Mössbauer Spectroscopic Study of xNa2O·5Fe2O3·(95-x)B2O3 Glasses (x=10–35)

A study of xNa₂O·5Fe₂O₃·(95-x)B₂O₃ glasses(x = 10–35) by Mössbauer spectroscopy was carried out in order to elucidate the effect of non-bridging oxygen (NBO) on Mössbauer parameters for Fe³⁺ ions. From the change of the isomer shift and quadrupole splitting, it was found that the Fe³⁺ ions in these borate glasses constitute FeO₄ tetrahedra and play a role of network former. These Mössbauer parameters reflect well the formation of NBO when N₂O contents is larger than 20 mol%. From the measurements of absorption area at low temperature, the _D values for Fe³⁺ ions in 10Na₂O·5Fe₂O₃·85B₂O₃ and 35Na₂O·5Fe₂O₃·60B₂O₃ glasses were determined to be 320 and 289 K, respectively. The decrease of _D value from 320 to 289 K is ascribed to the NBO which was formed by the breaking of -B-O-B- bonds.     

Phase formation in the system Zn(VO<Subscript>3</Subscript>)<Subscript>2</Subscript>–HCl–VOCl<Subscript>2</Subscript>–H<Subscript>2</Subscript>O

The phase and chemical compositions of precipitates formed in the system Zn(VO₃)₂–HCl–VOCl₂–H₂O at pH 1?3, molar ratio V⁴⁺: V⁵⁺ = 0.1?9, and 80°C were studied. It was shown that, within the range 0.4 ≤ V⁴⁺: V⁵⁺ ≤ 9, zinc vanadate with vanadium in a mixed oxidation state forms with the general formula Zn_xV⁴⁺ _yV⁵⁺ _2-yO₅ ? nH₂O (0.005 ≤ x ≤ 0.1, 0.05 ≤ y ≤ 0.3, n = 0.5?1.2). Vanadate Zn_xV₂O₅ ? nH₂O with the maximum tetravalent vanadium content (y = 0.30) was produced within the ratio range V⁴⁺: V⁵⁺ = 1.5?9.0. Investigation of the kinetics of the formation of Zn_xV₂O₅ ? nH₂O at pH 3 determined that tetravalent vanadium ions VO2+ activate the formation of zinc vanadate, and its precipitation is described by a second-order reaction. It was demonstrated that, under hydrothermal conditions at pH 3 and 180°C, zinc decavanadate in the presence of VOCl₂ can be used as a precursor for producing V₃O₇ ? H₂O nanorods 50–100 nm in diameter.     

Structural investigation and electron paramagnetic resonance of vanadyl doped alkali niobium borate glasses

Glasses with compositions xNb₂O₅·(30 ? x)M₂O·69B₂O₃ (where M = Li, Na, K; x = 0, 4, 8 mol%) doped with 1 mol% V₂O₅ have been prepared using normal melt quench technique. The IR transmission spectra of the glasses have been studied over the range 400–4000 cm^?1. The changes caused by the addition of Nb₂O₅ on the structure of these glasses have been reported. The electron paramagnetic resonance spectra of VO²⁺ ions in these glasses have been recorded in X-band (9.14 GHz) at room temperature (300 K). The spin Hamiltonian parameters, dipolar hyperfine coupling parameter and Fermi contact interaction parameter have been calculated. It is observed that the resultant resonance spectra contain hyperfine structures (hfs) due to V⁴⁺ ions which exist as VO²⁺ ions in octahedral coordination with a tetragonal compression in the present glasses. The tetragonality of V⁴⁺O₆ complex decreases with increasing concentration of Nb₂O₅. The 3d_xy orbit contracts with increase in Nb₂O₅:M₂O ratio. Values of the theoretical optical basicity, Λ_th, have also been reported.     

Electrochemical properties and state of paramagnetic centers in copper-modified complex vanadium and titanium oxides

Complex vanadium and titanium oxides modified by copper ions are studied by the electrochemical and ESR methods. Oxides Cu _x V_2?y Ti _y O_5?δ·nH₂O (0<y<1.33) have a layered structure and oxides Cu _x Ti_1?y V _y O_5+δ·nH₂O (0<y<0.25), an anatase structure. The intercalation of cations Cu²⁺ into the hydrates leads to oxidation of V⁴⁺. According to ESR data, V⁴⁺ exists in the oxides in the form of VO²⁺ and an octahedral surround of oxygen (V⁴⁺?O₆), respectively. The electroreduction of ions of d-elements and chemisorbed oxygen in the oxides is analyzed. The intercalation of cations Cu²⁺ alters the content of V⁴⁺ and the chemisorption ability of the oxides. Possible reasons for this phenomenon are discussed.     

