57Fe-Mössbauer study of electrically conducting barium iron vanadate glass after heat treatment

Local structure and thermal durability of semiconducting xBaO·(90?? x)V₂O₅ · 10Fe₂O₃ glasses (x = 20, 30 and 40), NTA glass ^TM, before and after isothermal annealing were investigated by ⁵⁷Fe-Mössbauer spectroscopy and differential thermal analysis (DTA). An identical isomer shift ( $\mathit{\delta}$ ) of 0.39 ± 0.01 mm s^???1 and a systematic increase in the quadrupole splitting (Δ) were observed from 0.70 ± 0.02 to 0.80 ± 0.02 mm s^???1 with an increasing BaO content, showing an increase in the local distortion of Fe^IIIO₄ tetrahedra. From the slope of the straight line in the T _g–Δ plot of NTA glass ^TM, it proved that Fe^III plays a role of network former. Large Debye temperature (Θ _D) values of 1000 and 486 K were respectively obtained for 20BaO · 70V₂O₅ · 10Fe₂O₃ glass before and after isothermal annealing at 400°C for 60 min, respectively. This result also suggests that Fe^III atoms constitute the glass network composed of tetrahedral FeO₄, tetrahedral VO₄ and pyramidal VO₅ units. The electric conductivity of 20BaO · 70V₂O₅ · 10Fe₂O₃ glass increased from 1.6 × 10^???5 to 5.8 × 10^???2 S cm^???1 after isothermal annealing at 450°C for 2,000 min. These results suggest that the drastic increase in the electric conductivity caused by heat treatment is closely related to the structural relaxation of the glass network structure.     

Electrical conductivity and local structure of lithium tin iron vanadate glass

A relationship between electrical conductivity (σ) and local structure of 15Li₂O·10Fe₂O₃·xSnO₂·(70–x)V₂O₅·5P₂O₅ glass (x = 0–20 mol%), abbreviated as xLFSVP glass, was investigated by ⁵⁷Fe- and ¹¹⁹Sn-Mössbauer spectroscopies, differential thermal analysis (DTA) and dc-four probe method. A small increase in quadrupole splitting (Δ) for Fe^III was observed from 0.70 to 0.74_{± 0.02} mm s^???1 with an increase of “x”, whereas isomer shift (Δ) values of 0.40_±0.01 mm s^???1 were independent of “x”. This result suggests that local distortion of Fe^IIIO₄ tetrahedra was slightly increased in SnO₂-containing vanadate glasses, which was reflected as an increase in glass transition temperature (T_g) from 266 to 285_±5 °C. A slope of 675 K / (mm s^???1) obtained in ‘T_g vs. Δ plot’ proved that Fe^III occupied the site of network former (NWF). An isothermal annealing of 10LFSVP glass at 500 °C for 100 min resulted in a marked decrease of Δ from 0.72 to 0.56_±0.02 mm s^???1, indicating that local distortion of FeO₄ tetrahedra was reduced by the structural relaxation of 3D-network. In contrast, identical δ and Δ values of 0.07_±0.01 and 0.53_±0.02 mms^???1, respectively, were observed in ¹¹⁹Sn-Mössbauer spectra of 10LFSVP glass before and after the annealing. These results indicate that Sn^IVO₆ octahedra are loosely bound in the glass matrix as a network modifier (NWM). A marked increase in σ from 7.4 × 10^???7 to 9.1 × 10^???3 S cm^???1 was observed in 20LFSVP glass after the isothermal annealing, indicating that structural relaxation of 3D-network evidently causes a marked increase in σ.     

