Tungsten Bronze Type Research Articles

Photocatalytic water splitting over K3Li2Ta5O15 with a C-site-filled tungsten bronze structure and influence of metal cations at C-site on photocatalytic properties

Abstract K3Li2Ta5O15 is found as a novel photocatalyst for overall water splitting under UV light irradiation. K3Li2Ta5O15 possesses a characteristic crystal structure with Li+ ions-filled C-sites in (A1)4(A2)2C4M10O30 as the general formula of a tungsten bronze type metal oxide. Most of the reported photocatalysts with a tungsten bronze structure possess empty C-sites. K6Ta10.8O30 also possesses a C-site-filled tungsten bronze structure where C-sites are partially filled by Ta5+ ions. In diffuse reflectance spectra, K6Ta10.8O30 has an absorption edge at longer wavelength than K3Li2Ta5O15. This narrower band gap of K6Ta10.8O30 than K3Li2Ta5O15 is considered to be due to the presence of Ta5+ ions at C-sites in K6Ta10.8O30. Ta5+ ions located at 9-fold coordination C-sites with totally different surrounding environment from the 6-fold coordination M-sites will form the conduction band minimum at lower potential than those located at 6-fold coordination M-sites. The optimized K3Li2Ta5O15 shows almost the same water splitting activity with the optimized K6Ta10.8O30. Thus, it is found that the conduction band formed by Ta5+ ions at C-sites is also effective for photocatalytic reaction, being similar to that formed by Ta5+ ions at M-sites.

First-principles study of strain behavior in iron-based fluorides of tungsten bronze type as cathode materials for alkali-ion batteries

<b>First-principles study of strain behavior in iron-based fluorides of tungsten bronze type as cathode materials for alkali-ion batteries</b>

Structural and Dielectric Properties of RE3+, B3+ co-doped (RE3+=Sm3+, Dy3+) BaTa2O6 Tetragonal Tungsten Bronze-Type Ceramics

In this paper, the effect of boron doping on dielectric properties was investigated using BaTa2O6:xSm3+, yB3+ (x=5 mol%, y= 0, 5, 15, 30, 50, 70, 100 mol%) and BaTa2O6:xDy3+, yB3+ (x=10 mol%, y= 0, 5, 15, 30, 50, 70, 100 mol%) tungsten bronze ceramics fabricated by the conventional solid-state synthesis. XRD (X-ray diffraction) results revealed a single BaTa2O6 phase with space group P4/mbm (127) for both series. Additionally, in both series, there was an increase in crystallite sizes and cell parameters with increasing B3+ concentration. SEM (scanning electron microscopy) examinations indicated that the increase of boron promoted grain growth and grain elongation. In impedance results, in both series, increasing boron concentration up to 100 mol% increased the dielectric constant. Moreover, the presence of boron was associated with a relaxing transition in the B-site substitution of RE3+ (RE=Sm, Dy) ions and a contribution to the dielectric permittivity, while the increase in tetragonality or c/a ratio for both series was ascribed to the increase in the ferroelectric Curie temperature. In both series, a decrease in dielectric loss (tan δ) occurred, which was explained by the increasing sintering temperature effect with increasing boron, reducing the mobility of oxygen vacancies.

A novel Ba4(La1/5Pr1/5Nd1/5Sm1/5Eu1/5)28/3Ti18O54 high-entropy microwave dielectric ceramic with tungsten bronze-type and high-permittivity

Ba4(La1/5Pr1/5Nd1/5Sm1/5Eu1/5)28/3Ti18O54 (BLPNSET) high-entropy microwave dielectric ceramic was designed and synthesized utilizing solid-state reaction route. Single-phase tungsten bronze-type BLPNSET ceramic with Pbnm space group achieved over the sintering temperature of 1350–1500 °C verified by X-ray diffraction, Raman scattering spectroscopy, and Rietveld refinement. The dielectric characteristics were highly correlated with density, polarizability, packing fraction, and tolerance factor. The exploration of infrared reflectance (IR) spectrum for BLPNSET ceramic indicated that infrared vibrational modes associated with the A-site cation translation at low frequencies provided the majority dielectric contribution. The optimum microwave dielectric characteristics with a high-permittivity (εr = 85.34), a high-quality factor (Q×f =10,456 GHz), and a TCF = +26.8 ppm/°C were obtained in BLPNSET ceramic sintered at 1400 °C. This study provided a paradigm for tuning of dielectric characteristics of tungsten bronze-type ceramic via high-entropy strategy.

