The structure of WO 3-TeO 2 glasses containing 15, 20 and 25 mol% WO 3 are studied by neutron dif... more The structure of WO 3-TeO 2 glasses containing 15, 20 and 25 mol% WO 3 are studied by neutron diffraction (ND), high energy X-ray diffraction (XRD) and X-ray Absorption Near Edge spectroscopy (XANES). The short-range structural properties of glasses i.e. TeeO and WeO speciation, coordination number distributions, bond-lengths, and the OeTeeO, OeWeO and OeOeO bond angle distributions in the glass network are determined by the Reverse Monte Carlo (RMC) simulations of the ND and XRD data. RMC technique successfully determined all partial pair correlation functions and the coordination number distributions revealed that glass network consists predominantly of TeO 4 and WO 4 units with small amounts of triangular, penta and hexa coordinated units. The average WeO and TeeO bond lengths are in the ranges: 1.69–1.75 ± 0.01 Å and 1.99–2.00 ± 0.01 Å respectively. Both WeO and TeeO correlation peaks are asymmetrical, that indicate a distribution of their bond lengths in the respective structural units. The O-Te-O bond angle distribution has a peak at 107 ± 2°. Similarly the O-W-O bond angle distribution has a peak at 108 ± 5°. On increasing the WO 3 concentration from 15 to 25 mol%, the average TeeO coordination number decreases from 3.80 to 3.61 ± 0.02 due to the structural transformation: TeO 4 → TeO 3 , similarly the WeO coordination also decreases and is in the range: 3.79–3.67 ± 0.02. XANES studies found that the oxidation state of Te and W ions in the glasses are 4 + and 6 + respectively.
A B S T R A C T Glass and anti-glass samples of Bi 2 O 3-TeO 2 and Bi 2 O 3-Nb 2 O 5-TeO 2 were p... more A B S T R A C T Glass and anti-glass samples of Bi 2 O 3-TeO 2 and Bi 2 O 3-Nb 2 O 5-TeO 2 were prepared by ice-water quenching and normal-quenching respectively. The bismuth tellurite system has poor glass forming ability (GFA) and forms a glassy phase at low Bi 2 O 3 concentration of 2 to 5-mol%. On increasing Bi 2 O 3 concentration to 10 mol%, a mixture of glass and anti-glass phases are formed by rapid quenching of the melt. A further increase in Bi 2 O 3 concentration to 20 mol%, produces a sample consisting of entirely Bi 2 Te 4 O 11 anti-glass upon melt-quenching. An anti-glass is a solid, which has long range order of cations (Te 4+ , Bi 3+ , Nb 5+ etc.) but these are statistically distributed at their sites while the anion sites are partially vacant. Consequently the X-ray diffraction (XRD) patterns of bismuth tellurite and bismuth niobium tellurite anti-glass samples show sharp XRD peaks but the Raman spectra show broad phonon bands due to disturbed short-range order of the anions. The addition of Nb 2 O 5 to the Bi 2 O 3-TeO 2 system significantly enhances the GFA. Samples from the system: xBi 2 O 3-xNb 2 O 5-(100-2x)TeO 2 grow micro-inclusions or spherulites of size of several micron within the glass matrix on slow melt-cooling. Heat treatment of 7.5Bi 2 O 3-7.5Nb 2 O 5-85TeO 2 sample show structural transitions from glass→ anti-glass →crystalline phases.
A B S T R A C T BaO-TeO 2 glasses containing 10 to 20-mol% BaO were studied by X-ray diffraction,... more A B S T R A C T BaO-TeO 2 glasses containing 10 to 20-mol% BaO were studied by X-ray diffraction, density, thermal analysis, UV–visible and Raman spectroscopy. The effects of Eu 3 + , Dy 3 + , Er 3 + and Nd 3 + on the density, thermal, optical absorption and luminescent properties of barium tellurite glasses were studied. The short-range structure of barium tellurite glasses consists of TeO 4 trigonal bipyramidal and TeO 3 trigonal pyramidal units. TeeO coordination (N TeeO) was determined by Raman studies; it was found that that N TeeO decreases with increase in BaO and rare earth oxide concentration. The glass transition temperature is a function of both the average single bond enthalpy and non-bridging oxygen concentration in the glass network. Glasses containing Dy 3 + and Eu 3 + show strong visible light photoluminescence, and our results show that barium tellurite glasses are suitable hosts for rare earth ion luminescence due to low phonon energies.
