Influence of Vacancies in Manganese Hexacyanoferrate Cathode for Organic Na‐Ion Batteries: A Structural Perspective

Manganese hexacyanoferrates (MnHCF) are promising positive electrode materials for non-aqueous batteries, including Na-ion batteries, due to their large specific capacity (>130 mAh g$^{–1}$), high discharge potential and sustainability. Typically, the electrochemical reaction of MnHCF associates with phase and structural changes, due to the Jahn-Teller (JT) distortion of Mn sites upon the charge process. To understand the effect of the MnHCF structure on its electrochemical performance, two MnHCF materials with different vacancies content are investigated herein. The electrochemical results show that the sample with lower vacancy content (4 %) exhibits relatively higher capacity retention of 99.1 % and 92.6 % at 2$^{nd}$ and 10$^{th}$ cycles, respectively, with respect to 97.4 % and 79.3 % in sample with higher vacancy content (11 %). Ex-situ X-ray absorption spectroscopy (XAS) and ex situ X-ray diffraction (XRD) characterization results show that a weaker cooperative JT-distortion effect and relatively smaller crystal structure modification occurred for the material with lower vacancies, which explains the better electrochemical performance in cycled electrodes

Titania Thin Film Coated Glass for Simultaneous Ammonia Degradation and UV Light Blocking Layer in Photovoltaics

In this work, we have investigated the potential dual application of TiO2 thin films as a photocatalyst for ammonia degradation, and as a UV light blocking layer in c-Si photovoltaics. For this purpose, we deposited a series of TiO2 thin films on a glass substrate by reactive magnetron sputtering and analysed the influence of the deposition parameters (O2/Ar working gas content and pressure) on the structural, optical and photocatalytic properties. All samples are nanocrystalline anatase TiO2 and have a uniform surface (RMS roughness < 5 nm) in a wide range of magnetron sputtering deposition parameters. They are transparent in the Vis/NIR spectral range and strongly absorb light in the UV range above the optical bandgap energy (3.3 eV), which makes them suitable for the use as UV blocking layers and photocatalysts. The photocatalytic properties were studied in a mini-photocatalytic wind tunnel reactor by examining ammonia degradation. A kinetic study was performed to estimate the reaction rate constants for all samples. The intrinsic reaction rate constant confirmed the crucial role of surface morphology in ammonia decomposition efficiency

Lu-, Sm-, and Gd-Doped Ceria: A Comparative Approach to Their Structural Properties

A room temperature structural study has been performed through the whole compositional range of the (Ce1-xLux)O2-x/2 system by synchrotron X-ray diffraction and \u3bc-Raman spectroscopy. Samples were synthesized by thermal treatment in air at 1373 K of coprecipitated mixed oxalates. A CeO2-based solid solution with a fluorite-type structure (F) was found to be stable up to x = 0.4, while at higher Lu content a (F + C) biphasic region was observed, with C being the cubic atomic arrangement typical of sesquioxides of the heaviest rare earths. A comparative approach including also results deriving from other (Ce1-xREx)O2-x/2 systems (RE 61 Gd and Sm) allowed us to conclude that the compositional extent of the F solid solution is a complex function of RE3+ size and RE compressibility. On this basis, the dependence of ionic conductivity on the RE identity was interpreted as related both to the Ce4+/RE3+ size closeness and to RE compressibility. Ce4+/RE3+ dimensional issues were also revealed to rule the appearance of the hybrid structure observed in the two aforementioned systems, consisting of the intimate intergrowth of C microdomains within the F-based host lattice. Moreover, a more extended definition of F-based solid solution, including also the hybrid structure, is formulated; the latter is meant as a modification of the former, occurring when mainly RE-vacancy aggregates are incorporated into the host lattice in spite of isolated RE ions. By \u3bc-Raman spectroscopy it was possible to demonstrate that the mechanism of oxygen vacancy formation is common to all the systems studied, provided that the structure of the F-based solid solution, also including the hybrid structure, is retained

In situ reaction furnace for real-time XRD studies

The new furnace at the Materials Characterization by X-ray Diffraction beamline at Elettra has been designed for powder diffraction measurements at high temperature (up to 1373 K at the present state). Around the measurement region the geometry of the radiative heating element assures a negligible temperature gradient along the capillary and can accommodate either powder samples in capillary or small flat samples. A double capillary holder allows flow-through of gas in the inner sample capillary while the outer one serves as the reaction chamber. The furnace is coupled to a translating curved imaging-plate detector, allowing the collection of diffraction patterns up to 2[theta] [asymptotically equal to] 130°

Tuning the growth mode of nanowires via the interaction among seeds, substrates and beam fluxes