Unveiling the role of ZrO2 doping in Sr2SmTi2Nb3O15 ceramics: From structural study to dielectric enhancement

Solid-state processing was used to synthesize tungsten bronze type (TTB) solid solutions, specifically Sr2Sm(Ti1-xZrx)2Nb3O15 with x values of 0, 0.2, 0.3, and 0.4. The study examined the crystalline structure, optical properties, morphology, and electrical and dielectric characteristics of these compounds. X-ray diffraction revealed a tetragonal structure (space group P4bm). Scanning electron microscopy showed significant sample densification with grain sizes decreasing from 6.19 μm to 2.78 μm. Dielectric measurements indicated that the dielectric constant varied from 150 for x = 0 to 567.24 for x = 0.2, then decreased to 380.88 for x = 0.4, with the x = 0.3 compound having the lowest dielectric loss. The Curie temperature (Tc) decreased from 332 °C to 248.5 °C with increasing Zr content, corresponding with a reduction in grain size. The energy gap (Eg) narrowed from 2.914 eV to 2.714 eV as Zr content increased. AC conductivity increased with temperature and frequency. Electrical conductivity followed Jonscher's power law, with activation energies decreasing from 1.54 eV to 0.87 eV, explained by the small polaron tunneling (NSPT) model.

High performance Pt/Nb2W3O14 catalyst for glycerol valorization to 1,3-propanediol

Glycerol hydrogenolysis to 1,3-propanediol (1,3-PDO) is of significance in promoting the biomass valorization. To achieve the efficient conversion, the selective activation of the secondary C–O bonds in the glycerol is vital. In this work, we comparatively investigated the catalytic performances of Pt/Nb2W3O14 catalyst for glycerol hydrogenolysis controlled at the reacting conditions of 140 °C and 40 bar. Compared to Pt/WO3 and Pt/NbOx, the space–time yield (STY) of 1,3-PDO over Pt/Nb2W3O14 catalyst can be improved by a factor of 13, reaching 596.4 mg gcat−1 h−1. The cation ordering of Nb and W on atomic-scale were fully synergized their unique advantages, showing preferential adsorption of the secondary C–O bond under in-situ DRIFTS tracking. The prepared Nb2W3O14 is a tetragonal tungsten bronze (TTB) type complex oxides which can effectively promote the dispersion and reduction of Pt nanoparticles. Such strong interaction between Nb2W3O14 and Pt can coordinate the precise adsorption and activation of the secondary C–O bond, simultaneously triggering subsequent hydrogenation. Pt/Nb2W3O14 affords an ultrahigh activity in glycerol hydrogenolysis to produce 1,3-PDO, tripling the record productivity that was previously reported of these Pt-W based catalysts. This study reported the development of highly synergistic catalyst based on efficient and selective activation of the secondary C–O bond, which can be extended to catalyst design for other biomass valorization.

Novel synthesis of aluminum hydroxyfluorides AlFx(OH)3-x and application in E-1-chloro-3,3,3-trifluoropropene isomerization

A facile, safe, and environmentally friendly preparation method is described for the synthesis of AlFx(OH)3-x by the activation of γ-Al2O3 using HCFO-1233zd(E) under various temperatures. Comprehensive characterization techniques including XRD, XPS, N2 sorption, SEM, TEM, 27Al MAS NMR, FTIR, and py-IR were employed, revealing that at lower temperatures such as 275 °C and 300 °C, the synthesis yielded AlF(OH)2, while at higher temperatures like 350 °C and 375 °C, pyrochlore AlF1.5(OH)1.5 and metastable hexagonal tungsten bronze-type (HTB) β-AlF3 were formed, with α-AlF3 detected at 325 °C. Notably, a significant quantity of AlF(OH)2 can be obtained at 325 °C within a specific time frame. This amorphous phase exhibits weak Lewis acid sites and a lower acid density, rendering it significantly more effective in the isomerization of HCFO-1233zd(E) compared to strong Lewis acid catalysts such as AlF1.5(OH)1.5 and β-AlF3, which could promote coke formation, leading to catalyst deactivation. Moreover, due to its limited further fluorination at 290 °C, the optimal catalyst exhibits prolonged lifespan and high efficiency in HCFO-1233zd(E) isomerization.

Narrow-Band Deep-Blue Emission and Superior Thermal Stability of Fluoroaluminate Phosphor Based on Tungsten Bronze-Type Mineral Structure.