Keywords: V2O5 thin films Thermo-optical effect XRR GIXRD Optical properties Raman spectra a b s ... more Keywords: V2O5 thin films Thermo-optical effect XRR GIXRD Optical properties Raman spectra a b s t r a c t Crystalline V 2 O 5 films of thicknesses in the range: 78–119 nm were prepared on glass sub-strates by thermal evaporation with in-situ substrate heating at 350 • C. XRD studies found the growth of highly oriented orthorhombic V 2 O 5 films with two peaks corresponding to (001) and (002) crystal planes. Raman studies also confirmed the formation of orthorhom-bic V 2 O 5 phase. Electrical studies by two-probe study showed an increase in conductivity with temperature indicating the semiconducting nature of the samples. Optical studies found that UV–vis transmittance is maximum and the reflectance is minimum in film with lowest thickness. The values of activation energy for conduction are 0.15 eV, 0.16 eV and 0.19 eV and those of optical band gap are 2.85 eV, 2.63 eV and 2.67 eV for films of thicknesses: 78 nm, 88 nm and 119 nm respectively. Grazing incidence X-ray reflectivity studies on the film samples showed that the surface roughness increases with increase in thickness and that the density of the samples is 70.6% of that of the bulk V 2 O 5. In-situ high temperature Raman studies up to 60 • C found that the Raman bands at 283 cm −1 and 305 cm −1 broaden considerably and decrease in intensity with increase in temperature; these bands however recover their original shape on cooling. Both peak broadening and recovery effects occur with time lag of ∼30 min and ∼20 min respectively. A decrease in average UV–vis-NIR transmission of ∼1% was observed with increase in temperature, and this thermo-optical effect is reversible.
Tellurite and borotellurite glasses containing Bi 2 O 3 and TiO 2 were prepared and structure-pro... more Tellurite and borotellurite glasses containing Bi 2 O 3 and TiO 2 were prepared and structure-property correlations were carried out by density measurements, X-ray diffraction, Differential Scanning Calorimetry (DSC), Raman, FTIR, UV–visible and 11 B MAS-NMR studies. Titanium-tellurite and titanium bismuth tellurite glasses require high melt-cooling rates and were prepared by splat quenching. On adding B 2 O 3 , the glass forming ability (GFA) enhances considerably and bulk glasses could be synthesized at lower quenching rates. The density of glasses shows a direct correlation with molecular mass of the constituents. UV–visible studies were used to determine the optical band gap and refractive index. Raman studies found that the coordination number of tellurium ions with oxygen (N TeeO) remains constant with variation in TiO 2 molar content, while the incorporation of B 2 O 3 and Bi 2 O 3 decreases N TeeO. DSC studies show that the glass transition temperature (T g) increases with B 2 O 3 and TiO 2 concentrations and that T g correlates well with bond enthalpy of the metal oxides. 11 B MAS-NMR studies found that the coordination number of boron with oxygen (N BeO) decreases with increase in B 2 O 3 content while increasing TiO 2 and Bi 2 O 3 concentration does not significantly modify N BeO .
A B S T R A C T Alumino-tellurite glasses with wide range of Al 2 O 3 concentration (1 to 20-mol%... more A B S T R A C T Alumino-tellurite glasses with wide range of Al 2 O 3 concentration (1 to 20-mol%) are prepared and their short-range structural and thermal properties are studied by Raman spectroscopy, 27 Al Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) and Differential Scanning Calorimetry (DSC). Glass sample with 1-mol% of Al 2 O 3 has TeeO coordination of 3.66, which is close to the value of 3.68 reported in pure TeO 2 glass. TeeO coordination decreases steadily to 3.33 on increasing alumina content to 20-mol%. 27 Al MAS-NMR studies found that Al ions exist in hexa, penta and tetrahedral coordination in the alumino-tellurite network. On increasing alumina content from 3 to 20-mol%, the concentration of hexa-coordinated AleO units decreases from 54% to 35% with a simultaneous increase in the concentration of penta and tetra coordinated AleO units. Glass transition temperature increases with increase in Al 2 O 3 concentration and correlates directly with the average single bond enthalpy of the glass network.
Tellurite and borotellurite glasses containing Bi 2 O 3 and TiO 2 were prepared and structure-pro... more Tellurite and borotellurite glasses containing Bi 2 O 3 and TiO 2 were prepared and structure-property correlations were carried out by density measurements, X-ray diffraction, Differential Scanning Calorimetry (DSC), Raman, FTIR, UV–visible and 11 B MAS-NMR studies. Titanium-tellurite and titanium bismuth tellurite glasses require high melt-cooling rates and were prepared by splat quenching. On adding B 2 O 3 , the glass forming ability (GFA) enhances considerably and bulk glasses could be synthesized at lower quenching rates. The density of glasses shows a direct correlation with molecular mass of the constituents. UV–visible studies were used to determine the optical band gap and refractive index. Raman studies found that the coordination number of tellurium ions with oxygen (N TeeO) remains constant with variation in TiO 2 molar content, while the incorporation of B 2 O 3 and Bi 2 O 3 decreases N TeeO. DSC studies show that the glass transition temperature (T g) increases with B 2 O 3 and TiO 2 concentrations and that T g correlates well with bond enthalpy of the metal oxides. 11 B MAS-NMR studies found that the coordination number of boron with oxygen (N BeO) decreases with increase in B 2 O 3 content while increasing TiO 2 and Bi 2 O 3 concentration does not significantly modify N BeO .
