In situ UV-Vis and ex situ IR spectroelectrochemical investigations of amorphous and crystalline electrochromic Nb2O5 films in charged/discharged states

Niobium oxide (Nb₂O₅) films and powders have been obtained via the sol-gel route from an NbCl₅ precursor. XRD spectra revealed that films with pseudohexagonal (TT-phase) and orthorhombic (T-phase) structure were formed at 500  °C and 800  °C, respectively, while at 300  °C films were amorphous. Infrared (IR) and Raman spectra of powders and films of Nb₂O₅ in different polymorphic forms were detected, and vibrational band assignments were made. Electrochromic properties of amorphous films and films with the TT-phase were established from in situ ultraviolet visible (UV-Vis) spectroelectrochemical measurements and correlated with ex situ IR transmission spectra of charged films. Ex situ IR spectra revealed that charging of amorphous films is accompanied by variations of the Nb-O stretching mode intensity, while, for films with the TT- and T-phase, splitting of the Nb₃-O stretching modes and the appearance of polaron absorption were noted with Li⁺ ion insertion. Ex situ X-ray diffraction (XRD) spectra of charged films with the TT-phase showed changes of the unit cell dimensions with charging. The influence of the polaron absorption on the ex situ near-grazing incidence angle (NGIA) IR reflection-absorption spectra of charged/discharged films is discussed in detail. Received: 21 August 1997 / Accepted: 9 October 1997     

Electrochemical and Structural Characterisation of Dip-Coated Fe/Ti Oxide Films Prepared by the Sol-Gel Route

Thin solid films of mixed Fe/Ti oxide composition (Fe/Ti molar ratios: 0.5∶1, 1∶1, 1.5∶1) have been made from Fe(NO₃)₃ alcoholic solution to which Ti(OiPr)₄ was added. Films have been deposited by the dip-coating technique and heat-treated at 300°C and 500°C. Powders of Fe/Ti oxide heat-treated at 300°C are amorphous, while powders annealed at 500°C for 40 hours transformed to mixed rutile, pseudobrookite and hematite phases. The structure of the XRD amorphous films was identified with the help of near-normal reflection absorption (6°) (IRRA) and near-grazing incidence angle (NGIA) spectroscopy. NGIA FT-IR spectra of films are characterised with a single phonon mode appearing in the spectral range 600–950 cm⁻¹ which shifts with increasing Ti concentration from 675 cm⁻¹ (Fe₂O₃) to 904 cm⁻¹ (TiO₂) thus exhibiting one-mode behavior. Electrochemical investigations made with the help of cyclic voltammetry (CV) and chronocoulometry (CPC) performed in 0.01M LiOH and in 1M LiClO₄/propylene carbonate electrolytes revealed that films are able to uptake reversibly Li⁺ ions with a charge capacity (Q) per film thickness (d) in the range 0.1–0.26 mC/cm²nm and 0.06 mC/cm²nm, respectively. The temperature at which the films were prepared alters the rate of Li⁺ insertion which is faster for less compact films obtained at 300°C. In situ UV-VIS spectroelectrochemical measurements revealed that Fe/Ti oxide films bleached in the UV spectral region (300 nm<λ<450 nm) and colored in the VIS spectral region (450 nm<λ<800 nm), thus exhibiting mixed anodic and cathodic electrochromism.     

Synthesis, Crystal Structure, and IR Spectroscopic Characterization of 1,6-Hexanediammonium Dihydrogendecavanadate

 Anhydrous 1,6-hexanediammonium dihydrogendecavanadate ((HdaH₂)₂H₂V₁₀O₂₈, 1) was prepared by reaction of V₂O₅ with 1,6-hexanediamine in aqueous solution. The crystal structure of 1 was determined, and the proton positions in the H₂V₁₀O₂₈ ⁴⁻ anion were calculated by the bond length/bond number method. The protons are bound to the centrosymmetrically oriented μ–OV₃ groups of the decavanadate anion. Based on the analysis of IR spectra of 1 prepared from H₂O and D₂O, the absorption band at 871 cm⁻¹ can be attributed to δ(V–O_b–H) vibrations.     

