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Abstract: With the potential of delivering reversible capacities of up to 300 mAh/g, Li-rich transition metal oxides hold great promise as cathode materials for future Li-ion batteries. However, a cohesive synthesis-structure-electrochemistry relationship is still lacking for these materials, which impedes progress in the field. This work investigates how and why different synthesis routes, specifically solid-state and modified Pechini sol-gel methods, affect the properties of Li2MnO3, a compositionally simple member of this material system. Through a comprehensive investigation of the syn-thesis mechanism along with crystallographic, morphological and electrochemical characterization, the effects of different synthesis routes were found to predominantly influence the degree of stacking faults and particle morphology. That is, the modified Pechini method produced isotropic spherical particles with approx. 57% faulting and the solid state samples possessed heterogeneous morphology with approx. 43% faulting probability. Inevitably, these differences lead to variations in electrochemical performance. This study accentuates the importance of understanding how syn-thesis affects the electrochemistry of these materials, which is critical considering the crystallographic and electrochemical complexities of the class of materials more generally. The methodology employed here is extendable to studying synthesis-property relationships of other compositionally complex Li-rich layered oxide systems.

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Abstract: By tuning the tolerance factor, $t$, of the Ruddlesden--Popper oxide Ca$_2$MnO$_4$ through isovalent substitutions we show that the uniaxial coefficient of linear thermal expansion (CLTE) of these systems can be systematically changed through large negative to positive values. High-resolution X-ray diffraction measurements show that the magnitude of uniaxial negative thermal expansion (NTE) increases as $t$ decreases across the stability window of the NTE phase. Transitions to phases with positive thermal expansion (PTE) are found to occur at both the high-$t$ and low-$t$ limits of stability. First-principles calculations demonstrate that reducing $t$ enhances the contribution to thermal expansion from the lowest frequency phonons, which have the character of octahedral tilts and have negative mode Gr\"uneisen parameter components along the NTE axis. By tuning $t$ to the lower edge of the NTE phase stability window, we are hence able to maximise the amplitudes of these vibrations and thereby maximise NTE with a CLTE of -8.1~ppm/K at 125~K. We also illustrate, at the other end of the phase diagram, that an enhancement in compliance of these materials associated with the rotational instability provides another mechanism by which NTE could be yet further enhanced in this and related systems.

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Abstract: The efficient production of light olefins from renewable biomass is a vital and challenging target to achieve future sustainable chemical processes. Here we report a hetero-atomic MFI-type zeolite (NbAlS-1), over which aqueous solutions of γ-valerolactone (GVL), obtained from biomass-derived carbohydrates, can be quantitatively converted into butenes with a yield of >99% at ambient pressure under continuous flow conditions. NbAlS-1 incorporates simultaneously niobium(v) and aluminium(iii) centres into the framework and thus has a desirable distribution of Lewis and Brønsted acid sites with optimal strength. Synchrotron X-ray diffraction and absorption spectroscopy show that there is cooperativity between Nb(v) and the Brønsted acid sites on the confined adsorption of GVL, whereas the catalytic mechanism for the conversion of the confined GVL into butenes is revealed by in situ inelastic neutron scattering, coupled with modelling. This study offers a prospect for the sustainable production of butene as a platform chemical for the manufacture of renewable materials.

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Abstract: The crystal structure of a novel cubic tin(II) silicate, Sn6SiO8 (space group F4̅3m, a = 10.40708(2) Å, and Z = 4), synthesized by microwave-assisted hydrothermal synthesis has been solved by Rietveld refinement of the powder X-ray diffraction (PXRD) data. The structure, analogous to zinc blende, comprises a face-centered-cubic array of [Sn6O8]4– anions, with Si4+ occupying half of the tetrahedral holes. The tin(II) silicate has been further characterized by variable-temperature PXRD, demonstrating stability of the structure and resistance to SnII oxidation up to ∼600 °C, when the compound begins to thermally decompose.

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Abstract: In developing a new compositae air electrode for Solid Oxide Cells (SOCs) it is essential to fully understand the phase chemistry of all components. Ruddlesden-Popper type electrodes such as Pr2NiO4+δ have previously been proposed as attractive alternatives to conventional La0·6Sr0·4Fe0·8Co0·2O3-δ/Ce1-xGdxO2-δ compositae air electrodes for both fuel cell and electrolyser modes of operation. However, Pr2NiO4+δ have been shown to have limited stability, reacting with a Ce1-xGdxO2-δ interlayer to form a Ce1-x-yGdxPryO2-δ (CGPO) phase of unknown stoichiometry. Additionally, Pr2NiO4+δ are known to decompose to Pr4Ni3O10 ± δ under certain conditions. In this work detailed understanding of the chemical reaction between Pr2NiO4+δ and Ce0.9Gd0.1O2-δ (CGO10) under normal solid oxide cell fabrication and operating temperatures was obtained, identifying the composition of the resulting CGPO phase reaction products. It is shown that, in addition to the unreacted CGO10 present after sintering the compositae at 1100 °C for up to 12 h, a series of CGPO chemical compositions were formed with various Ce, Gd and Pr ratios depending on the relative distance of the doped ceria phases from the Pr2NiO4+δ phases. The extent of the chemical reaction was found to depend on the sintering time and the contact area of the two phases. Further thermal treatment of the resulting products under SOC air electrode operating temperature (800 °C) resulted in the initiation of Pr2NiO4+δ decomposition, forming Pr4Ni3O10 ± δ and Pr6O11 with no detectable change in the composition of previously formed Pr-substituted ceria phases. It is apparent that the Pr2NiO4+δ/CGO10 compositae is unsuitable as an air electrode, but there is evidence that the decomposition products, Pr4Ni3O10 ± δ and Ce1-x-yGdxPryO2-δ are stable and suitable candidates for SOC electrodes.