Alumina coatings have been deposited on glass substrates by reactive ac (41 kHz) magnetron sputte... more Alumina coatings have been deposited on glass substrates by reactive ac (41 kHz) magnetron sputtering of two hollow aluminum targets in argon-oxygen plasma at 5 kW sputtering power in the poisoned mode and in the unstable region of hysteresis loop of reactive sputtering. The poisoned mode produces nanocrystalline films of γ and δ alumina at a low deposition rate of 0.06 nm·s-1. Amorphous alumina films have been grown at a higher deposition rate of 0.2 nm·s-1 with the aid of optical emission spectroscopy in which the feedback signal of Al emission spectral line at 396 nm monitored Al concentration in the plasma discharge and accomplished the controlled oxidation of targets during reactive sputtering. Dynamic secondary ion mass spectroscopy studies confirm that alumina films grown in the unstable region of the hysteresis loop of reactive sputtering are highly stoichiometric and of uniform composition with film thickness. Our study demonstrates the successful coupling of optical emission spectroscopy with hollow cylindrical magnetrons for deposition of alumina films.
Bismuth tellurite and bismuth borotellurite samples were synthesized and structure-property corre... more Bismuth tellurite and bismuth borotellurite samples were synthesized and structure-property correlations were carried out by density, X-ray diffraction, dielectric measurements, differential scanning calorimetry, infrared, Raman and 11 B Magic Angle Spinning Nuclear Magnetic Resonance studies. Low concentration of Bi 2 O 3 (5-mol %) forms bismuth tellurite glass while higher concentration of Bi 2 O 3 (10 and 20-mol%) produces anti-glasses on splat-quenching the melt. The short-range structure of bismuth borotellurite glasses consists of TeO 4 , TeO 3 , BO 4 and BO 3 structural units. Raman studies show that TeeO coordination (N TeeO) in bismuth tellurite glass and anti-glass samples decreases from 3.48 to 3.43 with increase in Bi 2 O 3 concentration from 5 to 20-mol%. On incorporating 20-mol% of B 2 O 3 into bismuth tellurite sample, N TeeO decreases to 3.33 and the glass forming ability enhances significantly as compared to that of bismuth tellurite system. On increasing B 2 O 3 upto 40-mol%, the BeO coordination decreases steadily. The addition of Bi 2 O 3 produces the structural transformation: TeO 4 → TeO 3 in Bi 2 O 3-TeO 2 system while B 2 O 3 produces the structural transformation: BO 4 → BO 3 in Bi 2 O 3-B 2 O 3-TeO 2 series without significantly modifying N TeeO. The glass transition temperature increases from 371 °C to 410 °C on increasing B 2 O 3 from 20 to 40-mol%, this increase is due to increase in the concentration of stronger BeO linkages at the expense of weaker TeeO bonds. Decrease in the dielectric constant from 24.1 to 19.3 with B 2 O 3 concentration is due to decrease in density while the polarizability of bismuth borotellurite series remains constant.
A B S T R A C T Alumino-tellurite glasses with wide range of Al 2 O 3 concentration (1 to 20-mol%... more A B S T R A C T Alumino-tellurite glasses with wide range of Al 2 O 3 concentration (1 to 20-mol%) are prepared and their short-range structural and thermal properties are studied by Raman spectroscopy, 27 Al Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) and Differential Scanning Calorimetry (DSC). Glass sample with 1-mol% of Al 2 O 3 has TeeO coordination of 3.66, which is close to the value of 3.68 reported in pure TeO 2 glass. TeeO coordination decreases steadily to 3.33 on increasing alumina content to 20-mol%. 27 Al MAS-NMR studies found that Al ions exist in hexa, penta and tetrahedral coordination in the alumino-tellurite network. On increasing alumina content from 3 to 20-mol%, the concentration of hexa-coordinated AleO units decreases from 54% to 35% with a simultaneous increase in the concentration of penta and tetra coordinated AleO units. Glass transition temperature increases with increase in Al 2 O 3 concentration and correlates directly with the average single bond enthalpy of the glass network.
Laser direct write of silver nanoparticles from solution onto glass substrates for surface-enhanc... more Laser direct write of silver nanoparticles from solution onto glass substrates for surface-enhanced Raman spectroscopy Appl. Phys. Lett. 91, 023107 (2007); 10.1063/1.2753090 Surface enhanced Raman scattering of p-aminothiophenol self-assembled monolayers in sandwich structure fabricated on glass
Thermoelastic and texture behavior of aluminum at high pressure and high temperature investigated... more Thermoelastic and texture behavior of aluminum at high pressure and high temperature investigated by in situ neutron diffraction J. Appl. Phys. 95, 4645 (2004); 10.1063/1.1688460 High‐pressure in situ investigation of cubanite (CuFe2S3): Structural phase transition Abstract. Synchrotron based angle dispersive x−ray diffraction (ADXRD) studies were performed on metastable crystalline bismuth orthoborate (BiBO 3) up to 14.5 GPa during compression and decompression cycle. These studies revealed that the BiBO 3 is unstable and it converts to Bi 4 B 2 O 9 phase at high pressure. Moreover the transformation is found to be irreversible.