Effects of lithium insertion and deinsertion into V2O5 thin films: Optical,structural, and absorption properties

The lithiated/delithiated vanadium pentoxide films deposited by sol‐gel spin coating on indium tin oxide–coated glass substrates were analyzed by sputter‐induced photon spectroscopy, X‐ray diffraction, and optical absorption techniques. First, it is shown that the crystalline structure of V₂O₅ after intercalation remains practically unchanged. Particularly, in the optical spectra during 5 keV Kr⁺ ion bombardment of clean, intercalated, and deintercalated V₂O₅ films, a series of sharp lines and unexpected continuum radiation were observed and well explained. It is also demonstrated that the intercalation and deintercalation of lithium have strong influences on various characteristics of pentoxide vanadium. The interpretations of the obtained results in the 3 experiments—X‐ray diffraction, sputter‐induced photon spectroscopy, and optical absorption techniques—are coherent and complement each other.     

Dehydration-induced changes in the vibrational states of dioptase Cu6Si6O18·6H2O

This paper reports on the results of temperature studies (20–880°C) of the IR absorption spectra of dioptase crystals in the range 50–4000 cm⁻¹. During the dehydration of dioptase the state of water changes as follows: (1) initial state, (2) intermediate state with damped external vibrations of H₂O, (3) isolated water molecules with new hydrogen bonds, (4) formation of hydroxyls. The bands of the external virations of H₂O (1) vanish in state (2) because of the formation of vacancies in the six-membered water rings. The frequencies of the translation vibrations of 6H₂O in initial dioptase are close to those in liquid water: 169–170 and 277–290 cm⁻¹. A factor-group analysis of the dioptase vibrations in the space group C _3i ² is performed. All IR active vibrations 23A_u+23E_u are described. The thirty five bands observed in the IR spectra are assigned. The dehydration-induced deformations of the silicate rings are determined from the shifts of the vibrational bands of Si₆O₁₈. Institute of Mineralogy and Petrography, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 1, pp. 68–74, January–February, 1996. Translated by I. Izvekova     

Vibrational Spectroscopy and Analytical Electron Microscopy Studies of Fe–V–O and In–V–O Thin Films

Summary.  Orthovanadate (M ³⁺VO₄; M = Fe, In) and vanadate (Fe₂V₄O₁₃) thin films were prepared using sol-gel synthesis and dip coating deposition. Using analytical electron microscopy (AEM), the chemical composition and the degree of crystallization of the phases present in the thin Fe–V–O films were investigated. TEM samples were prepared in both orientations: parallel (plan view) and perpendicular (cross section) to the substrate. In the first stages of crystallization, when the particle sizes were in the nanometer range, the classical identification of phases using electron diffraction was not possible. Instead of measuring d values, experimentally selected area electron diffraction (SAED) patterns were compared to calculated (simulated) patterns in order to determine the phase composition. The problems of evaluating the ratio of amorphous and crystalline phases in thin films are reported. Results of TEM and XRD as well as IR and Raman spectroscopy showed that the films made at lower temperatures (300°C) consisted of nanograins embedded in the dominating amorphous phase. Characteristic vibrational spectra allowed to distinguish between the different crystalline phases, since the IR and Raman bands showed broadening due to the decreasing particle size of the films thermally treated at lower temperatures. Vibrational analysis also showed that the electrochemical cycling of crystalline films led to spectra that were in close agreement with the spectra of the nanocrystalline films prepared at lower temperatures. The formation of a nanocrystalline structure is therefore a prerequisite for obtaining a higher charging/discharging stability of Fe–V–O and In–V–O films. Received October 4, 2001. Accepted (revised) November 23, 2001     

