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.     

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.     

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.     

Mössbauer study of new vanadate glass with large charge-discharge capacity

Charge-discharge capacity and cyclicity of lithium ion battery (LIB) was evaluated in which 15Li₂O·10Fe₂O₃·xSnO₂·5P₂O₅·(70–x)V₂O₅ glass (x?=?0 and 20 in mol%, abbreviated as xLFSPV) was used as a cathode. A local structure of xLFSPV glass before and after charging was investigated by ⁵⁷Fe- and ¹¹⁹Sn-Mössbauer spectroscopies. ⁵⁷Fe-Mössbauer spectrum of xLFSPV glass with ‘x’ of 20 was composed of a doublet with isomer shift (δ) of 0.35_±0.02 mm s^???1 and quadrupole splitting (Δ) of 0.88_±0.03 mm s^???1 due to distorted Fe^IIIO₄ tetrahedra. ¹¹⁹Sn-Mössbauer spectrum of this glass consisted of a doublet with δ of 0.08_±0.01 and Δ of 0.52_±0.01 mms^???1 due to distorted Sn^VIO₆ octahedra. After discharging the battery from 4.5 to 1.0 V, larger δ of 0.40_±0.03 mm s^???1 and Δ of 0.94_±0.04 mm s^???1 were obtained, indicating that both iconicity of Fe-O bonds and local distortion of Fe^IIIO₄ tetrahedra were increased. On the contrary, identical δ of 0.09_±0.01 mm s^???1 and Δ of 0.50_±0.01 mm s^???1 were observed in the ¹¹⁹Sn-Mössbauer spectrum of 20LFSPV glass after the discharge, indicating that chemical environment of Sn^IVO₆ octahedra was not affected after the discharge. Charge-discharge curve of LIB containing 20LFSPV glass as a cathode active material recorded under the current density of 8.3 mA g^???1 (0.011 mA cm^???2) between 1.0 and 4.5 V showed a large initial charge capacity of 431.1 mAh g^???1 and discharge capacity of 382.3 mAh g^???1, respectively. These results indicate that 20LFSPV glass could be a new cathode active material for LIB.     

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).     

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.     

Dissolution behaviour of iron silicate glass

A relationship between the water purifying effect and structure of 0.5xNa₂O·0.5xCaO·5Fe₂O₃·(95–x)SiO₂ glass (Na₂O/CaO = 1; NCFS glass) with ‘x’ of 20 and 50 were investigated by means of ⁵⁷Fe-Mössbauer spectroscopy, X-ray diffraction (XRD), induced coupled plasma optical emission spectroscopy (ICP-OES), as well as absorption spectroscopy, pH and oxidation-reduction potential (ORP) measurements. In the case NCFS glass with ‘x’ of 20, dissolved amounts of total Fe, Na^?+?, and Ca^2?+? were respectively estimated to be 13.6, 39.1 and 36.7 mg/l, after 10 day-leaching test. On the other hand, the dissolved amounts of total Fe, Na^?+? and Ca^2?+? were determined to be 34.3, 647.6 and 667.6 mg/l, respectively when ‘x’ was 50. The original pH value of 6.0 was increased to 10.0 and 11.6 after leaching test of NCFS glasses with ‘x’ of 20 and 50, respectively. At the same time, the ORP value was decreased from 30.0 to ?195.8 and ?284.7 mV in the glasses with ‘x’ of 20 and 50, respectively.     

Decomposition mechanism of methylene blue caused by metallic iron-maghemite mixture