Tungsten trioxide (WO 3) thin films were deposited on silica, silicon and alumina substrates and ... more Tungsten trioxide (WO 3) thin films were deposited on silica, silicon and alumina substrates and their crystal structure, surface morphology, optical and gas-sensing properties were compared with those of WO 3 nanoparticles. As-deposited films were amorphous and crystallized into the mon-oclinic phase with heat treatment. Raman spectroscopy revealed that the short-range structure of amorphous, crystalline films and nanoparticles of WO 3 are similar, but the amorphous phase contain W 6+ = O terminal bonds that do not exist in bulk and nanocrystalline samples. Raman studies confirmed that amorphous samples contain higher concentration of hydrogen and hydroxyl ion impurities, which affect the optical bandgap. Thin films show a response of 3 for 150 ppm of H 2 S and 7 for 2000 ppm of C 2 H 5 OH. Platelet shaped nanoparticles exhibit higher response of 37 and fast response and recovery times of 1 to 2 min for 150 ppm of H 2 S.
ABSTRACT Thin films of amorphous alumina were prepared on fused silica substrates by e-beam evapo... more ABSTRACT Thin films of amorphous alumina were prepared on fused silica substrates by e-beam evaporation technique without any deliberate substrate heating. The effects of thermal annealing of alumina films on the structural and optical properties were investigated for annealing temperatures of 600°C, 800°C, 950°C, 1050°C and 1130°C. The present study focuses on investigating the thermal and mechanical stability of the films and phase and structural transformations as a function of heat treatment. With increasing temperature, different crystallographic phases were observed to grow in the films. The most dominant phases were γ and δ alumina which were stable upto 1100°C. Optical properties of the films were measured by UV-visible optical spectroscopy and refractive index value was measured to be 1.66 +/- 0.01 for an amorphous film. The refractive index increased to 1.78 +/- 0.01 (at a wavelength of 700 nm) on crystallization of amorphous coatings.
The mass attenuation coefficient, the effective atomic number and the effective electron density ... more The mass attenuation coefficient, the effective atomic number and the effective electron density are basic quantities for determining the penetration of gamma-ray photons in matter. Tabulations of mass attenuation coefficients and interaction cross sections have been published eg, ...
Tungsten trioxide (WO 3) thin films were deposited on silica, silicon and alumina substrates and ... more Tungsten trioxide (WO 3) thin films were deposited on silica, silicon and alumina substrates and their crystal structure, surface morphology, optical and gas-sensing properties were compared with those of WO 3 nanoparticles. As deposited films were amorphous and crystallized into the mon-oclinic phase with heat treatment. Raman spectroscopy revealed that the short-range structure of amorphous, crystalline films and nanoparticles of WO 3 are similar, but the amorphous phase contain W 6+ = O terminal bonds that do not exist in bulk and nanocrystalline samples. Raman studies confirmed that amorphous samples contain higher concentration of hydrogen and hydroxyl ion impurities, which affect the optical bandgap. Thin films show a response of 3 for 150 ppm of H 2 S and 7 for 2000 ppm of C 2 H 5 OH. Platelet shaped nanoparticles exhibit higher response of 37 and fast response and recovery times of 1 to 2 min for 150 ppm of H 2 S.
The effects of addition of Al3+, W6+, Nb5+ and Pb2+ on the density, thermal, optical properties o... more The effects of addition of Al3+, W6+, Nb5+ and Pb2+ on the density, thermal, optical properties of borotellurite glasses and on the B-O, Te-O and Al-O speciation are studied. Density maximizes in glasses containing Pb2+ and minimizes in glasses with Al3+. The optical absorption cutoff wavelength increases with the addition of heavy metal ions while Al3+ shifts it to lower wavelengths. W6+, Nb5+ and Al3+ strengthen the borotellurite network and enhance the glass transition temperatures, however Pb2+ decreases it. The glass transition temperature is a linear function of the average single bond energy of the glass network. 11B Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared studies found that the BO4 structural units are unstable in the presence of Al3+, W6+ and Nb5+, however Pb2+ have an opposite effect and promote the formation of BO4. 27Al MAS NMR showed that alumino-borotellurite glasses contain AlO6, AlO5 and AlO4 structural units whose relative concentrations depend on alumina mol. %. Raman spectroscopy was used to determine Te-O coordination in glasses, the later decreased on adding metal ions and Al3+ produced a maximum suppression of TeO4 units.