Raman spectroscopic investigation of the antimalarial agent mefloquine

The antimalarial agent mefloquine was investigated using Fourier transform near-infrared (FT NIR) Raman and FT IR spectroscopy. The IR and Raman spectra were calculated with the help of density functional theory (DFT) and a very good agreement with the experimental spectra was achieved. These DFT calculations were applied to unambiguously assign the prominent features in the experimental vibrational spectra. The calculation of the potential energy distribution (PED) and the atomic displacements provide further valuable insight into the molecular vibrations. The most prominent NIR Raman bands at 1,363 cm⁻¹ and 1,434 cm⁻¹ are due to C=C stretching (in the quinoline part of mefloquine) and CH₂ wagging vibrations, while the most intense IR peaks at 1,314 cm⁻¹; 1,147 cm⁻¹; and 1,109 cm⁻¹ mainly consist of ring breathings and δCH (quinoline); C–F stretchings; and asymmetric ring breathings, C–O stretching as well as CH₂ twisting/rockings located at the piperidine moiety. Since the active agent (mefloquine) is usually present in very low concentrations within the biological samples, UV resonance Raman spectra of physiological solutions of mefloquine were recorded. By employing the detailed non-resonant mode assignment it was also possible to unambiguously identify the resonantly enhanced modes at 1,619 cm⁻¹, 1,603 cm⁻¹ and 1,586 cm⁻¹ in the UV Raman spectra as high symmetric C=C stretching vibrations in the quinoline part of mefloquine. These spectroscopic results are important for the interpretation of upcoming in vitro and in vivo mefloquine target interaction experiments.     

Synthesis, Crystal Structure, and IR Spectroscopic Characterization of 1,6-Hexanediammonium Dihydrogendecavanadate

Summary.  Anhydrous 1,6-hexanediammonium dihydrogendecavanadate ((HdaH₂)₂H₂V₁₀O₂₈, 1) was prepared by reaction of V₂O₅ with 1,6-hexanediamine in aqueous solution. The crystal structure of 1 was determined, and the proton positions in the H₂V₁₀O₂₈ ⁴⁻ anion were calculated by the bond length/bond number method. The protons are bound to the centrosymmetrically oriented μ–OV₃ groups of the decavanadate anion. Based on the analysis of IR spectra of 1 prepared from H₂O and D₂O, the absorption band at 871 cm⁻¹ can be attributed to δ(V–O_b–H) vibrations. Received August 3, 2001. Accepted (revised) October 8, 2001     

Spectroscopy of selected copper group minerals: ktenasite,orthoserpierite and kipushite

Near-infrared (NIR) and IR spectroscopy have been applied for the characterisation of three complex Cu–Zn sulphate/phosphate minerals, namely ktenasite, orthoserpierite and kipushite. The spectral signatures of the three minerals are quite distinct in relation to their composition and structure. The effect of structural cation substitution (Zn²⁺ and Cu²⁺) on band shifts is significant both in the electronic and in the vibrational spectra of these Cu–Zn minerals. The variable Cu:Zn ratio between Zn-rich and Cu-rich compositions shows a strong effect on Cu(II) bands in the electronic spectra. The Cu(II) spectrum is most significant in kipushite (Cu-rich) with bands displayed at high wavenumbers, 11,390 and 7,545 cm⁻¹. The isomorphic substitution of Cu²⁺ for Zn²⁺ is reflected in the NIR and IR spectroscopic signatures. The multiple bands for ν₃ and ν₄ (SO₄)²⁻ stretching vibrations in ktenasite and orthoserpierite are attributed to the reduction in symmetry of the sulphate ion from T_d to C_2V. The IR spectrum of kipushite is characterised by strong (PO₄)³⁻ vibrational modes at 1,090 and 990 cm⁻¹. The range of IR absorption is higher in ktenasite than in kipushite, while it is intermediate in orthoserpierite.     

Raman spectroscopic characterization of the microstructure of V2O5 films

The vanadium pentoxide (V₂O₅) films were deposited on silicon wafer by DC magnetron sputtering. By Raman scattering measurements, the microstructure properties of the V₂O₅ films prepared with different O₂–Ar gas flow ratios and annealed at different temperatures were studied, respectively. The results revealed that the increase of O₂–Ar gas flow ratio during sputtering was of advantage to prepare the V₂O₅ film with desired layer structure. A high post-annealing temperature (below 500 °C) induced the crystallization and the formation of the integrated structure of V₂O₅ film. However, it was found that both intensities of Raman scattering peaks at 146 cm^?1 and 994 cm^?1, respectively, decreased for samples annealed at a temperature of 550 °C. The peak at 146 cm^?1 was attributed to skeleton bent vibration and that at 994 cm^?1 was due to the stretching vibration of vanadyl V=O_A bond. It showed that the high-temperature annealing was believed to have distorted the microstructure of V₂O₅ films. The oxygen vacancies were, therefore, induced, which benefited the formation of V-O_A-V bonds between layers. The result of X-ray diffraction measurements was in good agreement with that of Raman scattering spectra.     