Decomposition mechanism of methylene blue (MB) caused by a mixture of metallic iron-maghemite (Fe⁰-γFe₂O₃) was investigated by means of ⁵⁷Fe-Mössbauer spectroscopy, X-ray diffractometry (XRD), Ultraviolet-Visible Absorption Spectroscopy (UV-vis) and electrospray-ionization mass spectroscopy (ESI-MS). Ten day-leaching test of 10 μmol L^???1 MB aqueous solution and Fe⁰-γFe₂O₃ mixture (mass ratio 3:7) showed a decrease in the concentration from 10.5 to 4.45 μmol L^???1 with first-order rate constant (k) of $1.5_{7} \times 10^{-1}$  day^???1. An ESI-MS study of Fe⁰-γFe₂O₃ mixture (3:7) after the leaching test revealed new peaks at m/z of 100, 110 and 137 due to fragmentation of MB, in addition to those observed at m/z of 284, 270 and 256 which were ascribed to MB, Azure B and Azure A, respectively. ⁵⁷Fe-Mössbauer spectra of Fe⁰-γFe₂O₃ mixture (3:7) resulted in a decrease in absorption area (A) for Fe⁰ (δ?=?0.00_±0.01 mm s^???1, H _int?=?33.0_±0.1 T) from 37.5 to 21.3, 9.7, 7.9, 7.0 and 4.5_±0.5 %, together with an increase in A from 0.0 to 5.0, 13.8, 17.2, 21.0 and 22.4_±0.5 % for octahedral (O _h) iron (Fe^II?+?Fe^III) of Fe₃O₄. XRD study of these samples indicated that the peak intensity at 2Θ of 44.7° being ascribed to Fe⁰ was decreased, while that of 35.6° due to Fe₃O₄ was almost constant; relative peak ratio of Fe $^{0}/\mathrm{Fe}_{3}$ O₄ was decreased from 26.3 to 2.76 after the leaching, indicating that Fe⁰ in the Fe⁰-γFe₂O₃ mixture was oxidized to Fe₃O₄. These experimental results suggest that Fe⁰-γFe₂O₃ mixture could be utilized for the cleaning or decomposition of toxic organic compounds like trichloroethylene.     

Mössbauer investigation of iron uptake in wheat

Iron uptake and distribution in wheat roots were studied with ⁵⁷Fe Mössbauer spectroscopy. Plants were grown both in iron sufficient and in iron deficient nutrient solutions. Mössbauer spectra of the frozen iron sufficient roots exhibited three iron(III) components with the typical average Mössbauer parameters of δ?= 0.50 mm s^???1, Δ?= 0.43 mm s^???1, δ?= 0.50 mm s^???1, Δ?= 0.75 mm s^???1 and δ?= 0.50 mm s^???1, Δ?= 1.20 mm s^???1 at 80 K. These doublets are very similar to those obtained earlier for cucumber [0], which allows us to suppose that iron is stored in a very similar way in different plants. No ferrous iron could be identified in any case, not even in the iron deficient roots, which confirms the mechanism proposed for iron uptake in the graminaceous plants.     

EPR and magnetic susceptibility studies of iron ions in ZnO-Fe2O3-SiO2-CaO-P2O5-Na2O glasses

Room temperature electron paramagnetic resonance (EPR) spectra and temperature dependent magnetic susceptibility data have been obtained on bulk x(ZnO,Fe₂O₃)(65−x)SiO₂20(CaO, P₂O₅)15Na₂O (6≤x≤21 mole%) glasses prepared by melt quenching method. EPR spectra of the glasses revealed absorptions centered at g≈2.1 and 4.3. The variations of the intensity and line width of these absorption lines with composition have been interpreted in terms of the variation in the concentration of the Fe²⁺ and Fe³⁺ ions in the glass and the interaction between the iron ions. EPR and magnetic susceptibility data of the glasses reveal that both Fe²⁺ and Fe³⁺ ions are present in the glasses, with their relative concentration being dependent on the glass composition. The studies reveal superexchange type interactions in these glasses, which are strongly dependent on their iron content.     

Part II: Effect of high energy proton beam fluence on the electrical studies of lithium gallium phosphate glass electrolyte doped with selenium ions

A series of glass samples, according to the formula (100 ? x) (0.5Li₂O ? 0.2Ga₂O₃ ? 0.3P₂O₅) + xSeO₂ (x?=?0, 2, 4, 6, 8, 10) and 12 mol.%, labeled as LGPS _x (x is the mole percent of SeO₂), were synthesized through melt quenching technique. All the LGPS _x samples were irradiated by a high energy proton (H⁺) beam of 3 MeV at fluence of 10¹⁴, 5 × 10¹⁴, and 10 × 10¹⁴ ions/cm². FTIR and Raman spectra indicated that SeO₂ acts either as a glass modifier (SeO ₃ ^2? ) or a glass former (SeO ₄ ^2? ), as the dose rate of beam fluence changes. The bulk conductivity of the highest conducting sample LGPS₁₀ irradiated at a beam fluence of 5 × 10¹⁴ ions/cm² was determined as 5.87 × 10^?04 S/cm at 303 K. The super curve in the normalized spectra of electrical modulus at different temperatures confirms that the LGPS samples follow the temperature-independent, frequency-dependent relaxation time before and after irradiation.     