The structure of WO 3-TeO 2 glasses containing 15, 20 and 25 mol% WO 3 are studied by neutron dif... more The structure of WO 3-TeO 2 glasses containing 15, 20 and 25 mol% WO 3 are studied by neutron diffraction (ND), high energy X-ray diffraction (XRD) and X-ray Absorption Near Edge spectroscopy (XANES). The short-range structural properties of glasses i.e. TeeO and WeO speciation, coordination number distributions, bond-lengths, and the OeTeeO, OeWeO and OeOeO bond angle distributions in the glass network are determined by the Reverse Monte Carlo (RMC) simulations of the ND and XRD data. RMC technique successfully determined all partial pair correlation functions and the coordination number distributions revealed that glass network consists predominantly of TeO 4 and WO 4 units with small amounts of triangular, penta and hexa coordinated units. The average WeO and TeeO bond lengths are in the ranges: 1.69–1.75 ± 0.01 Å and 1.99–2.00 ± 0.01 Å respectively. Both WeO and TeeO correlation peaks are asymmetrical, that indicate a distribution of their bond lengths in the respective structural units. The O-Te-O bond angle distribution has a peak at 107 ± 2°. Similarly the O-W-O bond angle distribution has a peak at 108 ± 5°. On increasing the WO 3 concentration from 15 to 25 mol%, the average TeeO coordination number decreases from 3.80 to 3.61 ± 0.02 due to the structural transformation: TeO 4 → TeO 3 , similarly the WeO coordination also decreases and is in the range: 3.79–3.67 ± 0.02. XANES studies found that the oxidation state of Te and W ions in the glasses are 4 + and 6 + respectively.
A B S T R A C T Glass and anti-glass samples of Bi 2 O 3-TeO 2 and Bi 2 O 3-Nb 2 O 5-TeO 2 were p... more A B S T R A C T Glass and anti-glass samples of Bi 2 O 3-TeO 2 and Bi 2 O 3-Nb 2 O 5-TeO 2 were prepared by ice-water quenching and normal-quenching respectively. The bismuth tellurite system has poor glass forming ability (GFA) and forms a glassy phase at low Bi 2 O 3 concentration of 2 to 5-mol%. On increasing Bi 2 O 3 concentration to 10 mol%, a mixture of glass and anti-glass phases are formed by rapid quenching of the melt. A further increase in Bi 2 O 3 concentration to 20 mol%, produces a sample consisting of entirely Bi 2 Te 4 O 11 anti-glass upon melt-quenching. An anti-glass is a solid, which has long range order of cations (Te 4+ , Bi 3+ , Nb 5+ etc.) but these are statistically distributed at their sites while the anion sites are partially vacant. Consequently the X-ray diffraction (XRD) patterns of bismuth tellurite and bismuth niobium tellurite anti-glass samples show sharp XRD peaks but the Raman spectra show broad phonon bands due to disturbed short-range order of the anions. The addition of Nb 2 O 5 to the Bi 2 O 3-TeO 2 system significantly enhances the GFA. Samples from the system: xBi 2 O 3-xNb 2 O 5-(100-2x)TeO 2 grow micro-inclusions or spherulites of size of several micron within the glass matrix on slow melt-cooling. Heat treatment of 7.5Bi 2 O 3-7.5Nb 2 O 5-85TeO 2 sample show structural transitions from glass→ anti-glass →crystalline phases.
A B S T R A C T BaO-TeO 2 glasses containing 10 to 20-mol% BaO were studied by X-ray diffraction,... more A B S T R A C T BaO-TeO 2 glasses containing 10 to 20-mol% BaO were studied by X-ray diffraction, density, thermal analysis, UV–visible and Raman spectroscopy. The effects of Eu 3 + , Dy 3 + , Er 3 + and Nd 3 + on the density, thermal, optical absorption and luminescent properties of barium tellurite glasses were studied. The short-range structure of barium tellurite glasses consists of TeO 4 trigonal bipyramidal and TeO 3 trigonal pyramidal units. TeeO coordination (N TeeO) was determined by Raman studies; it was found that that N TeeO decreases with increase in BaO and rare earth oxide concentration. The glass transition temperature is a function of both the average single bond enthalpy and non-bridging oxygen concentration in the glass network. Glasses containing Dy 3 + and Eu 3 + show strong visible light photoluminescence, and our results show that barium tellurite glasses are suitable hosts for rare earth ion luminescence due to low phonon energies.
