Comparative study of the effect of the incorporation of cobalt and nickel oxides on the density and optical properties of copper tellurite glasses

Two series of ternary semiconducting glasses with composition 65 TeO₂-(35–x)CuO-xMO in mole percent (x=0, 0.5, 1, 2, 3, 4 and M stands for Co or Ni) were prepared by a melt quenching technique. The densities of annealed and unannealed disc-shaped samples and the optical energy gap of thin blown films of both series of glasses were measured, and the comparative effect of each transition metal (TM) oxide was estimated. It was found that forx=0.5 to 1 mol% andx=2 to 4mol%, the optical energy gap (E _opt) was somewhat greater in TeO₂-CuO-NiO than in TeO₂-CuO-CoO glasses. This increase inE _opt is interpreted in terms of the decreasing number of non-bridging oxygen ions with the increase of each TM oxide. NiO was found to be more effective in increasing the density than CoO in annealed copper tellurite glasses.     

Different effects of nickel and cobalt additions on the electronic conduction of copper tellurite glasses

Measurements of the d.c. electrical conductivity were made on 65TeO₂-(35-x)CuO-x(MO) (mol %) glasses wherex=0, 0.5, 1, 2, 3, 4 and M represents nickel or cobalt. A variation in the conductivity and activation energy of the glasses is observed as CuO is replaced by NiO and by CoO. It is found that withx=0.5 to 3 mol % of NiO, the conductivity increases and the activation energy decreases due to the decrease in effective electron hopping distance between the transition metal (TM) ions. The conductivity is found to decrease with the substitution of 4 mol % of NiO and 0.5 to 4 mol % of CoO and this is attributed to the decrease in relative concentration of hopping centres because of the decrease in the hopping transitions between ions of the same element (e.g. Cu⁺ and Cu²⁺ ions) and between the ions of different TM elements (e.g. Cu⁺ and Ni²⁺, Cu⁺ and Co²⁺). This decrease in conductivity has also been described due to the formation of Ni-O-Ni, Cu-O-Ni and Co-O-Co, Cu-O-Co bridge bonds in NiO-and CoO-doped glasses respectively. The CoO-doped glasses have been found to be of a more insulating nature.     

Phase separation in tellurite glass-forming systems containing B2O3,GeO2,Fe2O3,MnO,CoO,NiO and CdO

The boundaries between the regions of single-phase and two-phase glasses were established in tellurite glass-forming systems containing B₂O₃ and one of the following oxides: GeO₂, Fe₂O₃,CoO, NiO, MnO and CdO. The character of the microstructures inside and outside the regions of stable phase separation were determined by electron microscopy. It was shown that the existing microheterogeneities may either result from incomplete liquid immiscibility during melting and supercooling or be due to typical metastable separation.     

Thermal and optical properties of tellurite glasses doped erbium

Er³⁺-doped tellurite glasses with molar compositions of 75TeO₂–20ZnO–(5 − x) Na₂O–xEr₂O₃ (x = 0, 0.5, 1, 2, 3, and 4 mol%) have been elaborated from the melt-quenching method. The effects of Er₂O₃ concentration on the thermal stability and optical properties of tellurite glasses have been discussed. From the differential scanning calorimetry (DSC) profile, the glass transition temperature T _g, and crystallization onset temperature T _x are estimated. The thermal stability factor, defined as ∆T = T _x − T _g, was higher than 100 °C. It suggests that tellurite glass exhibits a good thermal stability and consequently is suitable to be a potential candidate for fiber drawing. Furthermore, the stability factor increases with Er₂O₃ concentration up to 2 mol% then presents a continue decrease suggesting of beginning of crystallization of highly doped tellurite glasses. The refractive index and extinction coefficient data were obtained by analyzing the experimental spectra of tanΨ and cos∆ measured by spectroscopic ellipsometry (SE). The complex dielectric functions (ε = ε₁ + iε₂) of the samples were estimated from regression analysis. The fundamental absorption edge has been identified from the optical absorption spectra and was analyzed in terms of the theory proposed by Davis and Mott. The values of optical band gap for direct and indirect allowed transitions have been determined. An important decrease of the optical band gap was found after Er doping. It was assigned to structural changes induced from the formation of non-bridging oxygen. The absorption coefficient just below the absorption edge varies exponentially with photon energy indicating the presence of Urbach’s tail. The origin of the Urbach energy is associated with the phonon-assisted indirect transitions.     