Hydrolytic precipitation of magnesium polyvanadates in vanadium (IV, V) solutions

The phase and chemical composition of precipitates formed in Mg(VO₃)₂-VOSO4-H₂O system at initial pH from 1 to 7 and temperature from 80 to 90°C was studied. Polyvanadates of variable composition Mg _x V _y ⁴⁺V_12-y ⁵⁺¹O_31–δ · nH₂O (0.7 ≤ x ≤ 1.3, 1.2 ≤ y ≤ 2.4, 0.7 ≤ δ = 1.4) were formed at pH from 1 to 4 and V⁴⁺/V⁵⁺ ratio from 0.43 to 9. Compounds with the general formula Mg _x V _y ⁴⁺V_6-y ⁵⁺O_16-δ · nH₂O (0.7 ≤ x ≤ 0.65, y = 1.0, 0.8 ≤ δ ≤ 0.85) were formed at pH from 6.0 to 7.0 and V⁴⁺/V⁵⁺ ratios from 0.11 to 0.25. The maximum V⁴⁺ concentration (y = 2.4) in the precipitates was achieved at the VV⁴⁺/V⁵⁺ solution ratio of 1.0 and pH = 3. The precipitates in solutions with pH 3 were formed only upon addition of VO²⁺ ions with the maximum rate at a V⁴⁺/V⁵⁺ ratio of 0.33. These processes were limited by second-order reactions on the surface of polyvanadates.     

Mössbauer and electrical investigation of sulfur-doped sodium borate glasses containing iron

Three series of sulfur-doped sodium tetraborate glasses containingiron was prepared with the composition (Na₂ B₄ O₇ ) _1–x (Fe₂ O ₃ ) x , wherex equals 0.1, 0.2 and 0.3. One series of the glass was left free of sulfur,while sulfur was added to the other two series of 2.5 and 5 wt%, respectively,to investigate the role of sulfur ions on some physical properties of thistype of glass. Melting process was carried out in platinum crucibles at 1100°C for one hour. The glasses were quenched in air at room temperature.X-ray diffraction measurement was carried out to be sure that the pure glassystate is obtained. ⁵⁷Fe Mössbauer spectroscopy and dc conductivitymeasurements were carried out. It was found that iron is present in form ofFe²⁺ and Fe ³⁺ ions. Sulfur ions increased the valuesof dc conductivity. The isomer shift of the two states of iron is stable whilethe quadrupole splitting value changed with increasing Fe₂ O₃ content or as sulfur was added.     

57Fe- and119Sn-Mössbauer effect of oxide glasses

Coordination number of network-former (NWF) and formation of nonbridging oxygen (NBO) at the site neighboring to NWF can be estimated from Mössbauer measurements, since small amounts of Fe³⁺ and Sn⁴⁺ substitute NWF in several oxide glasses. Gamma-ray or thermal neutron irradiation of oxide glasses causes electron or charge transfer from oxygen to the Mössbauer ions, and the probability depends on the fraction of NBO. On the contrary, -ray irradiation of phosphate glasses results in oxidation of Fe²⁺ to Fe³⁺ since iron plays a role of network modifier (NWM) at interstitial sites. Debye temperature _D obtained from low-temperature Mössbauer measurements reflects the site occupation of Mössbauer ions in glasses. A linear relationship between glass transition temperature (T _g ) and quadrupole splitting () of Fe³⁺,T _g — rule, is also effective for determining the site occupation of Mössbauer ions.     

Weitere magnetische Untersuchungen an Ti3−xMxO5-Phasen (M = Al3+, Fe2+, Mn2+, Mg2+) mit einem Beitrag über CrTi2O5

Additional Magnetic Examinations of Ti_3?xM_xO₅-Phases (M = Al³⁺, Fe²⁺, Mn²⁺, Mg²⁺) with a Contribution about CrTi₂O₅ Ti_3?xM_xO₅ was prepared with M = Al³⁺, Fe²⁺, Mn²⁺, and Mg²⁺. Die magnetic properties of this phases were examinated by the Faraday method in respect to the temperature. The well known magnetic effect of Ti₃O₅ near 450 K is shifted to lower degrees if Ti is replaced by Al, Fe, Mn, or Mg. Compared to Ti_3?xV_xO₅ and Ti_3?xCr_xO₅ the stability of the low temperature-form of Ti₃O₅ is much more reduced in Ti_3?xM_xO₅ (M = Al, Fe, Mn, Mg). The crystal structure investigation of CrTi₂O₅ explained the anomalous behaviour of the Cr³⁺ and V³⁺ doped Ti₃O₅.     

