RESUMEN
This study focuses on the cation intercalation of structurally unique compounds synthesized from the partial dehydration and deprotonation of coordinated water molecules in hydrous materials. Partial dehydration can potentially result in hydrous materials with a porous nature, which maintains the parent structure of the material, and deprotonation causes oxidation in the hydrous materials. Li-intercalation experiments were conducted on the hydrous iron(II) phosphate mineral, vivianite (Fe2+3(PO4)2·8H2O), and its oxidized and partially dehydrated product, santabarbaraite. Vivianite comprises two-dimensional Fe3(PO4)2 sheets and coordinated water molecules. The oxidation progress of the Fe2+ of vivianite increased cathodic capacities up to 156 mA h g-1. The Li-intercalation reaction rate increased significantly owing to dehydration because the partial dehydration of vivianite created structural space for the diffusion of Li+. Furthermore, X-ray diffraction measurements revealed that Li intercalation did not cause the formation of byproducts.
RESUMEN
Ice exhibits extraordinary structural variety in its polymorphic structures. The existence of a new form of diversity in ice polymorphism has recently been debated in both experimental and theoretical studies, questioning whether hydrogen-disordered ice can transform into multiple hydrogen-ordered phases, contrary to the known one-to-one correspondence between disordered ice and its ordered phase. Here, we report a high-pressure phase, ice XIX, which is a second hydrogen-partially-ordered phase of ice VI. We demonstrate that disordered ice undergoes different manners of hydrogen ordering, which are thermodynamically controlled by pressure in the case of ice VI. Such multiplicity can appear in all disordered ice, and it widely provides a research approach to deepen our knowledge, for example of the crucial issues of ice: the centrosymmetry of hydrogen-ordered configurations and potentially induced (anti-)ferroelectricity. Ultimately, this research opens up the possibility of completing the phase diagram of ice.
RESUMEN
Water freezes below 0 °C at ambient pressure ordinarily to ice Ih, with hexagonal stacking sequence. Under certain conditions, ice with a cubic stacking sequence can also be formed, but ideal ice Ic without stacking-disorder has never been formed until recently. Here we demonstrate a route to obtain ice Ic without stacking-disorder by degassing hydrogen from the high-pressure form of hydrogen hydrate, C2, which has a host framework isostructural with ice Ic. The stacking-disorder free ice Ic is formed from C2 via an intermediate amorphous or nano-crystalline form under decompression, unlike the direct transformations occurring in ice XVI from neon hydrate, or ice XVII from hydrogen hydrate. The obtained ice Ic shows remarkable thermal stability, until the phase transition to ice Ih at 250 K, originating from the lack of dislocations. This discovery of ideal ice Ic will promote understanding of the role of stacking-disorder on the physical properties of ice as a counter end-member of ice Ih.
RESUMEN
We present reactions of size-selected free silicon oxide cluster anions, SinOm(-) (n = 3-7, 2n - 1 ≤ m ≤ 2n + 2), with a CO gas. Adsorption of CO on SinOm(-) is observed as a major reaction channel. The rate constant of the adsorption reaction is high for the oxygen-rich clusters with m ≥ 2n + 1, whereas almost no reaction product is observed for m ≤ 2n. DFT calculations revealed that a pair of dangling O atoms on 4-fold-coordinated Si atoms plays a key role, which is the adsorption site of CO on SinOm(-). Bond formation between CO and one of the dangling O atoms is associated with electron transfer from the CO molecule to the other dangling O atom. The present findings give molecular-level insights into adsorption of CO molecules on silicates in the interstellar environment.