IR and Raman investigation on the structure of (100-x)B2O3-x[0.5 BaO-0.5 ZnO] glasses

Glasses with molar composition of (100-x)B₂O₃-x[0.5 BaO-0.5 ZnO], x=40, 50, 60, 70 were prepared from the melts of ZnO, BaCO₃ and H₃BO₃ mixture. The structure and thermal behavior were characterized by IR and Raman spectroscopy, DSC and Dilatometer. The investigation shows that the transition of the structural unit [BO₄] (B^IV) to [BO₃] (B^III) happens when BaO and ZnO content x increases in the borate glass, resulting in fewer B^III-O-B^IV bonds and more B^III-O-B^III bonds. At the same time, the diborate groups, which are found to be the predominant structural group of the glass with high B₂O₃ content, gradually changes into ring-type metaborate, pyro- and orthoborate groups. With increasing ZnO and BaO content x, the glass transition temperature (T_g) and the softening point (T_f) decreases, while linear expansion coefficient (α) increases, that comes from the weakening of the glass network.     

Volume and surface oxidation of basalt

Natural, Fe²⁺-rich basalt glass (quenched lava) was heat treated as glass pieces and glass powder in air, in 6.0 Ar and in a 9×10^?6 mbar vacuum below temperatures of significant crystallization to access volume and surface oxidation by ⁵⁷Fe Mössbauer spectroscopy. While no oxidation occurs upon heating in vacuum, the amount of Fe³⁺ formed in powder (surface oxidation) is about 10 times higher than in pieces (volume oxidation), and surface oxidation is of the same order in air and Ar. This effect is assigned to chemisorption of water or CO₂. Crystalline basalt, investigated by wet chemistry, includes five glass pieces treated above T of crystallization in air and in 6.0 Ar, and three lava samples of increasing depth up to 9 cm of lava lobes. The high Fe₂O₃ of all these crystalline samples is explained as a stabilization of Fe³⁺ due to the change of the local electronic environment in the course of crystallization; volume oxidation therefore appears to be independent on the environmental atmosphere.     

Core and valence level photoemission studies of iron oxide surfaces and the oxidation of iron

The core and valence level XPS spectra of Fe_xO (x ~ 0.90–0.95); Fe₂O₃ (α and γ); Fe₃O₄; and FeOOH have been studied under a variety of sample surface conditions. The oxides may be characterized by a combination of valence level differences and core-level effects (chemical shifts, multiplet splittings, and shake-up structure). Fe^II and Fe^III states are distinguishable, but octahedral and tetrahedral sites are not. The O 1 s BE cannot be used to distinghuish between the oxides since it has a nearly constant value. Fe 3d valence level structure spreads some 10 eV below E_F, much broader than suggested by previous UPS and photoelectron-spin-polarization (ESP) measurements for Fe_xO and Fe₃O₄. Fe surfaces (films, foils, (100) face) yield predominantly Fe^III species when exposed to high exposures of oxygen or air, though there is evidence for some Fe^II also. At low exposures the Fe^II/Fe^III ratio increases.     

Mossbauer, infrared and magnetic susceptibility studies of iron sodium borate glasses doped by sulphur

The affect of sulphur on the structural properties of iron sodium diborate glasses having the composition {(100−x)Na₂B₄O₇+xFe₂O₃}+yS, where x=0.05, 0.15 and 0.25 mol% and Y=0, 2.5 and 5 wt% was studied by infrared, Mossbauer spectroscopy and magnetic susceptibility measurements. It was found that, for samples having 5 mol% Fe₂O₃ and free from sulphur, the iron ions are present in both Fe²⁺ and Fe³⁺ states and also 92% of the total iron enters the glass network as a glass former. The ratio of Fe³⁺/Fe²⁺ increases with increasing the iron content for sulphur-free samples and others containing sulphur. This ratio also decreases with increasing the sulphur content. The magnetic susceptibility was found to decrease with increasing the sulphur content. Also, the increase of Fe₂O₃ content led to a less symmetrical environment of Fe³⁺ ions and vice versa for the Fe²⁺ environment.     