Keywords: V2O5 thin films Thermo-optical effect XRR GIXRD Optical properties Raman spectra a b s ... more Keywords: V2O5 thin films Thermo-optical effect XRR GIXRD Optical properties Raman spectra a b s t r a c t Crystalline V 2 O 5 films of thicknesses in the range: 78–119 nm were prepared on glass sub-strates by thermal evaporation with in-situ substrate heating at 350 • C. XRD studies found the growth of highly oriented orthorhombic V 2 O 5 films with two peaks corresponding to (001) and (002) crystal planes. Raman studies also confirmed the formation of orthorhom-bic V 2 O 5 phase. Electrical studies by two-probe study showed an increase in conductivity with temperature indicating the semiconducting nature of the samples. Optical studies found that UV–vis transmittance is maximum and the reflectance is minimum in film with lowest thickness. The values of activation energy for conduction are 0.15 eV, 0.16 eV and 0.19 eV and those of optical band gap are 2.85 eV, 2.63 eV and 2.67 eV for films of thicknesses: 78 nm, 88 nm and 119 nm respectively. Grazing incidence X-ray reflectivity studies on the film samples showed that the surface roughness increases with increase in thickness and that the density of the samples is 70.6% of that of the bulk V 2 O 5. In-situ high temperature Raman studies up to 60 • C found that the Raman bands at 283 cm −1 and 305 cm −1 broaden considerably and decrease in intensity with increase in temperature; these bands however recover their original shape on cooling. Both peak broadening and recovery effects occur with time lag of ∼30 min and ∼20 min respectively. A decrease in average UV–vis-NIR transmission of ∼1% was observed with increase in temperature, and this thermo-optical effect is reversible.
Tellurite and borotellurite glasses containing Bi 2 O 3 and TiO 2 were prepared and structure-pro... more Tellurite and borotellurite glasses containing Bi 2 O 3 and TiO 2 were prepared and structure-property correlations were carried out by density measurements, X-ray diffraction, Differential Scanning Calorimetry (DSC), Raman, FTIR, UV–visible and 11 B MAS-NMR studies. Titanium-tellurite and titanium bismuth tellurite glasses require high melt-cooling rates and were prepared by splat quenching. On adding B 2 O 3 , the glass forming ability (GFA) enhances considerably and bulk glasses could be synthesized at lower quenching rates. The density of glasses shows a direct correlation with molecular mass of the constituents. UV–visible studies were used to determine the optical band gap and refractive index. Raman studies found that the coordination number of tellurium ions with oxygen (N TeeO) remains constant with variation in TiO 2 molar content, while the incorporation of B 2 O 3 and Bi 2 O 3 decreases N TeeO. DSC studies show that the glass transition temperature (T g) increases with B 2 O 3 and TiO 2 concentrations and that T g correlates well with bond enthalpy of the metal oxides. 11 B MAS-NMR studies found that the coordination number of boron with oxygen (N BeO) decreases with increase in B 2 O 3 content while increasing TiO 2 and Bi 2 O 3 concentration does not significantly modify N BeO .
A B S T R A C T Alumino-tellurite glasses with wide range of Al 2 O 3 concentration (1 to 20-mol%... more A B S T R A C T Alumino-tellurite glasses with wide range of Al 2 O 3 concentration (1 to 20-mol%) are prepared and their short-range structural and thermal properties are studied by Raman spectroscopy, 27 Al Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) and Differential Scanning Calorimetry (DSC). Glass sample with 1-mol% of Al 2 O 3 has TeeO coordination of 3.66, which is close to the value of 3.68 reported in pure TeO 2 glass. TeeO coordination decreases steadily to 3.33 on increasing alumina content to 20-mol%. 27 Al MAS-NMR studies found that Al ions exist in hexa, penta and tetrahedral coordination in the alumino-tellurite network. On increasing alumina content from 3 to 20-mol%, the concentration of hexa-coordinated AleO units decreases from 54% to 35% with a simultaneous increase in the concentration of penta and tetra coordinated AleO units. Glass transition temperature increases with increase in Al 2 O 3 concentration and correlates directly with the average single bond enthalpy of the glass network.
Tellurite and borotellurite glasses containing Bi 2 O 3 and TiO 2 were prepared and structure-pro... more Tellurite and borotellurite glasses containing Bi 2 O 3 and TiO 2 were prepared and structure-property correlations were carried out by density measurements, X-ray diffraction, Differential Scanning Calorimetry (DSC), Raman, FTIR, UV–visible and 11 B MAS-NMR studies. Titanium-tellurite and titanium bismuth tellurite glasses require high melt-cooling rates and were prepared by splat quenching. On adding B 2 O 3 , the glass forming ability (GFA) enhances considerably and bulk glasses could be synthesized at lower quenching rates. The density of glasses shows a direct correlation with molecular mass of the constituents. UV–visible studies were used to determine the optical band gap and refractive index. Raman studies found that the coordination number of tellurium ions with oxygen (N TeeO) remains constant with variation in TiO 2 molar content, while the incorporation of B 2 O 3 and Bi 2 O 3 decreases N TeeO. DSC studies show that the glass transition temperature (T g) increases with B 2 O 3 and TiO 2 concentrations and that T g correlates well with bond enthalpy of the metal oxides. 11 B MAS-NMR studies found that the coordination number of boron with oxygen (N BeO) decreases with increase in B 2 O 3 content while increasing TiO 2 and Bi 2 O 3 concentration does not significantly modify N BeO .