XPS study of nanorods of doped vanadium oxide MxV2O5 · nH2O (M = Na, K, Rb, Cs)

Nanorods of vanadium oxide doped with alkali metal ions M _x V₂O₅ · nH₂O (M = Na, K, Rb, Cs, x = 0.31–0.44) have been obtained under hydrothermal conditions. The particles are 30–80 nm in diameter and a few micrometers in length. The chemical state of atoms and their concentration ratios have been studied by XPS. It has been shown that vanadium atoms are in two oxidation states V⁵⁺ and V⁴⁺ and the concentration of vanadium(IV) ions directly depends on the alkali metal. The X-ray photoelectron spectra of the valence bands of M _x V₂O₅ · nH₂O (M = Na, K, Rb, Cs) nanorods have been measured and interpreted.     

CO and NO adsorption on VO x /SBA-15 catalysts: an FT-IR spectroscopic study

The adsorption of CO and NO over VO _x -SBA-15 mesoporous materials with different vanadium content was investigated by FT-IR spectroscopy. Vanadium complexes were reduced in situ by hydrogen atmosphere at 450 °C for 3 h. Spectra of reduced samples show increasing in intensity of silanol groups, caused by dissociation of V–O(Si) bonds and formation of new H–O(Si) bonds. Reduction occurs with formation of water. The band corresponds to overtone of V=O stretching modes decreases in intensity because of oxygen withdrawing from V=O species. Presence of V⁴⁺ and V³⁺ species was observed. Inspection of CO adsorbed IR spectra evidenced existence at least two different type of V³⁺–CO complexes on the silica surface differing in both stretching frequencies and complex stabilities. We did not found principal difference between spectra of absorbed CO at ?196 °C on the samples with different concentration of vanadium, probably because of relative low degree of reduction. As well as heterogeneity of surface V³⁺ and V⁴⁺ species was evidenced by adsorption of NO. Both V³⁺ and V⁴⁺ ions possess two effective coordinative vacancies and as a result can adsorb two NO molecules forming dinitrosyls. A part of V³⁺ cations forms only mononitrosyls characterize by band at 1724 cm^?1. Results obtained after NO adsorption reveal existence of three different kinds of vanadium species. Probably two of them are isolated and associated vanadium sites. The third type of vanadium has different surrounding than other two types. It was demonstrated that NO is a better probe than CO for testing the oxidation and coordination state of reduced vanadium species.     

Synthesis and characterization of dinuclear vanadium(V) oxido peroxido tartrato complexes

Vanadium(V) oxido peroxido tartrato complexes have been prepared from aqueous-ethanolic media and characterized by spectroscopic methods. Using racemic tartaric acid for the synthesis, the simultaneous crystallization of racemic compounds (racemic phases) and racemic conglomerates (chiral phases) has been observed. The X-ray crystal structure of (NH₄)₄[V₂O₂(O₂)₂((2R,3R)–H₂tart)₂(μ–H₂O)][V₂O₂(O₂)₂((2S,3S)–H₂tart)₂(μ–H₂O)]·8H₂O (tart = C₄H₂O₆ ⁴⁻) revealed that the dinuclear anion is composed of two pentagonal bipyramidal polyhedra about vanadium atoms, which are joined to each other by sharing two oxygen atoms of hydroxyl groups and an oxygen atom from a bridging water ligand. The prepared compounds are not stable in aqueous solution; ⁵¹V NMR spectra exhibit the signals of several peroxido and non-peroxido vanadium(V) complexes.     