Screening novel narrow-band phosphors inspired by natural mineral structures is urgently demanded for improving the performance of phosphor-converted light-emitting diodes. In this work, a novel narrow-band deep-blue-emitting tungsten bronze-type KCaAl2F9:Eu2+ phosphor with superior thermal stability is successfully synthesized. Structural analysis shows that the representative KCaAl2F9:0.013Eu2+ phosphor crystallizes in an orthorhombic space group C2221 with a rigid network. The rigid [AlF6]3- octahedrons are linked together by sharing corners to build endless [AlF6]3-∞ chains, further stacking with each other in a highly cross-linked way to establish the rigid network of the KCaAl2F9 host. Benefiting from the rigid microenvironment, the developed phosphor not only shows a narrow-band deep-blue emission with a full width at half maximum of 45 nm and a high color purity of 92%, but it also exhibits the superior thermal stability with an emission loss of only 10% at 423 K, demonstrating its application potential in bridging the deep-blue spectral cavity toward sunlight-like full-spectrum lighting. In addition, the concentration/temperature quenching behaviors of KCaAl2F9:Eu2+ phosphor are systematically investigated. By revealing the specific structure-property relationship of tungsten bronze-type KCaAl2F9:Eu2+ phosphor, the present study provides a significant guide for identifying the novel narrow-band deep-blue-emitting component applicable to full-spectrum warm white light-emitting diode devices.

Energy storage properties and transparency in (Ba0.6Sr0.4)1‐1.5xBixTi1‐x(Mg1/3Nb2/3)xO3 ceramics

AbstractFully densified (transparent) ceramic with small grain size is highly desired to improve the field breakdown strength (BDS) and its scattering. Sintering behavior, microstructural evolution, electric, dielectric, and energy storage properties of (Ba0.6Sr0.4)1‐1.5xBixTi1‐x(Mg1/3Nb2/3)xO3 (x = .04–.10) ceramics have been studied in this paper. Phase pure cubic perovskite is observed for the x = .04 composition. Nb‐rich tungsten bronze type and Ti‐rich barium titanate secondary phases are present in the x &gt; .05 compositions. A multiphasic transparent ferroelectric ceramic with ∼74.2% (780 nm) transmittance and a high refractive index of ∼2.3 within the visible region could be successfully obtained for the x = .10 composition by traditional ceramic process. The x = .09 composition demonstrates good energy storage performance (recoverable energy density Wrec = 3.74J/cm3, efficiency η = 77% and BDS = 390kV/cm) with extremely low scattering in BDS, suggesting potential application in large sized energy storage capacitor.

Effect of M (M = Mn or Mg) ion doping on microstructure and dielectric properties of Ba4Nd9.33Ti17.5-xSn0.5MxO54 ceramics prepared by sol-gel method

The changing trends of Ba4Nd9.33Ti17.5-xSn0.5MxO54 (BNST-xM) ceramic dielectric properties and microstructure were investigated by substituting two types of metal ions M (M = Mn, Mg) for Ti4+ at B-site. X-ray diffractometer (XRD) results show that M2+ are successfully formed as a single tungsten-bronze type structured phase, except that x is equal to 1.25. It can be seen from the scanning electron microscope (SEM) that the rise of the ion doping amount gradually increases the defects, and the crystal shape gradually changes from slender columnar to short and rounded. M2+ substitutions greatly impacted the suppression of oxygen vacancies and Ti3+ generation in BNST-xM ceramic, particularly Mg2+, which was confirmed by X-ray photoelectron spectrometer (XPS) results. The incorporation of M2+ ions into the system increased the Q·f value while reducing the dielectric constant of the ceramics. Mg2+ can improve the material's Q·f value, and the doping of Mn2+ will lessen the frequency temperature coefficient of the material more. When the doping amount x of Mg2+ was 0.25, the system had the best dielectric properties: ε = 64.4, Q·f value = 10,170 GHz, and τ = 25 ppm/°C.