Alumina coatings have been deposited on glass substrates by reactive ac (41 kHz) magnetron sputte... more Alumina coatings have been deposited on glass substrates by reactive ac (41 kHz) magnetron sputtering of two hollow aluminum targets in argon-oxygen plasma at 5 kW sputtering power in the poisoned mode and in the unstable region of hysteresis loop of reactive sputtering. The poisoned mode produces nanocrystalline films of γ and δ alumina at a low deposition rate of 0.06 nm·s-1. Amorphous alumina films have been grown at a higher deposition rate of 0.2 nm·s-1 with the aid of optical emission spectroscopy in which the feedback signal of Al emission spectral line at 396 nm monitored Al concentration in the plasma discharge and accomplished the controlled oxidation of targets during reactive sputtering. Dynamic secondary ion mass spectroscopy studies confirm that alumina films grown in the unstable region of the hysteresis loop of reactive sputtering are highly stoichiometric and of uniform composition with film thickness. Our study demonstrates the successful coupling of optical emission spectroscopy with hollow cylindrical magnetrons for deposition of alumina films.
Bismuth tellurite and bismuth borotellurite samples were synthesized and structure-property corre... more Bismuth tellurite and bismuth borotellurite samples were synthesized and structure-property correlations were carried out by density, X-ray diffraction, dielectric measurements, differential scanning calorimetry, infrared, Raman and 11 B Magic Angle Spinning Nuclear Magnetic Resonance studies. Low concentration of Bi 2 O 3 (5-mol %) forms bismuth tellurite glass while higher concentration of Bi 2 O 3 (10 and 20-mol%) produces anti-glasses on splat-quenching the melt. The short-range structure of bismuth borotellurite glasses consists of TeO 4 , TeO 3 , BO 4 and BO 3 structural units. Raman studies show that TeeO coordination (N TeeO) in bismuth tellurite glass and anti-glass samples decreases from 3.48 to 3.43 with increase in Bi 2 O 3 concentration from 5 to 20-mol%. On incorporating 20-mol% of B 2 O 3 into bismuth tellurite sample, N TeeO decreases to 3.33 and the glass forming ability enhances significantly as compared to that of bismuth tellurite system. On increasing B 2 O 3 upto 40-mol%, the BeO coordination decreases steadily. The addition of Bi 2 O 3 produces the structural transformation: TeO 4 → TeO 3 in Bi 2 O 3-TeO 2 system while B 2 O 3 produces the structural transformation: BO 4 → BO 3 in Bi 2 O 3-B 2 O 3-TeO 2 series without significantly modifying N TeeO. The glass transition temperature increases from 371 °C to 410 °C on increasing B 2 O 3 from 20 to 40-mol%, this increase is due to increase in the concentration of stronger BeO linkages at the expense of weaker TeeO bonds. Decrease in the dielectric constant from 24.1 to 19.3 with B 2 O 3 concentration is due to decrease in density while the polarizability of bismuth borotellurite series remains constant.
A B S T R A C T Alumino-tellurite glasses with wide range of Al 2 O 3 concentration (1 to 20-mol%... more A B S T R A C T Alumino-tellurite glasses with wide range of Al 2 O 3 concentration (1 to 20-mol%) are prepared and their short-range structural and thermal properties are studied by Raman spectroscopy, 27 Al Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) and Differential Scanning Calorimetry (DSC). Glass sample with 1-mol% of Al 2 O 3 has TeeO coordination of 3.66, which is close to the value of 3.68 reported in pure TeO 2 glass. TeeO coordination decreases steadily to 3.33 on increasing alumina content to 20-mol%. 27 Al MAS-NMR studies found that Al ions exist in hexa, penta and tetrahedral coordination in the alumino-tellurite network. On increasing alumina content from 3 to 20-mol%, the concentration of hexa-coordinated AleO units decreases from 54% to 35% with a simultaneous increase in the concentration of penta and tetra coordinated AleO units. Glass transition temperature increases with increase in Al 2 O 3 concentration and correlates directly with the average single bond enthalpy of the glass network.
Laser direct write of silver nanoparticles from solution onto glass substrates for surface-enhanc... more Laser direct write of silver nanoparticles from solution onto glass substrates for surface-enhanced Raman spectroscopy Appl. Phys. Lett. 91, 023107 (2007); 10.1063/1.2753090 Surface enhanced Raman scattering of p-aminothiophenol self-assembled monolayers in sandwich structure fabricated on glass
Thermoelastic and texture behavior of aluminum at high pressure and high temperature investigated... more Thermoelastic and texture behavior of aluminum at high pressure and high temperature investigated by in situ neutron diffraction J. Appl. Phys. 95, 4645 (2004); 10.1063/1.1688460 High‐pressure in situ investigation of cubanite (CuFe2S3): Structural phase transition Abstract. Synchrotron based angle dispersive x−ray diffraction (ADXRD) studies were performed on metastable crystalline bismuth orthoborate (BiBO 3) up to 14.5 GPa during compression and decompression cycle. These studies revealed that the BiBO 3 is unstable and it converts to Bi 4 B 2 O 9 phase at high pressure. Moreover the transformation is found to be irreversible.