V2O5/TiO2 Catalytic Xerogels Raman and EPR Studies

Raman spectroscopy and Electron Paramagnetic Resonance (EPR) studies were performed on a series of V₂O₅/TiO₂ catalysts prepared by a modified sol-gel method in order to identify the vanadium species. Two species of surface vanadium were identified by Raman measurements, monomeric vanadyls and polymeric vanadates. Monomeric vanadyls are characterized by a narrow Raman band at 1030 cm^–1 and polymeric vanadates by two broad bands in the region from 900 to 960 cm^–1 and 770 to 850 cm^–1. The Raman spectra do not exhibit characteristic peaks of crystalline V₂O₅. These results are in agreement with those of X-ray Diffractometry (XRD) and Fourier Transform Infrared (FT-IR) previously reported (C.B. Rodella et al., J. Sol-Gel Sci. Techn., submitted). At least three families of V⁴⁺ ions were identified by EPR investigations. The analysis of the EPR spectra suggests that isolated V⁴⁺ ions are located in sites with octahedral symmetry substituting for Ti⁴⁺ ions in the rutile structure. Magnetically interacting V⁴⁺ ions are also present as pairs or clusters giving rise to a broad and structureless EPR line. At higher concentration of V₂O₅, a partial oxidation of V⁴⁺ to V⁵⁺ is apparent from the EPR results.     

Ferroelectric properties of La and V co-substituted SrBi<Subscript>4</Subscript>Ti<Subscript>4</Subscript>O<Subscript>15</Subscript> films prepared by sol-gel method

SrBi₄Ti₄O₁₅ (SBTi), SrBi_3.89La_0.1Ti_3.97V_0.03O₁₅ (SBLTV) thin films have been fabricated on Pt/Ti/SiO₂/Si by the sol–gel method. Well-saturated hysteresis loops with remnant polarization around 46.7 μC/cm² are obtained on Pt/SBLTV/Pt capacitors. The capacitor shows excellent fatigue resistance with no polarization reduction up to 10⁹ switching cycles even at low test frequency of 50 kHz. The improvement of ferroelectric and fatigue-endurance properties are attributed to the La³⁺ and V⁵⁺ co-substitution, which brings about the concentration decrease and the mobility weakening of the defects.     

UV-Visible and IR Spectroelectrochemical Studies of FeVO4 Sol-Gel Films for Electrochromic Applications

The sol-gel synthesis route, in combination with dip-coating deposition, was used for the preparation of FeVO₄ films. TEM measurements of Fe/V (1 : 1)-oxide films heated at 400°C reveal that the films consist of a triclinic FeVO₄-I and an orthorhombic FeVO₄-II phases with a grain size of up to 50 nm. The electrochromic properties of the films were tested in 1 M LiClO₄/propylene carbonate (PC) using various electrochemical techniques and in-situ UV-visible spectroelectrochemical measurements. The best compromise between the charge capacity per film thickness (Qd^–1 = –0.14 mC cm^–2 nm^–1), electrochemical stability (>1000 cycles) and optical modulation (T_vis = 0.15) was achieved in the potential range of 4.80 to 1.80 V vs. Li, which suggests that FeVO₄ films can be used as counter-electrodes in electrochromic devices.Extensive IR-spectroscopy studies of FeVO₄ films in charged/discharged states revealed the following spectra changes: (i) small charging (–0.01 mC cm^–2 nm^–1) leads to a variation in the intensity of all the vibrational bands without shifting their frequencies, (ii) higher chargings bring about the intensity and frequency changes of bridging V—O···Fe and V···O···Fe stretchings showing that vanadium, and probably also iron, are involved in the insertion/extraction processes, (iii) below 500 cm^–1 broad absorption appears due to the Li⁺—O modes, which also remained in the IR spectra of discharged (bleached) states revealing the irreversible lithiation, and (iv) charging to –0.30 and –0.50 mC cm^–2 nm^–1 leads to the amorphisation of the film structure.     