Structure and relaxor ferroelectric behavior of the novel tungsten bronze type ceramic Sr5BiTi3Nb7O30

This paper reports a novel lead-free tungsten bronze type ceramic, Sr5BiTi3Nb7O30, prepared by a conventional high-temperature solid-state reaction route. The crystal structure identified using synchrotron x-ray diffraction data and Raman spectroscopy for Sr5BiTi3Nb7O30 could be described as an average structure with the centrosymmetric space group P4/mbm and a local non-centrosymmetric structure at room temperature. In the second-harmonic generation measurement, the Sr5BiTi3Nb7O30 compound exhibits second-order nonlinear optical behavior, which suggests the material is ferroelectric. Temperature dependence of the dielectric permittivity indicates that the dielectric anomaly in Sr5BiTi3Nb7O30, associated with the disorder on the A and B sites, results in strong frequency dispersion with a low phase-transition temperature. A macroscopic and phenomenological statistical model was employed to describe the temperature dependence of the dielectric responses of Sr5BiTi3Nb7O30 and Sr6Ti2Nb8O30. The calculated sizes of polar nanoregions for both compounds imply structural disorder induced by A and B sites, giving rise to a more diffuse ferroelectric transition for Sr5BiTi3Nb7O30. The smaller polar nanoregions with smaller electrical dipole moments can be activated at lower temperatures, leading to Sr5BiTi3Nb7O30 having a lower Tm (∼260 K) than other tungsten bronze type ferroelectrics. This work charts a promising feasible route to the development of improved relaxor ferroelectrics in tungsten bronze type oxides.

Correlation between crystal structure and dielectric response for orthorhombic tungsten bronze ceramics Ba4(Nd1-xSmx)28/3(Ti0.95Zr0.05)18O54

Ba4(Nd1-xSmx)28/3(Ti0,95Zr0,05)18O54 ceramics with (x = 0; 0.2; 0.4; 0.8 and 1) were synthesized by solid method at 1250 °C for 10 h. The effects of Nd/Sm ratio on the structure and dielectric behavior were studied by changing the value of x. The study of Ba/RE order with (RE = Nd and Sm) in the solid solution Ba4(Nd1-xSmx)28/3(Ti0,95Zr0,05)18O54 was realized by X-ray diffraction. The crystal structure of these phases belongs to the tungsten bronze type, which is constructed on the basis of the (3x3) Ti/ZrO6 octahedron more than (2x2) (orthorhombic symmetry, space group Pnma, a ≈22.3 Å, b ≈ 7.67 Å, c ≈ 12.1 Å). A structural model has been established, corresponding to an order within the structure. The model of formula [Ba4]A2[Ba2-a(Nd1-xSmx)1.33+b□c]A1'[(Nd1-xSmx)8-d□d]A1(Ti0.95Zr0.05)18O54, corresponds to a model associated to infinite perovskite rows parallels to the Oy axis, constructed on the basis of the octahedron (3x3) Ti/ZrO6. Scanning electron microscopy (SEM) has showed that Ba4(Nd1-xSmx)28/3(Ti0,95Zr0,05)18O54 ceramics have a typical columnar grain, which indicates that the phase structure of tungsten bronze exists in the x range and all samples show a dense microstructure. The average grain size ranges from 1.179 to 0.912 μm. The dielectric properties were studied by complex impedance spectroscopy in the temperature range from 30 °C to 800 °C where an anomaly was observed in a few compositions characterized by a maximum of the dielectric permittivity that shifts with increasing frequency at higher temperatures. The presence of a strong dispersion over a wide range of temperatures, is probably related to cationic disorder within the Ba4(Nd1-xSmx)28/3(Ti0,95Zr0,05)18O54 structure.

On the Arrangement of Pentagonal Columns in Tetragonal Tungsten Bronze-Type Nb18W16O93

The evaluation of HAADF-STEM images of a sample with the composition Nb18W16O93 provided new insights into its real structure. The basic structure comprises an intact octahedral framework of the tetragonal tungsten bronze (TTB) type. The partial occupation of the pentagonal tunnels (PT) by metal–oxygen strings determines the oxygen-to-metal ratio (O/ΣM with M = Nb,W). For a large area, the O/ΣM was determined to be 2.755, which is bigger than the value of Nb18W16O93, which is O/ΣM = 2.735. To a large extent, the three-fold TTB superstructure of Nb8W9O47 with a high oxygen content is present (O/ΣM = 2.765). In addition, a new four-fold TTB superstructure was found in small domains. Nb12W11O63 with an O/ΣM = 2.739 obviously accommodates part of the sample’s metal excess compared to the stable phase Nb8W9O47.