Conductivity and spectroscopic studies of Li<Subscript>2</Subscript>O-V<Subscript>2</Subscript>O<Subscript>5</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

Lithium vanadium-borate glasses with the composition of 0.3Li₂O–(0.7-x)B₂O₃–xV₂O₅ (x?=?0.3, 0.325, 0.35, 0.375, 0.4, 0.425, 0.45, and 0.475) were prepared by melt-quenching method. According to differential scanning calorimetry data, vanadium oxide acts as both glass former and glass modifier, since the thermal stability of glasses decreases with an increase in V₂O₅ concentration. Fourier transform infrared spectroscopy data show that the vibrations of [VO₄] structural units occur at V₂O₅ concentration of 45 mol%. It is established that the concentration of V⁴⁺ ions increases exponentially with the growth of vanadium oxide concentration. Direct and alternative current measurements are carried out to estimate the contribution both electronic and ionic conductivities to the value of total conductivity. It is shown that the electronic conductivity is predominant in the total one. The glass having the composition of 0.3Li₂O-0.275B₂O₃-0.475V₂O₅ shows the highest electrical conductivity that has the value of 7.4?×?10^?5 S cm^?1 at room temperature.     

Dimeric Fe (II, III) complex of quinoneoxime as functional model of PAP enzyme: Mössbauer, magneto-structural and DNA cleavage studies

Purple acid phosphatase, (PAP), is known to contain dinuclear Fe₂ ^?+?2,?+?3 site with characteristic Fe^?+?3 ← Tyr ligand to metal charge transfer in coordination. Phthiocoloxime (3-methyl-2-hydroxy-1,4-naphthoquinone-1-oxime) ligand L, mimics (His/Tyr) ligation with controlled and unique charge transfers resulting in valence tautomeric coordination with mixed valent diiron site in model compound Fe-1: [μ-OH-Fe₂ ^?+?2,?+?3 (o-NQ_CH3ox) (o-NSQ_CH3ox)₂ (CAT) H₂O]. Fe-2: [Fe^?+?3(o-NQ_CH3ox) (p-NQ_CH3ox)₂]₂ a molecularly associated dimer of phthiocoloxime synthesized for comparison of charge transfer. ⁵⁷Fe Mössbauer studies was used to quantitize unusual valences due to ligand in dimeric Fe-1 and Fe-2 complexes which are supported by EPR and SQUID studies. ⁵⁷Fe Mössbauer spectra for Fe-1 at 300 K indicates the presence of two quadrupole split asymmetric doublets due to the differences in local coordination geometries of [Fe^?+?3]_A and [Fe^?+?2]_B sites. The hyperfine interaction parameters are δ _A = 0.152, (ΔE _Q)_A = 0.598 mm/s with overlapping doublet at δ _B = 0.410 and (ΔE _Q)_B = 0.468 mm/s. Due to molecular association tendency of ligand, dimer Fe-2 possesses 100% Fe^?+?3(h.s.) hexacoordinated configuration with isomer shift δ = 0.408 mm/s. Slightly distorted octahedral symmetry created by NQ_CH3ox ligand surrounding Fe^?+?3(h.s.) state generates small field gradient indicated by quadrupole split ΔE _Q = 0.213 mm/s. Decrease of isomer shifts together with variation of quadrupole splits with temperature in Fe-1 dimer compared to Fe-2 is result of charge transfers in [Fe₂ ^?+?2,?+?3 SQ] complexes. EPR spectrum of Fe-1 shows two strong signals at g ₁ = 4.17 and g ₂ = 2.01 indicative of S = 3/2 spin state with an intermediate spin of Fe^?+?3(h.s.) configuration. SQUID data of $\chi _m^{{\rm corr}} \mbox{.T}$ were best fitted by using HDVV spin pair model S = 2, 3/2 resulting in antiferromagnetic exchange (J = ?13.5 cm^???1 with an agreement factor of R = 1.89 × 10^???5). The lower J value of antiferromagnetic exchange leads to Fe⁺³μ-(OH) Fe^?+?2 bridging in Fe-1 dimer instead of μ-oxo bridge. The intermolecular association through H-bonds may lead to weakly coupled antiferromagnetic interaction between two Fe-2 molecules having Fe^?+?3(h.s.) centers. Using S = 5/2, 5/2 spin pair model we obtained best-fitted parameters such as J = ?12.4 cm^???1, g = 2.3 with R = 3.58 × 10^???5. Synthetic strategy results in non-equivalent iron sites in Fe-1 dimer analogues to PAP enzyme hence its reconstitution results in pUC-19 DNA cleavage activity, as physiological functionality of APase. It is compared with nuclease activity of Fe-2 RAPase.     