Water cleaning ability and local structure of iron-containing soda-lime silicate glass

A relationship between waste-water cleaning ability and local structure of iron-containing soda-lime silicate glass, 15Na₂O·15CaO·xFe₂O₃·(70-x)SiO₂ (x?= 10–50 in mass%), abbreviated as NCFSx glass, was investigated by means of ⁵⁷Fe-Mössbauer spectroscopy, redox titration with KMnO₄ for the determination of chemical oxygen demand (COD) and inductively coupled plasma optical emission spectroscopy (ICP-OES). Mössbauer spectra of NCFSx glass with “x” of 10 and 30 were composed of two doublets: one due to Fe^IIIO₄ tetrahedra (T _d) with isomer shift (δ) of 0.23–0.26 mm s^???1 and quadrupole splitting (Δ) 1.01–1.04 mm s^???1, and the other due to Fe^IIO₆ octahedra (O _h) with δ of 1.00–1.03 mm s^???1 and Δ of 2.03–2.05 mm s^???1. Absorption area for Fe^II(T _d) was decreased from 9.7 to 6.5 and 0.0 % when “x” was increased from 10 to 30 and 50. A leaching test performed with 500 mL of artificial waste water and 2.0 g of NCFS50 revealed waste-water cleaning ability of soda-lime glass, e.g., COD was reduced from 280 to 55.2 mg L^???1 after 10 day-leaching. After 10 day-leaching, it proved that iron was dissolved into waste water to a level of 5.3 $_{7} \times 10^{-1}$  mg L^???1. These results prove that organic matter could be effectively decomposed with iron-containing soda-lime silicate glass.     

Stabilization of the anatase phase in TiO2(Fe, PEG) nanostructured coatings

Multilayered TiO₂(Fe³⁺, PEG) films were deposited on glass and SiO₂/glass substrates by sol-gel dipping method. The influence of Fe³⁺ and PEG(polyethylene glycol) concentrations, the number of layers, the thermal treatment time and the temperature on the optical and microstructural properties of the TiO₂ films were studied.As-deposited TiO₂(Fe³⁺, PEG) films were very porous, but after the thermal treatment at 500 °C, the PEG decomposed and burned out to porosity decreasing. Homogeneous nanostructured films were obtained, where the amorphous and the anatase phases coexist. XRD analysis showed that no rutile phase is observed in the films deposited on SiO₂/glass as compared with those deposited directly on glass and that the presence of the anatase phase in the films without PEG is more evident in the three-layers film. The XRD intensity of the main peak of anatase from 25° decreases with the increase of PEG concentration.The optical gap of the TiO₂(Fe³⁺, PEG) films is found in 2.52-2.56 eV range and does not essentially depend on the PEG content.     

Luminescence studies on ZnO-P2O5 glasses doped with Gd2O3:Eu nanoparticles and Eu2O3

Zinc phosphate glasses doped with Gd₂O₃:Eu nanoparticles and Eu₂O₃ were prepared by conventional melt-quench method and characterized for their luminescence properties. Binary ZnO-P₂O₅ glass is characterized by an intrinsic defect centre emission around 324 nm. Strong energy transfer from these defect centres to Eu³⁺ ions has been observed when Eu₂O₃ is incorporated in ZnO-P₂O₅ glasses. Lack of energy transfer from these defect centres to Eu³⁺ in Gd₂O₃:Eu nanoparticles doped ZnO-P₂O₅ glass has been attributed to effective shielding of Eu³⁺ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between the luminescent centre and Eu³⁺ ions. Both doped and undoped glasses have the same glass transition temperature, suggesting that the phosphate network is not significantly affected by the Gd₂O₃:Eu nanoparticles or Eu₂O₃ incorporation.     

Mössbauer study of amorphous BaO−Fe2O3−B2O3 system

HomogeneousBaO?Fe₂O₃?B₂O₃ glasses containing maximum Fe₂O₃ content of 63 mol.% are prepared by splat cooling technique. Mössbauer study reveals that the glass mainly consists of tetrahedral network of Fe³⁺O₄. Mössbauer spectrum of the glass shows a well defined hyperfine structure at low temperatures. Magnetic ordering temperature estimated is about 130 K for the most iron-rich specimen, being much lower than that of the corresponding crystalline phases, BaO;·;Fe₂O₃ and BaO·;2Fe₂O₃. The magnetic structure is suggested to be of a short-range antiferromagnetic ordering.     