Mechanisms of molybdenum substitution in vanadium antimonate

The formation of a solid solution containing the three elements V, Sb and Mo, which are key-elements in the design of light alkane oxidation catalysts, has been studied by incorporating molybdenum into the pure VSbO₄ compound as obtained in air at 700°C (V³⁺_0.28V⁴⁺_0.64□_0.16Sb⁵⁺_0.92O₄). Monophasic compounds with a rutile-type structure have been obtained and characterized by X-ray diffraction, electron microscopy, Infrared Fourier transform, X-ray absorption and electron spin resonance spectroscopies. At low molybdenum content, Mo⁶⁺ substitute V⁴⁺ in the cationic-deficient structure. The charge balance is maintained by an increase of the cationic vacancy number. This leads to the formation of a solid solution corresponding to the formula V³⁺_0.28V⁴⁺_0.64−3xMo⁶⁺_2x□_0.16+xSb⁵⁺_0.92O₄ with 0<x<0.09. At higher molybdenum content, Mo⁵⁺ are stabilized and substitute Sb⁵⁺ in the rutile structure: V³⁺_0.28V⁴⁺_0.37Mo⁶⁺_0.18□_0.25Mo⁵⁺_ySb⁵⁺_0.9−yO₄ with 0<y<0.06. At higher molybdenum content the rutile phase is no longer stable and two new phases are formed: Sb₂O₄ and a new mixed vanadium molybdenum antimonate.     

Composition and formation kinetics of strontium polyvanadates in vanadium(IV,V) solutions

The phase and chemical compositions of the precipitates forming in the Sr(VO₃)₂-VOCl₂-H₂O system in the V⁴⁺/V⁵⁺ = 0.11–9 range at 80–90°C are reported. At pH 1–3 and V⁴⁺/V⁵⁺ = 0.25−9, the general formula of the precipitated compounds is Sr _x V _y ⁴⁺ V_12−y ⁵⁺O_31−δ·nH₂)(0.37 ≤ x ≤ 1.0, 1.7 ≤ y ≤ 3.0, 0.95 ≤ δ ≤ 2.1). Polyvanadates containing the largest amount of vanadium(IV) are obtained at an initial V⁴⁺/V⁵⁺ ratio of 9 and pH 1.9. Precipitation from solutions at pH 3 takes place only in the presence of the VO²⁺ ion, and the highest precipitation rate is observed at V⁴⁺/V⁵⁺ = 0.11. The process is controlled by a second-order reaction on the polyvanadate surface. Under hydrothermal conditions at 180°C, Sr_0.25V₂O₅·1.5H₂O nanorods are obtained from solutions with a V⁴⁺/V⁵⁺ molar ratio of 0.1 at pH 3. The nanorods, 30–100 nm in diameter and up to 2–3 μm in length, have a layered structure with an interlayer spacing of 10.53 ± 0.08 ?.     

Hydrolytic precipitation of calcium polyvanadates from vanadium(IV) and vanadium(V) solutions

The effect of VO²⁺ ions on the composition and kinetics of calcium polyvanadate precipitation from solutions with 1.5 ≤ pH ≤ 9 at 80–90°C has been studied. For 1,5 ≤ pH < 3 and V⁴⁺/V⁵⁺ = 0.11–9, the precipitated compounds have the general formula Ca _x V _y ⁴⁺ V _12?y ⁵⁺ O_31?δ · nH₂O (0.8 ≤ x ≤ 1.06, 2 ≤ y ≤ 3, 0.94 ≤ δ ≤ 1.5). The maximum vanadium(IV) proportion (y = 3) in the precipitates is achieved when V⁴⁺/V⁵⁺ = 0.5?1.0 in the solution and pH is 3. Polyvanadate precipitation at pH 1.7 has a long induction period (up to 30 min), which is not observed for V⁴⁺/V⁵⁺ > 0.1. Precipitation in solutions with pH 3 occurs only when VO²⁺ ions are added, with a maximum rate near V⁴⁺/V⁵⁺ = 0.2 and in presence of chloride ions. The processes are controlled by a secondorder reaction on the polyvanadate surface.     