Atomic resolution imaging of cation ordering in niobium\u2013tungsten complex oxides

Energy dispersive X-ray emission imaging at atomic resolution is a powerful tool to solve order–disorder problems in complex metal oxide crystals, supplementing conventional X-ray or neutron diffraction. Here, we use this method, based on scanning transmission electron microscopy, to investigate cation ordering in ternary metal oxides 4Nb2O5·9WO3 and 2Nb2O5·7WO3, which have recently attracted attention as energy storage materials in lithium-ion batteries. Their crystal structures are a tetragonal tungsten bronze-type and its hybrid with a ReO3-type ‘block structure’, respectively. Our study reveals the presence of chemical ordering of metal ions in these materials, which have previously been assumed to be solid-solutions. In particular, we show that the two types of cations, Nb and W, are well ordered in their lattices, and that the Nb ions tend to occupy one third of the pentagonal channel sites. These results demonstrate that atomic resolution X-ray emission imaging is an effective alternative approach for the study of locally ordered crystal structures.

On the structural complexity of tetragonal tungsten bronze type niobium tungsten oxides

AbstractIn this comparative study, two samples with a slightly different oxygen : metal ratio have been characterized by various electron microscopy methods and by single‐crystal and powder X‐ray diffraction (XRD). A reasonably good fit to the experimental powder XRD patterns could be achieved by Rietveld refinement for both samples Nb8W9O47 and Nb7W10O47.5 using the structural models of Nb6.7W10.3O47 and Nb8W9O47 both obtained from X‐ray crystal structure analysis. HRTEM investigations confirm that Nb8W9O47 crystallizes as a pure phase in the well‐known threefold superstructure of the tetragonal tungsten bronze type (TTB). In contrast, a more complex real structure was found for the sample Nb7W10O47.5 with small domains of Nb4W7O31 appearing besides large ones of Nb8W9O47 and in addition extended TTB‐based areas with short‐range order only. The diffuse scattering caused by this disorder is easily detected in the electron diffraction pattern but does not affect the Rietveld refinement of the powder XRD patterns. However, on the basis of powder diffraction experiments, it is clearly possible to distinguish between the above compounds and the hypothetical, but non‐existing compound “Nb18W16O93”, a composition recently postulated for battery materials.

Resistance Switching Effect in Octahedral framework oxide

Resistive Random-Access Memories (ReRAM) are an alternative way to create new memory devices. This is physically possible due to the existence in the material, of two resistive states clearly discreditable, as a function of voltage value and polarity first parameter under control to pass from one state to another one. However, the mechanism of the resistance switching is not simple and is under debate. We present in the present chapter all the factors entering in the switching process in tetragonal tungsten bronze (TTB) type structure oxide thin films deposited by PLD technique onto MgO or STO substrates. Results show that GdK2Nb5O15 (GKN) thin films deposited on MgO and STO substrates are resistively switchable. It was found that the nature of the substrate strongly affects the resistance ratio: GKN on SRO/LSCO/MgO showed a large hysteresis compared to GKN on SRO/STO. Substrate effect and oxygen vacancy on resistance switching in GKN thin film were studied in the same experimental conditions. The study of resistance switching in the GKN/MgO and GKN/STO thin films has confirmed that for low voltages, below the threshold value of 1.3 V, the electric transport is dominated by the formation of a Schottky type barrier, which allows a minimum leakage current. Resistance switching in GKN is attributed to the oxygen vacancies migration which can be controlled by the substrate or the frequency sweep.

Synthesis of Ti(OH)OF ⋅ 0.66 H2 O in Imidazolium-based Ionic Liquids.

The influence of the cation of imidazolium‐derived ionic liquids (ILs) on a low‐temperature solution‐based synthesis of hexagonal tungsten bronze (HTB) type Ti(OH)OF ⋅ 0.66 H2O and bronze‐type TiO2(B) is investigated. The IL (Cxmim BF4) acts as solvent and also as reaction partner with respect to the decomposition of [BF4]−, releasing F−. In the present study, the chain length of the alkyl chain side groups attached to the imidazolium ring was varied (C2mim BF4 to C10mim BF4), and the obtained solids were analyzed by Powder X‐Ray diffraction (PXRD) followed by Rietveld refinement. As a main finding these analyses indicate a transformation of Ti(OH)OF ⋅ 0.66 H2O into TiO2(B), and upon prolonged reaction time finally also into anatase TiO2. Rietveld analysis suggests that when using ILs with longer alkyl chains, the conversion of Ti(OH)OF ⋅ 0.66 H2O is slower compared to syntheses performed with smaller alkyl chains. Hence, Ti(OH)OF ⋅ 0.66 H2O appears to be metastable and is stabilized by long‐chain ILs serving as surfactant attached to the crystallites’ surface. In this view, the ILs shield the nanoparticles and thus slow down the conversion into the more stable compounds. This confirms previous findings that ILs act as both, solvent and reaction medium in this reaction, thus enabling the synthesis of peculiar Ti‐oxides.