Photochromic and electrochromic properties of tungstate glasses

Electrochromic and photochromic behavior have been observed for the first time in the Li₂O-B₂O₃-WO₃ glass system. Double injection of protons and electrons results in the formation of H_xWO₃ in the glass matrix which exhibits a broad absorption band peaking in the vicinity of 1.45–1.65 eV due to electron hopping between W⁺⁵ and W⁺⁶ sites. An electron diffusion coefficient of D_e∽3×10^-6cm²sec^-1 has been measured near the percolation threshold when the volume filling fraction f > 0.3 for WO₃ in the glass matrix. The electrochemical potential of these tungstate glasses varies as a function of coloration.     

Mössbauer characterization of Fe-doped ZnO prepared by mechanical milling

The preparation of massive oxides Zn₁??? _x Fe _x O by means of mechanical milling in diverse gaseous atmospheres and starting with different powder mixtures was investigated. ZnO powder with 10 at.% admixture of Fe, FeO or Fe₂O₃, were milled during 1, 4 or 16 h and characterized by X-ray diffraction and Mössbauer spectroscopy. Different phases were obtained according to the initial conditions (precursor used, atmosphere, etc.) and phase’s formation enthalpies.     

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.     

Role of WO3 in structural and optical properties of WO3-Al2O3-PbO-B2O3 glasses

Glass samples of composition xAl₂O₃-20PbO-(80−x)B₂O₃ and xWO₃-xAl₂O₃-20PbO-(80−2x)B₂O₃ with x varying from 0% to 10% mole fraction are prepared by melt quench technique. The optical band gap decreases (from 3.21 to 2.37 eV) more for WO₃-Al₂O₃-PbO-B₂O₃ glasses with an addition of WO₃ content. The FTIR spectral studies have pointed out the conversion of structural units of BO₃ to BO₄ and WO₄ to WO₆ in these glasses. The increase in density from 4.51 to 5.80 g cm⁻³ for WO₃-Al₂O₃-PbO-B₂O₃ glasses is observed with an increase in WO₃ content. This is observed that the atomic structure changes more with the incorporation of WO₃. This is due to the formation of WO₆, WO₄ and BO₄ units.     

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.     

Observation of spin-lattice relaxations of dilute Fe3+ in MgO by Mössbauer spectroscopy

We present a method to describe the temperature dependence of emission Mössbauer spectra showing slow spin-lattice relaxations of Fe^3?+? in MgO single crystals, obtained after implantation of ⁵⁷Mn at ISOLDE/CERN. The analysis is based on the Blume-Tjon model for the line-shape of relaxing paramagnetic sextets with the spin relaxation rate, τ ^???1 as a parameter. The temperature dependent spin relaxation rate of Fe^3?+? in MgO is found to increase to ~10⁸ s^???1 at 647 K by assuming a relaxation rate of τ ^???1?< 10⁶ s^???1 at 77 K. The results are in accordance with those obtained by electron paramagnetic resonance spectroscopy demonstrating the possibility of retrieving spin-lattice relaxation rates of dilute Fe^3?+? from emission Mössbauer spectroscopy of Mn/Fe-implanted oxides.     

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.