Magnetische Eigenschaften von Ti3−xMxO5-Phasen (M = V3+, Cr3+, Nb4+)

Magnetic Properties of Ti_3?xM_xO₅ Phases (M = V³⁺, Cr³⁺, Nb⁴⁺) The magnetic properties of Ti_3?xV_xO₅, Ti_3?xCr_xO₅, and Ti_3?xNb_xO₅ phases are reported. In the case of V³⁺ and Cr³⁺ the magnetic leaping-temperature decreases, however Nb⁴⁺ shift the phase-transition towards higher temperatures. All samples show a “memory-effect” in magnetic properties, i. e. the results of heating- and cooling-cycles are higher susceptibilities of the α-phase of Ti₃O₅. Endowed Ti₃O₅ phases show for the α- and β-Ti_3?xM_xO₅ til the leap Curie-Weiss characteristic in 1/X vs. temperature measurements. Exception is β-Ti_3?xNb_xO₅, its susceptibility is independend of the temperature up to x ? 0.3.     

Thermal behaviour and fragility of Sb<Subscript>2</Subscript>O<Subscript>3</Subscript>-containing zinc borophosphate glasses

Thermal behaviour of the glass series (100-x)[50ZnO-10B₂O₃-40P₂O₅]·xSb₂O₃ (x=0-42 mol%) and (100-y)[60ZnO-10B₂O₃-30P₂O₅]·ySb₂O₃ (y=0-28 mol%) was investigated by DSC and TMA. The addition of Sb₂O₃ results in a decrease of the glass transition temperature and crystallization temperature in both compositional series. All glasses crystallize on heating in the temperature range of 522–632°C. Thermal expansion coefficient of the glasses monotonously increases with increasing Sb₂O₃ content in both series and varies within the range of 6.6–11.7 ppm °C⁻¹. From changes of thermal capacity within the glass transition region it was concluded that with increasing Sb₂O₃ content the ‘fragility’ of the studied glasses increases.     

Thermal,IR, Raman characteristics,Raman gain coefficient and bandwidths in quaternary glasses

Tellurite glasses with composition 75TeO₂–5WO₃–15Nb₂O₅–5M_xO_y in mol%, where M_xO_y = (Na₂O, Ag₂O, ZnO, MgO, CuO, NiO, TiO₂, MnO₂) have been prepared by using the conventional melt-quenching method. Thermal characteristic of prepared glasses were investigated by using DTA techniques. It was found that the glass with the composition 751TeO₂–5WO₃–15Nb₂O₅–5TiO₂ had high thermal stability (ΔT = 122 °C at heating rate 15 K/min). Raman gain coefficients and bandwidths of prepared glasses for Raman gain media were evaluated. The glass with composition 75TeO₂–5WO₃–15Nb₂O₅–5Na₂O had the maximum value of Raman gain coefficient (g = 4.43 × 10⁻¹² m/W) and it was 24 times as large as silica glass. The highest value of full width half maximum (FWHM ≈ 185 cm⁻¹) was observed in glass system 75TeO₂–5WO₃–15Nb₂O₅–5NiO. Finally, the structure of the glasses was investigated through deconvolution Raman and IR spectra.     

Composition and formation kinetics of sodium polyvanadates in vanadium(IV, V) solutions

We study how VO²⁺ ions affect the composition and formation kinetics of polyvanadate precipitates in solutions with 1 ≤ pH ≤ 3 at 80–90°C. The compounds have the general formula Na_2.1?x H_xV _y ⁴⁺ V _12?y ⁵⁺ O_31?δ. nH₂O (0 ≤ x ≤ 1.1, 0.2 ≤ y ≤ 2.3, 0.1 ≤ δ ≤ 1.4). The maximal vanadium(IV) concentration in the precipitates y = 2.2 and 2.3) is achieved for the V⁴⁺/V⁵⁺ ratio in the solution equal to 0.5 and 0.3 and pH of 1.7 and 3.0, respectively. The polyvanadate precipitation at pH 1.7 has a long induction period, which is not observed when V⁴⁺/V⁵⁺ > 0.02. In the solutions with pH 3.0, the precipitation occurs only when VO²⁺ are added. The processes are controlled by second-order reactions on the polyvanadate surface.     