A novel photochromic ceramics with reversible luminescence modulation and light bleaching behavior: Sm3+-doped KSr2Nb5O15

A novel tetragonal tungsten bronze (TTB) type Sm3+-doped KSr2Nb5O15 (KSN-Sm) optical ceramic is fabricated by atmosphere sintering technology. A reversible photochromic effect between faint yellow and olive colors and accompanied luminescence modulation behaviour can be realized by alternating the 395 nm light irradiation and thermal treatment. The thermal stimulus model is introduced to modify the classical resonance energy transfer mechanism. The results show that the optimal luminescence modulation ratio △Rt about the red emission (601 nm) intensity amounted to 60.0 %, and the KSN-Sm ceramic exhibits excellent luminescence modulation rate and reproducibility. The colored KSN-Sm ceramic can be partly bleached by external light stimulus (620 nm), and the luminescence emission intensity can be recovered from 45 % to 84.2 %. The light bleaching efficiency is strongly dependent on the irradiation wavelength, exposure duration and irradiation dose. These discoveries pave the way to develop new luminescence materials with TTB structure.

Relationships between crystalline structure and dielectric properties in Sr 2 Sm (1-x) Nd x Ti 2 Nb 3 O 15 ceramics

In this study, tungsten-bronze type materials of Sr 2 Sm (1-x) Nd x Ti 2 Nb 3 O 15 composition (x=0; 0,25; 0,5; 0,75 and 1) were elaborated by classical solid-state reaction. The structural characterization demonstrate that these compounds present tetragonal symmetry, using two space groups P4bm (N°100) and P4/mbm (N°127) respectively. The lattice parameters are a=b≈12,2Ǻ; c≈3,8Ǻ; V≈579,0 3 Ǻ and Z=2. In this compounds, Ti and Nb cations show obvious off-center displacements along the c axis in both the Ti/Nb(1)O 6 and the Ti/Nb(2)O 6 octahedra. Besides, the unequal Ti/Nb(2)–O bonds length in the equatorial plane of Ti/Nb(2)O 6 octahedra indicates the displacement of the Ti/Nb(2) cations in the ab plane, and no displacement of the Ti/Nb(1) cations exists in the ab plane. The results show that this material has two types of octahedral, first octahedron with little deformation around the Ti1/Nb1 and the second octahedron are more distorted around the Ti2/Nb2. The measurements of permittivity and dielectric losses of the ceramic samples performed between 25°C and 700°C (100Hz to 1MHz), high dielectric constants (e r =127 ~ 194) and low dielectric losses (tan(δ) around 10 -4 at 1MHz) were found. The maximum value of the dielectric constant is obtained for x=0 (e r =194). The Curie temperature Tc decreases from 332 to 246°C as a function of the substitution of the samarium by neodymium. Detailed microstructural analysis by scanning electron microscope (SEM) and (EDS) for this compounds are also investigated.

Stabilization of a mixed iron vanadium based hexagonal tungsten bronze hydroxyfluoride HTB-(Fe0.55V0.45)F2.67(OH)0.33 as a positive electrode for lithium-ion batteries.

In our search for novel insertion compounds for Li-based batteries, we have identified a new mixed iron vanadium based Hexagonal Tungsten Bronze (HTB) type phase. Its synthesis involves two steps which consist first of preparing mixed metal hydrated fluoride Fe1.64V1.36F8(H2O)2 by a microwave assisted thermal process, followed by thermal treatment under air to obtain metastable HTB-(Fe0.55V0.45)F2.67(OH)0.33 hydroxyfluoride. 57Fe Mössbauer spectrometry demonstrates the presence of oxidation states Fe2+ and Fe3+ in Fe1.64V1.36F8(H2O)2 as opposed to only Fe3+ in HTB-(Fe0.55V0.47)F2.67(OH)0.33. Moreover, the Mössbauer spectra recorded at 77 K reveal that none of the compounds shows magnetic ordering owing to the presence of V3+ distributed over the crystallographic sites of Fe3+. Complementary X-ray spectroscopy and Rietveld refinement further confirm the successful synthesis of HTB-(Fe0.55V0.45)F2.67(OH)0.33. Electrochemically, the new HTB-(Fe0.55V0.45)F2.67(OH)0.33 shows a first discharge capacity of 181 mA h g-1 with 67% of this capacity remaining upon cycling. Unlike HTB-FeF2.66(OH)0.34, the structure remains stable after the first discharge confirming the positive effect of vanadium in the HTB network.