecular crystal structures in the presence of diffuse scattering. Several structural models were constructed and optimized by lattice-energy minimization with dispersion-corrected DFT. A four-layer model was found, which matches the electron diffraction data, including the diffuse scattering, and agrees with X-ray powder data. Additionally, five further phases of P.O.13 are described., (open access.)

O'3-Na 3 Ni 2 SbO 6 with a honeycomb cation order, as a potential cathode, presents simplified phase-transition steps and a high average voltage. To mitigate the intrinsic phase irreversibility, Mg, Zn, and Co have been introduced to displace part of the Ni, which inevitably reduces the theoretical capacity related to the Ni 2+ /Ni 3+ redox reaction. In this work, an unusual dual-site substitution is carried out to increase the P'3-O'3 structure reversibility without sacrificing the practical capacity. In addition, it is found that special stacking faults along the c -axis direction can be induced by doping to result in incomplete Sb/Ni disorder, though the honeycomb order remains in every TM (transition-metal) layer. The codoped Na 2.85 Cs 0.15 Ni 1.9 Mg 0.1 SbO 6 has a high degree of disorder, which breaks the ideal monoclinic symmetry ( C 2/ m ) and partly upgrades its structure to higher-symmetry models. Profiting from the influence of stacking disorder and doping ions on the coordination environment around Na, more gradual and smaller variations of the lattice parameters appear upon Na-ion extraction/insertion. Consequently, this cathode displays a high initial discharge capacity (120 mAh g -1 ), long-term cycling stability, and excellent rate performance (66 mAh g -1 under 10 C). These findings reveal that not only a full TM-disordered arrangement but also this incomplete stacking disorder can effectively improve the performance of a layered cathode.

PtSe 2 is one of the most promising materials for the next generation of piezoresistive sensors. However, the large-scale synthesis of homogeneous thin films with reproducible electromechanical properties is challenging due to polycrystallinity. It is shown that stacking phases other than the 1T phase become thermodynamically available at elevated temperatures that are common during synthesis. It is shown that these phases can make up a significant fraction in a polycrystalline thin film and discuss methods to characterize them, including their Seebeck coefficients. Lastly, their gauge factors, which vary strongly and heavily impact the performance of a nanoelectromechanical device are estimated., (© 2022 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Diffraction data acquired from cryocooled protein crystals often include diffraction from ice. Analysis of ice diffraction from crystals of three proteins shows that the ice formed within solvent cavities during rapid cooling is comprised of a stacking-disordered mixture of hexagonal and cubic planes, with the cubic plane fraction increasing with increasing cryoprotectant concentration and increasing cooling rate. Building on the work of Thorn and coworkers [Thorn et al. (2017), Acta Cryst. D73, 729-727], a revised metric is defined for detecting ice from deposited protein structure-factor data, and this metric is validated using full-frame diffraction data from the Integrated Resource for Reproducibility in Macromolecular Crystallography. Using this revised metric and improved algorithms, an analysis of structure-factor data from a random sample of 89 827 PDB entries collected at cryogenic temperatures indicates that roughly 16% show evidence of ice contamination, and that this fraction increases with increasing solvent content and maximum solvent-cavity size. By examining the ice diffraction-peak positions at which structure-factor perturbations are observed, it is found that roughly 25% of crystals exhibit ice with primarily hexagonal character, indicating that inadequate cooling rates and/or cryoprotectant concentrations were used, while the remaining 75% show ice with a stacking-disordered or cubic character., (open access.)

The freezing of water mostly proceeds via heterogeneous ice nucleation, a process in which an effective nucleation medium not only expedites ice crystallization but also may effectively direct the polymorph selection of ice. Here, we show that water confined within a hydrophobic slit nanopore exhibits a freezing behavior strongly distinguished from its bulk counterpart. Such a difference is reflected by a strong, non-monotonic pore-size dependence of freezing temperature but, more surprisingly, by an unexpected stacking ordering of crystallized two-dimensional ice containing just a few ice layers. In particular, confined trilayer ice is found to exclusively crystallize into a well-ordered, hexagonal stacking sequence despite the fact that nanopore exerts no explicit constraint on stacking order. The absence of cubic stacking sequence is found to be originated from the intrinsically lower thermodynamic stability of cubic ice over hexagonal ice at the interface, which contrasts sharply the nearly degenerated stability of bulk hexagonal and cubic ices. Detailed examination clearly reveals that the divergence is attributed to the inherent difference between the two ice polymorphs in their surface phonon modes, which is further found to generically occur at both hydrophobic and hydrophilic surfaces.

Ice formation within protein crystals is a major obstacle to the cryocrystallographic study of protein structure, and has limited studies of how the structural ensemble of a protein evolves with temperature in the biophysically interesting range from ∼260 K to the protein-solvent glass transition near 200 K. Using protein crystals with solvent cavities as large as ∼70 Å, time-resolved X-ray diffraction was used to study the response of protein and internal solvent during rapid cooling. Solvent nanoconfinement suppresses freezing temperatures and ice-nucleation rates so that ice-free, low-mosaicity diffraction data can be reliably collected down to 200 K without the use of cryoprotectants. Hexagonal ice (I h ) forms in external solvent, but internal crystal solvent forms stacking-disordered ice (I sd ) with a near-random stacking of cubic and hexagonal planes. Analysis of powder diffraction from internal ice and single-crystal diffraction from the host protein structure shows that the maximum crystallizable solvent fraction decreases with decreasing crystal solvent-cavity size, and that an ∼6 Å thick layer of solvent adjacent to the protein surface cannot crystallize. These results establish protein crystals as excellent model systems for the study of nanoconfined solvent. By combining fast cooling, intense X-ray beams and fast X-ray detectors, complete structural data sets for high-value targets, including membrane proteins and large complexes, may be collected at ∼220-240 K that have much lower mosaicities and comparable B factors, and that may allow more confident identification of ligand binding than in current cryocrystallographic practice.

There is a growing realization that the presence of stacking disorder in ice I strongly influences its physical and chemical properties. Using Raman spectroscopy, we gain new fundamental insights into the spectroscopic properties of ice. We show that stacking disorder can be detected and quantified by comparing the spectra of stacking disordered ice with spectra of the "ordinary" hexagonal ice Ih. The spectral signature of stacking disorder is thought to arise from a greater structural diversity on the local length scale, vibrational modes that appear due to the lower-symmetry environments, and a strengthening of the covalent bonds. Our findings are compared to results from diffraction and calorimetry, and we discuss the advantages and disadvantages of the three techniques with respect to detecting stacking disorder in ice I. Apart from characterizing stacking disordered ice in the research lab, our new method is perfectly suited for remote or telescopic applications aiming at the identification of stacking disordered ice in nature.