The growth mechanism of semiconductor nanowires is still an argument of high interest, and it is becoming clearer, investigation after investigation, that simple pictures fail to describe the complex behaviors observed under different growth conditions. We report here on the growth of semiconductor nanowires, maintaining control over the chemical composition and the physical state of the metallic seeds, and tuning the growth mechanism by varying the growth conditions. We focused on Au-assisted ZnSe nanowires grown by molecular beam epitaxy on GaAs(111)B substrates. We show that at sufficiently high temperatures, the Au seed is strongly affected by the interaction with the substrate and that nanowire growth can occur through two different mechanisms, which have a strong impact on the nanowire\u2019s morphology and crystal quality. In particular, ZnSe NWs may exhibit either a uniformly oriented, straight morphology when the nanoparticle seed is liquid, or a kinked, worm-like shape when the nanoparticle seed is switched to a solid phase. This switch, which tunes the nanowire growth mechanism, is achieved by controlling the Zn-to-Se beam pressure ratio at the Au-seed surface. Our results allow a deeper understanding of particle-assisted nanowire growth, and an accurate control of nanowire morphology via the control of the growth mechanism

A novel method for the evaluation of the Rare Earth (RE) coordination number in RE-doped ceria through Raman spectroscopy

A set of nine samples with nominal composition Ce0.5RE0.5O1.75 (RE \ue2\u89\ua1 Dy-Lu, Sm, Gd and Y) has been used to develop a novel method based on Raman spectroscopy, useful to evaluate the RE coordination number within the fluorite-type structure (F) of the CeO2-based solid solution. The RE coordination number is a crucial indicator of defects aggregation in doped ceria, and thus of the drop in ionic conductivity observed even well below the compositional limit of the F structure. The method has been tested on several Ce1 \ue2\u88\u92 xRExO2 \ue2\u88\u92 x/2 compositions (RE \ue2\u89\ua1 Sm, Gd and Lu, 0.1 \ue2\u89\ua4 x \ue2\u89\ua4 0.4); the obtained results are compared to literature data deriving from EXAFS spectroscopy, and advantages and criticisms of the method are thoroughly discussed. Samples were prepared by a coprecipitation method, their cationic composition was checked by SEM-EDS and their structural features were analyzed by room temperature synchrotron powder x-ray diffraction

Aging Mechanism of Mn-Based Prussian Blue Cathode Material by Synchrotron 2D X-ray Fluorescence

The aging mechanism of 10% and 30% nickel-substituted manganese hexacyanoferrate cathode material in aqueous zinc-ion batteries has been explored through the advanced synchrotron-based two-dimensional X-ray fluorescence technique. Thanks to the two-dimension modality, not only were the metal concentration dynamics throughout the entire electrodes followed during the aging process, but their spatial distribution was also revealed, suggesting the route of the material transformation. The dissolution of Mn and Ni, as well as the penetration of Zn inside the framework were detected, while the Mn aggregations were found outside the hexacyanoferrate framework. Additionally, the possibility of conducting X-ray absorption spectroscopy measurements on the regions of interest made it possible to explore the chemical state of each metal, and furthermore, synchrotron-based powder X-ray diffraction demonstrated the gradual structural modification in 30% Ni-containing sample series in terms of the different phase formation

Structural features of Sm- and Gd-doped ceria studied by synchrotron X-ray diffraction and -raman spectroscopy

A structural study of Sm- and Gd-doped ceria was performed with the aim to clarify some unexplained structural features. (Ce1-xREx)O2-x/2 samples (RE Sm, Gd; x = 0, 0.1,..., 1) were prepared by coprecipitation of mixed oxalates and subsequent thermal treatment at 1473, 1173, or 1073 K in air; they were then analyzed at room temperature both by synchrotron X-ray diffraction and \u3bc-Raman spectroscopy. Two structural models were adopted to fit the experimental data, namely, a fluoritic one, resembling the CeO2 structure at low RE content, and a hybrid one at higher RE content, intermediate between the CeO2 and the RE2O3 structures. Two main transitions were detected along the compositional range: (a) an RE-dependent transition at the boundary between the fluoritic and the hybrid regions, of a chemical nature; (b) an RE-independent transition within the hybrid region at 0.5, having a purely geometrical nature. The presence of two finely interlaced F- and C-based structures within the hybrid region was confirmed, and hints of their composition were obtained by \u3bc-Raman spectroscopy. The obtained results indicate a possible explanation for the non-Vegard behavioral trend of the cell parameters

Yb-doped Gd2O2CO3: Structure, microstructure, thermal and magnetic behaviour

Structural and microstructural features, as well as thermal and magnetic properties of Yb-doped Gd2O2CO3, were investigated with the aim to clarify the location and the oxidation state of Yb within the structure, and its role in driving the extent of the (Gd1-xYbx)2O2CO3 solid solution. Yb is found in the 3+ oxidation state and it enters the structure only at the rare earth atomic site; the solubility limit results to be located in the close vicinity of x=0.25, and thermal analyses reveal a linear decrease of the decomposition temperature with increasing the Yb amount, in agreement with literature data. The structural analysis allows to exclude longrange clusterization of Yb and Gd, since both rare earths randomly distribute over the 4f atomic position, but relying on the results of the microstructural analysis, the presence of compositional inhomogenities at the local scale cannot be excluded