Optimization of hydrogen-ion storage performance of tungsten trioxide nanowires by niobium doping

The transport and storage of ions within solid state structures is a fundamental limitation for fabricate more advanced electrochemical energy storage, memristor, and electrochromic devices. Crystallographic shear structure can be induced in the tungsten bronze structures composed of corner-sharing WO6 octahedra by the addition of edge-sharing NbO6 octahedra, which might provide more storage sites and more convenient transport channels for external ions such as hydrogen ions and alkali metal ions. Here, we show that Nb2O5·15WO3 nanowires with long length-diameter ratio, smooth surface, and uniform diameter have been successfully synthesized by a simple hydrothermal method. The Nb2O5·15WO3 nanowires do exhibit more advantages over h-WO3 nanowires in electrochemical hydrogen ion storage such as smaller polarization, larger capacity(71 mAh/g, at 10C, 1C = 100 mA/g), better cycle performance (remain at 99% of the initial capacity after 200 cycles at 100C) and faster H+ diffusion kinetics. Therefore, complex niobium tungsten oxide nanowires might offer great promise for the next generation of hydrogen ion batteries.

Synthesis and Characterization of Tungsten Suboxide WnO3n−1 Nanotiles

WnO3n−1 nanotiles, with multiple stoichiometries within one nanotile, were synthesized via the chemical vapour transport method. They grow along the [010] crystallographic axis, with the thickness ranging from a few tens to a few hundreds of nm, with the lateral size up to several µm. Distinct surface corrugations, up to a few 10 nm deep appear during growth. The {102}r crystallographic shear planes indicate the WnO3n−1 stoichiometries. Within a single nanotile, six stoichiometries were detected, namely W16O47 (WO2.938), W15O44 (WO2.933), W14O41 (WO2.928), W13O38 (WO2.923), W12O35 (WO2.917), and W11O32 (WO2.909), with the last three never being reported before. The existence of oxygen vacancies within the crystallographic shear planes resulted in the observed non-zero density of states at the Fermi energy.

Shear Pleasure: The Structure, Formation, and Thermodynamics of Crystallographic Shear Phases

A renaissance of interest in crystallographic shear structures and our recent work in this remarkable class of materials inspired this review. We first summarize the geometrical aspects of shear plane formation and possible transformations in ReO3, rutile, and perovskite-based structures. Then we provide a mechanistic overview of crystallographic shear formation, plane ordering, and propagation. Next we describe the energetics of planar defect formation and interaction, equilibria between point and extended defect structures, and thermodynamic stability of shear compounds. Finally, we emphasize the remaining challenges and propose future directions in this exciting area. Expected final online publication date for the Annual Review of Materials Science, Volume 51 is July 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Superionic Lithium Intercalation through 2 nm x 2 nm Columns in the Crystallographic Shear Phase Nb18W8O69

<p>Nb₁₈W₈O₆₉ (9Nb₂O₅×8WO₃) is the tungsten-rich end-member of the Wadsley–Roth crystallographic shear (<i>cs</i>) structures within the Nb₂O₅–WO₃ series. It has the largest block size of any known, stable Wadsley–Roth phase, comprising 5 x 5 units of corner-shared MO₆ octahedra between the shear planes, giving rise to 2 nm x 2 nm blocks. Rapid lithium intercalation is observed in this new candidate battery material and ⁷Li pulsed field gradient nuclear magnetic resonance spectroscopy – measured in a battery electrode for the first time at room temperature – reveals superionic lithium conductivity with Li diffusivities at 298 K predominantly between 10^–10 and 10^–12 m²·s^–1. In addition to its promising rate capability, Nb₁₈W₈O₆₉ adds a piece to the larger picture of our understanding of high-performance Wadsley–Roth complex metal oxides.</p>

Superionic Lithium Intercalation through 2 nm x 2 nm Columns in the Crystallographic Shear Phase Nb18W8O69

<p>Nb₁₈W₈O₆₉ (9Nb₂O₅×8WO₃) is the tungsten-rich end-member of the Wadsley–Roth crystallographic shear (<i>cs</i>) structures within the Nb₂O₅–WO₃ series. It has the largest block size of any known, stable Wadsley–Roth phase, comprising 5 x 5 units of corner-shared MO₆ octahedra between the shear planes, giving rise to 2 nm x 2 nm blocks. Rapid lithium intercalation is observed in this new candidate battery material and ⁷Li pulsed field gradient nuclear magnetic resonance spectroscopy – measured in a battery electrode for the first time at room temperature – reveals superionic lithium conductivity with Li diffusivities at 298 K predominantly between 10^–10 and 10^–12 m²·s^–1. In addition to its promising rate capability, Nb₁₈W₈O₆₉ adds a piece to the larger picture of our understanding of high-performance Wadsley–Roth complex metal oxides.</p>

How Nanoscale Dislocation Reactions Govern Low- Temperature and High-Stress Creep of Ni-Base Single Crystal Superalloys

The present work investigates γ-channel dislocation reactions, which govern low-temperature (T = 750 °C) and high-stress (resolved shear stress: 300 MPa) creep of Ni-base single crystal superalloys (SX). It is well known that two dislocation families with different b-vectors are required to form planar faults, which can shear the ordered γ’-phase. However, so far, no direct mechanical and microstructural evidence has been presented which clearly proves the importance of these reactions. In the mechanical part of the present work, we perform shear creep tests and we compare the deformation behavior of two macroscopic crystallographic shear systems [ 01 1 ¯ ] ( 111 ) and [ 11 2 ¯ ] ( 111 ) . These two shear systems share the same glide plane but differ in loading direction. The [ 11 2 ¯ ] ( 111 ) shear system, where the two dislocation families required to form a planar fault ribbon experience the same resolved shear stresses, deforms significantly faster than the [ 01 1 ¯ ] ( 111 ) shear system, where only one of the two required dislocation families is strongly promoted. Diffraction contrast transmission electron microscopy (TEM) analysis identifies the dislocation reactions, which rationalize this macroscopic behavior.

Understanding the role of crystallographic shear on the electrochemical behavior of niobium oxyfluorides

The effects of shear planes in perovskitic materials have been studied in order to identify their role in the electrochemical behavior and structural evolution of Li+ intercalation hosts.