Tungsten trioxide (WO 3) thin films were deposited on silica, silicon and alumina substrates and ... more Tungsten trioxide (WO 3) thin films were deposited on silica, silicon and alumina substrates and their crystal structure, surface morphology, optical and gas-sensing properties were compared with those of WO 3 nanoparticles. As-deposited films were amorphous and crystallized into the mon-oclinic phase with heat treatment. Raman spectroscopy revealed that the short-range structure of amorphous, crystalline films and nanoparticles of WO 3 are similar, but the amorphous phase contain W 6+ = O terminal bonds that do not exist in bulk and nanocrystalline samples. Raman studies confirmed that amorphous samples contain higher concentration of hydrogen and hydroxyl ion impurities, which affect the optical bandgap. Thin films show a response of 3 for 150 ppm of H 2 S and 7 for 2000 ppm of C 2 H 5 OH. Platelet shaped nanoparticles exhibit higher response of 37 and fast response and recovery times of 1 to 2 min for 150 ppm of H 2 S.
ABSTRACT Thin films of amorphous alumina were prepared on fused silica substrates by e-beam evapo... more ABSTRACT Thin films of amorphous alumina were prepared on fused silica substrates by e-beam evaporation technique without any deliberate substrate heating. The effects of thermal annealing of alumina films on the structural and optical properties were investigated for annealing temperatures of 600°C, 800°C, 950°C, 1050°C and 1130°C. The present study focuses on investigating the thermal and mechanical stability of the films and phase and structural transformations as a function of heat treatment. With increasing temperature, different crystallographic phases were observed to grow in the films. The most dominant phases were γ and δ alumina which were stable upto 1100°C. Optical properties of the films were measured by UV-visible optical spectroscopy and refractive index value was measured to be 1.66 +/- 0.01 for an amorphous film. The refractive index increased to 1.78 +/- 0.01 (at a wavelength of 700 nm) on crystallization of amorphous coatings.
The mass attenuation coefficient, the effective atomic number and the effective electron density ... more The mass attenuation coefficient, the effective atomic number and the effective electron density are basic quantities for determining the penetration of gamma-ray photons in matter. Tabulations of mass attenuation coefficients and interaction cross sections have been published eg, ...
Tungsten trioxide (WO 3) thin films were deposited on silica, silicon and alumina substrates and ... more Tungsten trioxide (WO 3) thin films were deposited on silica, silicon and alumina substrates and their crystal structure, surface morphology, optical and gas-sensing properties were compared with those of WO 3 nanoparticles. As deposited films were amorphous and crystallized into the mon-oclinic phase with heat treatment. Raman spectroscopy revealed that the short-range structure of amorphous, crystalline films and nanoparticles of WO 3 are similar, but the amorphous phase contain W 6+ = O terminal bonds that do not exist in bulk and nanocrystalline samples. Raman studies confirmed that amorphous samples contain higher concentration of hydrogen and hydroxyl ion impurities, which affect the optical bandgap. Thin films show a response of 3 for 150 ppm of H 2 S and 7 for 2000 ppm of C 2 H 5 OH. Platelet shaped nanoparticles exhibit higher response of 37 and fast response and recovery times of 1 to 2 min for 150 ppm of H 2 S.
The effects of addition of Al3+, W6+, Nb5+ and Pb2+ on the density, thermal, optical properties o... more The effects of addition of Al3+, W6+, Nb5+ and Pb2+ on the density, thermal, optical properties of borotellurite glasses and on the B-O, Te-O and Al-O speciation are studied. Density maximizes in glasses containing Pb2+ and minimizes in glasses with Al3+. The optical absorption cutoff wavelength increases with the addition of heavy metal ions while Al3+ shifts it to lower wavelengths. W6+, Nb5+ and Al3+ strengthen the borotellurite network and enhance the glass transition temperatures, however Pb2+ decreases it. The glass transition temperature is a linear function of the average single bond energy of the glass network. 11B Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared studies found that the BO4 structural units are unstable in the presence of Al3+, W6+ and Nb5+, however Pb2+ have an opposite effect and promote the formation of BO4. 27Al MAS NMR showed that alumino-borotellurite glasses contain AlO6, AlO5 and AlO4 structural units whose relative concentrations depend on alumina mol. %. Raman spectroscopy was used to determine Te-O coordination in glasses, the later decreased on adding metal ions and Al3+ produced a maximum suppression of TeO4 units.
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