Effect of high magnetic field annealing on the microstructure and magnetic properties of Co-Fe layered double hydroxide

The effects of high magnetic field (10 T) on the products obtained by calcination of Co-Fe LDH precursors at different temperatures were investigated. The XRD results indicated that Fe^III substituted for Co^III in Co₃O₄ to yield Co^IICo^IIIFe^IIIO₄ under the calcination of Co-Fe LDH precursors at 400 °C. The products obtained by magnetic field annealing at 400 °C had a porous plate-like morphology, whereas the products without magnetic field annealing were composed of nanoparticles. It was seen that CoFe₂O₄ phase could be formed at low temperature (about 500 °C) under the magnetic field annealing. The grain size of products obtained by magnetic field annealing at 800 °C was larger than that of zero magnetic field. It was found that the saturation magnetization was significantly enhanced after magnetic field annealing, especially at lower temperature (≤600 °C). The possible reason for the effects on the microstructure and magnetic properties of products obtained by magnetic field annealing was discussed.     

Optical spectroscopic analysis of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> doped CuO containing phosphate glass

The effect of Fe₂O₃ in sodium zinc phosphate glass system containing CuO with the chemical composition 40P₂O₅:38ZnO:1CuO:(21 ? x)Na₂O:xFe₂O₃ (where x = 1, 2, 3, 4, 5 and 6 mol%) has been studied. The glass formability of the prepared samples was examined by means of XRD which proved that there are no natural crystal contents. Archimedes method has been employed to measure the density of the prepared glass samples hence, the molar volume was calculated. The density and the molar volume were found to be increased by increasing Fe₂O₃ content. The optical spectroscopic analysis for the obtained glass samples has been carried out over the whole range (190–1000 nm) for studying the effect of bandpass absorption glass filter, its color peak center and UV cut-off. The center for bandpass filter is found to exhibit a red shift by increasing Fe₂O₃ content. Moreover, all glass samples showed a bandstop in UV-range which was increased by increasing Fe₂O₃ content. The results reveal the practicality of this glass composition in optical color glass bandpass filter for UV preventing applications such as UV-Laser protection.     

Effect of iron doping on the characterization and transport properties of calcium phosphate glassy semiconductors

X-ray diffraction (XRD), differential scanning calorimeter (DSC), density (d) and dc conductivity (σ) of the glasses in Fe₂O₃-CaO-P₂O₅ system were reported. The dc conductivity in the temperature range 303-453 K was measured. The overall features of these XRD curves confirm the amorphous nature of the present samples. The density of glasses increases from 2.750 to 2.892 g/cm³ with increasing Fe₂O₃ content as a result of a strengthening of cross-linking within glass network. The glass temperature values (T_g) of the present glasses were larger than those of tellurite glasses. This indicates a higher thermal stability of the glass in the present system. The glasses had conductivities ranging from 10⁻⁹ to 10⁻⁵ Sm⁻¹ at temperatures from 303 to 453 K. Electrical conduction of the glasses was confirmed to be due to non-adiabatic small polaron hopping and the conduction was primarily determined by hopping carrier mobility.     

Magnetism in some layer molecular magnets as revealed by Mössbauer spectroscopy

⁵⁷Fe Mössbauer spectroscopy was used to explore magnetic properties of two 2D molecular ferrimagnets. In NPn₄[Fe^IIFe^III(ox)₃] (Pn = n-C₅H₁₁, (ox) =(C₂O₄)^2?), the previously reported negative magnetization is shown here by external field studies to be due to a cross-over between Fe^III and Fe^II- magnetizations. The form and parameters of the magnetic Hamiltonian describing the temperature dependence of both the Fe^III hf-field and net magnetizations has been determined. In NBu₄[Mn^IIFe^III(ox)₃] (Bu = n-C₄H₉) soft XY-magnet the low temperature relaxation spectra are interpreted in terms of slowly varying classical magnetization-evolution at low temperature.     