Mechanochemical preparation of vanadium- and molybdenum-containing catalysts II: The effect of mechanochemical activation of vanadium pentoxide + ammonium dimolybdate compositions on chemical and phase transformations

We studied the effect of mechanochemical treatment (MCT) of V₂O₅ + (NH₄)₂Mo₂O₇ compositions (V: Mo = 0.7: 0.3) in ethanol, water, and air on the physicochemical properties of the compositions. X-ray powder diffraction, differential thermal analysis (DTA), and IR spectroscopy showed that mechanochemical treatment in water or ethanol does not change the phase state of vanadium pentoxide. (NH₄)₂Mo₂O₇ partially decomposes during MCT to yield nonstoichiometric molybdenum oxides. MCT in water leads to the complete decomposition of (NH₄)₂Mo₂O₇, and the nonstoichiometric molybdenum oxides that have been formed in 60–120 min are segregated into a molybdenum phase during further treatment for 240–360 min. During such a treatment, V₂O₅ first forms V₂O₅ · nH₂O intercalation compounds, which then react with ammonia during long-term treatment to form ammonium hexavanadate (AHV).     

Molecular structure of phthalocyaninato lanthanide LnPc(OAc) complexes derived from the FTIR and FT Raman studies

Room temperature Fourier transform IR and Raman spectra in the range 30–4000 cm⁻¹ and 80–4000 cm⁻¹ of Dy, Ho, Er and Lu phthalocyanide PcLn(OAc)-type complexes have been measured, respectively. The assignment of the bands observed has been made on the literature data. The molecular structure of the PcLnX-type derivatives has been discussed on the basis of the group theory taking into account the shape and number of the bands corresponding to the stretching and bending vibrations of the LnN₄O coordination polyhedron as well as whole PcLn(OAc) complex.     

Synthesis, V K β5β″ spectra, and magnetic properties of M4 ± x V6O16 ± x · n H2O (M = K, Rb, Cs) polyvanadates

Tetragonal polyvanadates M_{4 ± x} V₆O_{16 ± x} · nH₂O (M = K, Rb, Cs) have been synthesized under hydrothermal conditions. According to the VKβ₅β″ spectra of the hydrates, vanadium atoms have an average valence state (the V⁵⁺ ⇄ V⁴⁺ charge-fluctuation frequency is higher than 10⁻¹⁵ s). After dehydration, the phases do not change their crystal system. The thermal properties of the compounds have been studied in air and under an inert atmosphere. K_4.2V₆O_16.2 and Rb_4,1V₆O_16.1 melt congruently at 720 and 690°C, respectively. Cs_3.8V₆O_15.8 melts incongruently at 675°C. The magnetic susceptibility of all phases obeys the Curie-Weiss law in the range from 77 to 673 K. Original Russian Text ? V.L. Volkov, N.V. Podval’naya, V.M. Cherkashenko, S.N. Nemnonov, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 8, pp. 1272–1276.     

Modification and characterization of montmorillonite fillers used in composites with vulcanized natural rubber

Parent Ca-montmorillonite (Jelšovy Potok, Slovakia, Ca-JP) and Na-montmorillonite Kunipia-F (Japan, Na-KU) were ion-exchanged with octadecyltrimethylammonium (ODTMA) cations. Characteristics of the samples were studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (IR) and thermogravimetry (TG). Surface areas were measured by sorption of N₂ and ethyleneglycol monoethyl ether. Scanning electron microscopy photographs (SEM) were used to characterize the texture of samples. The XRD patterns show that, upon intercalation, the basal spacing of montmorillonite is expanded and corresponds to the pseudotrimolecular arrangement of organic cations in the interlayers. The IR spectra of organically modified montmorillonite show C-H stretching and bending bands of both CH₃ and CH₂ groups in the 3000–2800 cm⁻¹ and 1500–1400 cm⁻¹ region, respectively. Modification of montmorillonite by organic cations decreased the hydrophilicity of their mineral surface and adsorbed water evaporated at lower temperatures. The SEM photographs reveal a tendency towards lump formation and agglomeration of the ODTMA-montmorillonite particles. The modification introducing organic moiety lead to a substantial decrease in the surface area of both montmorillonites; however, it remained remarkably high, being at the level typical for silica. Completely characterized fillers were used to prepare rubber compositions with enhanced physical properties, as described in Hrachová et al. (2008).