A vanadium-based oxide-phosphate-pyrophosphate framework as a 4 V electrode material for K-ion batteries

K-ion batteries (KIBs) are promising for large-scale electrical energy storage owing to the abundant resources and the electrochemical specificity of potassium. Among the positive electrode materials for KIBs, vanadium-based polyanionic materials are interesting because of their high working voltage and good structural stability which dictates the cycle life. In this study, a potassium vanadium oxide phosphate, K₆(VO)₂(V₂O₃)₂(PO₄)₄(P₂O₇), has been investigated as a 4 V class positive electrode material for non-aqueous KIBs. The material is synthesized through pyrolysis of a single metal–organic molecular precursor, K₂[(VOHPO₄)₂(C₂O₄)] at 500 °C in air. The material demonstrates a reversible extraction/insertion of 2.7 mol of potassium from/into the structure at a discharge voltage of ∼4.03 V vs. K. Operando and ex situ powder X-ray diffraction analyses reveal that the material undergoes reversible K extraction/insertion during charge/discharge via a two-phase reaction mechanism. Despite the extraction/insertion of large potassium ions, the material demonstrates an insignificant volume change of ∼1.2% during charge/discharge resulting in excellent cycling stability without capacity degradation over 100 cycles in a highly concentrated electrolyte cell. Robustness of the polyanionic framework is proved from identical XRD patterns of the pristine and cycled electrodes (after 100 cycles).

Highly pure K₆(VO)₂(V₂O₃)₂(PO₄)₄(P₂O₇), synthesized from the oxalatophosphate precursor, demonstrates a reversible potassium extraction/insertion capacity of 59 mA h g⁻¹ with a single discharge voltage plateau at 4.0 V at room temperature.     

Thermodynamic properties of successive phase transitions in Rb2ZnBr4

Heat capacity measurements have given the following transition temperatures and entropies: 0.027 J K^?1mol^?1 at 76.5 K, 0.47 J K^?1mol^?1 at 111.7 K, and 0.048 J K^?1mol^?1 at 193.6 K. These are interpreted as “lock-in”, soft-mode, and “lock-in” transitions, respectively, from comparison with analogous results for Rb₂ZnCl₄ and K₂SeO₄. The N-IC transition was located at 347 K by DTA.     

Catalytic <Emphasis Type="Italic">N</Emphasis>-Alkylation of Amines with Primary Alcohols over Halide Clusters

Piperidine was reacted with methanol under a hydrogen stream in the presence of (H₃O)₂[(W₆Cl₈)Cl₆]·6H₂O supported on silica gel. When the temperature was raised above 200 °C, the catalytic activity of the cluster appeared. Piperidine N-methylation proceeded yielding N-methylpiperidine in 95% selectivity at 350 °C. The corresponding halide clusters of niobium, molybdenum, and tantalum supported on silica gel also catalyzed the reaction. Primary alcohols such as ethanol and 1-propanol produced the corresponding N-alkyl products of piperidine; however, secondary and tertiary alcohols did not. Selective N-methylation of pyrrolidine, hexamethyleneimine, butylamine, and aniline also proceeded. Thus, the clusters catalyzed alkylation of aliphatic, alicyclic, and aromatic amines with primary alcohols. A Brønsted acid site attributable to a hydroxo ligand, which is formed on the cluster complex by thermal activation, is proposed as the active site of the catalyst.     

Holomorphic Hermite functions and ellipses

In 1990 van Eijndhoven and Meyers introduced systems of holomorphic Hermite functions and reproducing kernel Hilbert spaces associated with the systems on the complex plane. Moreover they studied the relationship between the family of all their Hilbert spaces and a class of Gelfand–Shilov functions. After that, their systems of holomorphic Hermite functions have been applied to studying quantization on the complex plane, combinatorics, and etc. On the other hand, the author recently introduced systems of holomorphic Hermite functions associated with ellipses on the complex plane. The present paper shows that their systems of holomorphic Hermite functions are determined by some cases of ellipses, and that their reproducing kernel Hilbert spaces are some cases of the Segal–Bargmann spaces determined by the Bargmann-type transforms introduced by Sjöstrand.     

Adsorption equilibrium of the mixture of EtOH and TCE on?FAU?type high silica zeolite

In this study, the adsorption equilibrium of the FAU type high silica zeolite was obtained by a gravimetric adsorption experiment device and a molecular simulation. The adsorbate used was ethanol and trichloroethylene, which are the system of azeotropic mixture.     

Measurement of spatial coherence of a copper vapour laser beam using a reversal shear interferometer

We measured the spatial coherernce of a copper vapour laser (CVL) beam with an unstable resonator by the reversal shear interferometer. By this method, we can evaluate the spatial coherence function from a single-shot measurement. The spatial coherence width was 5 mm when an unstable resonator with a magnification factor of 60 was used. Moreover we verified the result by the theoretical calculation on the basis of the passive resonator model.     

On generalized Stieltjes-Wigert and related orthogonal polynomials

The Charlier, Wall, and generalized Stieltjes-Wigert polynomials are characterized by a property involving the concept of kernel polynomials. This characterization leads to consideration of a certain functional equation satisfied by solutions of the associated Stieltjes moment problem. All distribution functions which satisfy this functional equation are found up to singular functions. This yields new distribution functions, both discrete and absolutely continuous, with respect to which generalized Stieltjes-Wigert polynomials are orthogonal.     

Thermodynamic properties of Rb2ZnCl4 associated with three phase transitions

Transitions were observed by heat capacity measurements at 74.6 K, 195.2 K, and 303 K. They are a soft mode transition (ΔH_t = 30 J mol^?1, ΔS_t = 0.42 J K^?1 mol^?1), a first-order commensurate-incommensurate transition (ΔH_t = 6.2 J mol^?1ΔS_t = 0.032 J K^?1 mol^?1), and a second-order incommensurate-normal transition, respectively.