Mössbauer studies of phosphate glasses for the immobilisation of toxic and nuclear wastes

Various iron-containing phosphate glasses were investigated by Mössbauer spectroscopy. Iron was found to occur predominantly as Fe³⁺ in all glasses, and largely occupied sites with distorted octahedral coordination for both redox states. Using a base glass of nominal composition 60 P₂O₅–40 Fe₂O₃ (mol%), stepwise molar replacement of Fe₂O₃ by (0.67 Na₂O?×?0.33 Al₂O₃) increased the redox ratio, Fe²⁺/ΣFe, from 0.13 at 40% Fe₂O₃ to 0.25 at 10% Fe₂O₃. The centre shift increased and quadrupole splitting decreased by up to ～20% over this range, interpreted as a decrease in the average distortion of Fe sites from cubic symmetry, and an increase in average iron coordination. Literature revealed that recoil-free fraction ratio f (Fe³⁺)?/?f (Fe²⁺)?≈?1.3 in iron phosphate glasses, and this was considered when assessing redox. Mössbauer parameters of these and other glasses demonstrated a combination of structural stability and compositional flexibility which makes them so suitable for waste immobilisation.     

Local structure and water cleaning ability of iron oxide nanoparticles prepared by hydro-thermal reaction

Nanoparticles (NPs) of Fe₃O₄ and γFe₂O₃ synthesized by hydrothermal reaction were characterized by X-ray diffractometry (XRD), ⁵⁷Fe-Mössbauer spectroscopy and field emission scanning electron microscopy (FE-SEM). A decrease in concentration of methylene blue (MB) aqueous solution due to bulk Fe⁰-NP γFe₂O₃ mixture with the mass ratio of 3:7 was measured by ultraviolet-visible light absorption spectroscopy (UV-Vis). The Mössbauer spectrum of NP Fe₃O₄ prepared from hydrothermal reaction was composed of two sextets with absorption area (A), isomer shift (δ) and internal magnetic field (H _int) of 56.3 %, 0.34_±0.03 mm s^???1 and 49.0_±0.30 T for tetrahedral (T _d) Fe^III, and 43.7 %, 0.66_±0.11 mm s^???1 and 44.0_±0.71 T for octahedral (O _h) Fe^II?+?III. The Fe^II/Fe^III ratio was determined to be 0.280 for NP Fe₃O₄, giving ‘x’ of 0.124 in Fe_3???xO_4. These results show that NP Fe₃O₄ prepared by hydrothermal reaction was not regular but nonstoichiometric Fe₃O₄. Consistent results were observed for XRD patterns of NP Fe_3???xO₄ indicating sharp intense peaks at 2Θ of 30.2, 35.7 and 43.3° with a large linewidth of 0.44°, yielding the crystallite size of 29–37 nm from the Scherrer’s equation. Iso-thermal annealing of NP Fe_3???xO₄ at 250 °C for 30 min resulted in the precipitation of NP γFe₂O₃ with δ of 0.33_±0.03 mm s^???1 and H _intof 46.4_±0.27 T due to magnetic tetrahedral Fe^III. The Debye temperature of NP Fe_3???xO₄ was respectively estimated to be 267_±5.45 K for Fe $^{\mathrm{III}}(T_{\mathrm{d}})$ and 282_±7.17 K for Fe $^{\mathrm{II+III}}(O_{\mathrm{h}})$ , both of which were smaller than that obtained for bulk Fe₃O₄ of 280_±4.15 K and 307_±5.70 K, indicating that the chemical environment of iron of NPs is less rigid than that of the bulk compounds. A leaching test using methylene blue (MB) and mixture of bulk Fe⁰-NP γFe₂O₃ (3:7) showed a remarkable decrease in MB concentration from 1.90 × 10^???2 to 9.49 × 10^???4 mM for 24 h with the first order rate constant (k _MB) of 2.1 × 10^???3 min^???1. This result verifies that MB decomposing ability is enhanced by using NP γFe₂O₃ compared with the k _MB of 1.1 × 10^???4 min^???1 previously obtained from the leaching test using MB and bulk mixture of Fe⁰???γFe₂O₃ (3:7).     