EPR investigation and thermal study of yA<Subscript>2</Subscript>O-(1-<Emphasis Type="Italic">y</Emphasis>)[0.25(WO<Subscript>3</Subscript>)<Subscript>2</Subscript>-0.75(P<Subscript>2</Subscript>O<Subscript>5</Subscript>)] (A=Li,Na) glasses

Summary Glasses belonging to the series yA₂O-(1-y)[0.25(WO₃)_2-0.75P₂O₅] (y=0.10-0.60) are elaborated. DTA experiments reveal that the glass-network of the glasses are broken with increasing of modifier content. EPR spectra show the presence of two signals due to W⁵⁺ and Mo⁵⁺, as impuritie. The intensity of these EPR centres decreases when the concentration of A₂O increases. The variation of T_g upon the modifier content is ascribed to structural changes occurring in the matrix of these glasses.     

Approach to thermal properties and electronic polarizability from average single bond strength in ZnOBi2O3B2O3 glasses

The glass transition temperature (T_g), density, refractive index, Raman scattering spectra, and X-ray photoelectron spectra (XPS) for xZnO-yBi₂O₃-zB₂O₃ glasses (x=10-65, y=10-50, z=25-60 mol%) are measured to clarify the bonding and structure features of the glasses with large amounts of ZnO. The average electronic polarizability of oxide ions (α_O2−) and optical basicity (Λ) of the glasses estimated using Lorentz-Lorenz equation increase with increasing ZnO or Bi₂O₃ content, giving the values of α_O2−=1.963 Å³ and Λ=0.819 for 60ZnO-10Bi₂O₃-30B₂O₃ glass. The formation of BOBi and BOZn bridging bonds in the glass structure is suggested from Raman and XPS spectra. The average single bond strength (B_MO) proposed by Dimitrov and Komatsu is applied to the glasses and is calculated using single bond strengths of 150.6 kJ/mol for ZnO bonds in ZnO₄ groups, 102.5 kJ/mol for BiO bonds in BiO₆ groups, 498 kJ/mol for BO bonds in BO₃ groups, and 373 kJ/mol for BO bonds in BO₄ groups. Good correlations are observed between T_g and B_MO, Λ and B_MO, and T_g and Λ, proposing that the average single bond strength is a good parameter for understanding thermal and optical properties of ZnOBi₂O₃B₂O₃ glasses.     

Color Point Tuning in Lu3−x−yMnxAl5−xSixO12:yCe3+ for White LEDs

A series of the solid‐solution phosphors Lu_3?x?yMn_xAl_5?xSi_xO₁₂:yCe³⁺ is synthesized by solid‐state reaction. The obtained phosphors possess the garnet structure and exhibit similar excitation properties as the phosphor Lu₃Al₅O₁₂:Ce³⁺, but with an effectively improved red component in the emission spectrum. This can be attributed to the energy transfer from Ce³⁺ to Mn²⁺. Our investigation reveals that electric dipole–quadrupole interactions dominate the energy‐transfer mechanism and that the critical distance determined by the spectral overlap method is about 9.21 Å. The color‐tunable emissions of the Lu_3?x?yMn_xAl_5?xSi_xO₁₂:yCe³⁺ phosphor as a function of Mn₃Al₂Si₃O₁₂ content are realized by continuously shifting the chromaticity coordinates from (0.354, 0.570) to (0.462, 0.494). They indicate that the obtained material may have potential application as a blue radiation‐converting phosphor for white LEDs with high‐quality white light.     

Theoretical studies of the concentration dependences of d–d transition band,g factors,and local distortion for V4+ in Li2O–PbO–B2O3–P2O5 glasses

In this work, the g factors, d–d transition band, local distortion, and their concentration dependences for impurity V⁴⁺ in 20Li₂O–20PbO–45B₂O₃–(15 − x)P₂O₅:V₂O₅ (0 ≤ x ≤ 2.5 mol%) glasses are theoretically investigated by using perturbation formulas of g factors for a tetragonally compressed octahedral 3d¹ cluster. In the light of the cubic polynomial concentration functions for cubic field parameter D_q, covalency factor N, and relative tetragonal compression ratio ρ, the calculated concentration dependences of d–d transition band and g factors for V⁴⁺ show good agreement with the experimental data. With increasing x, N (≈0.7682–0.8165) displays the monotonously increasing trend, whereas ρ (≈6.5–4.2%) and D_q (≈1504.9–1481.1 cm⁻¹) exhibit the decreasing tendencies. The above concentration dependences can be ascribed to the modifications of the V⁴⁺–O²⁻ bonding and orbital admixtures around the impurity V⁴⁺ due to the effects of V₂O₅ doping on the stability of the glass network, the strength of local crystal fields, and the electron cloud distribution.     

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.