Role of Al2O3 in upconversion and NIR emission in Tm and Er codoped calcium fluoro phosphorous silicate glass system

In this study, the principal role of Al₂O₃ on the features of the photoluminescence spectra of Tm³⁺ ion and upconversion phenomenon in Tm³⁺ and Er³⁺ codoped CaF₂−Al₂O₃−P₂O₅−SiO₂ glass system has been investigated. The concentration of Al₂O₃ is varied from 2 to 10 mol% while that of Er³⁺ and Tm³⁺ is fixed. IR and Raman spectral studies have indicated that there is a gradual increase in the degree of disorder in the glass network with increase in the concentration of Al₂O₃ up to 6.0 mol%. This is attributed to the presence of Al³⁺ ions in octahedral positions in larger proportions. When the glasses are doped with Tm³⁺ ions, the blue and red emissions were observed, whereas in Er³⁺ doped glasses blue, green and red emissions were observed. When the glasses are codoped with Tm³⁺ and Er³⁺ ions and excited at 790 nm, all the three emission lines were observed to be reinforced, especially in the glasses mixed with 6.0 mol% of Al₂O₃. The IR emission band detected at about 1.8 μm due to ³F₄→³H₆ transition of Tm³⁺ ions is also observed to be strengthened due to codoping. The reasons for enhancement in the intensity of various emission bands due to codoping have been identified and discussed with the help of rate equations for various emission transitions.     

Study on the ferromagnetic state in iron mixed-valence complexes, A[FeIIFeIII(dto)3] (A = (n-CnH2n + 1)4N; dto = C2S2O2) by means of Mössbauer spectroscopy

We have investigated the ferromagnetic states for (n-C_nH_2n?+?1)₄N[Fe^IIFe^III(dto)₃] (n = 3–6; dto = C₂O₂S₂) by means of ⁵⁷Fe Mössbauer spectroscopy. The major component of the spin configuration in the ferromagnetic states for n = 3 and 4 is the low-temperature phase (LTP) with the Fe^III (S = 5/2) and Fe^II (S = 0) states. The high-temperature phase (HTP) of n = 4 remains by more than 20%, which is consistent with two ferromagnetic transitions (T_C = 7 & 13 K). Moreover, it was revealed that the Mössbauer spectra in the ferromagnetic states for n = 5 and 6 correspond to the HTP consisting of the Fe^II (S = 2) and Fe^III (S = 1/2) states.     

Visible light activated photo-catalytic effect and local structure of iron silicate glass prepared by sol-gel method

A relationship between methylene blue (MB) decomposition ability under visible light and local structure of xFe₂O₃·(100-x)SiO₂ glass abbreviated as xFS prepared by sol-gel method was investigated by ⁵⁷Fe-Mössbauer spectroscopy, X-ray diffractometry (XRD) and ultraviolet-visible light absorption spectroscopy (UV-Vis). Mössbauer spectra of xFS glass with x of 10, 30 and 50 annealed at 1000 °C for 3 h were mainly composed of a paramagnetic doublet due to fayalite (Fe₂SiO₄), and magnetic sextets due to magnetite (Fe₃O₄) or hematite (α-Fe₂O₃). The absorption area (A) of α-Fe₂O₃ gradually increased from 0.0 to 10.3 and 100 % with the increasing Fe₂O₃ content (x) of annealed xFS glass. A leaching test performed by 20 mL of MB aqueous solution and 40 mg of annealed 50FS glass showed that MB concentration decreased from 16.2 to 4.7 μmol L^?1 after 2 h with the first order rate constant of 1.8 × 10^?4 s^?1. These results prove that annealed iron silicate glass containing α-Fe₂O₃ can decompose MB effectively under visible light irradiation.