Electron spin resonance in copper phosphate and copper tellurite glasses containing strontium

Two series of ternary copper phosphate and copper tellurite glasses containing strontium were prepared and the electron spin resonance spectra of glasses of compositions 65 (P₂O₅)-(35-x) CuO-xSrO and 65 (TeO₂)-(35-x) CuO-xSrO where x varied from 0–10 mol % were investigated. From the results and the chemical analyses of the samples it was found that a reduction in the copper (II) signal intensity in the glass samples as the proportion of alkaline earth metal is raised, corresponds to an increase in the reduced valency ratio, C, in the glasses.     

Structural,physical, and optical characterization of (Nd3+/Eu3+)-doped zinc-rich silica–borate glasses

In this study, zinc–silica–borate glass structures doped with rare earth (RE) oxides Eu₂O₃ and Nd₂O₃ were synthesized with classical melting–quenching technique. 60ZnO–10SiO₂–(30 – x)B₂O₃:xRE (x?=?0, 0.5, 1, 1.5 mol%) composition was chosen as the structure. The doping effect of two different rare earth oxides (individually) at different ratios was investigated according to the structural, physical, and optical properties of the glass structure. Structural properties of the synthesized glasses were determined with Fourier transform infrared (FTIR) device, and densities (ρ) and molar volumes (V_m) of the glasses were measured with Archimedes method, and optical properties were determined with UV–Visible (UV–Vis-NIR) device. FTIR results show that BO₃ units increased in all RE-doped glasses. While densities of the synthesized glasses varied between 3.755 and 3.941 g cm^??3, indirect bandgaps varied between 3.219 and 3.645 eV. The glass with the highest transmittance was the 1% Eu₂O₃-doped glass with a transmittance of 84%. While band edges shifted slightly toward short wavelengths in glasses doped with Nd₂O₃, they shifted to longer wavelengths in glasses doped with Eu₂O₃.

     

Novel Tm-doped fluorotellurite glasses with enhanced quantum efficiency

In this paper, new highly Tm³⁺-doped tellurite glasses with host composition 75TeO₂-xZnF₂-yGeO₂-12PbO-3Nb₂O₅ [x(5-15), y(0-5) mol%] are presented and compared to the Tm-doped tellurite glasses based on the traditional host composition: 75TeO₂-20ZnO-5Na₂O mol%. Enhanced quantum efficiency from ³F₄ level was observed for the proposed glasses and thermal stability and viscosity values make them suitable for optical fiber drawing. Besides the host composition, substantial influence of Tm³⁺ concentration on luminescence and lifetime of excited ³F₄ and ³H₄ states were discussed.     

Chemical approach to the conduction mechanism in copper tellurite glasses containing lutetium oxide

Measurements of d.c. electrical conductivity were made on 65TeO₂-(35 -x)CuO-xLu₂O₃ (mol%) glasses with x=0, 1, 2, 3, 4. The experimental results show that whenx is changed from 1 to 2 mol%, the conductivity increases due to the additional electrons obtained by the oxidation of TeO₂ as well as due to the Cu⁺ Cu²⁺ transition under the effect of interelectronic repulsion in the 4f shell of the lutetium present in the glass. Whenx is increased to greater than 2 mol%, the conductivity decreases because hopping is inhibited due to the formation of oxygen bridge associates or because of the strong ligand repulsive field of lutetium indicating its non-reactivity in the glassy network. The conductivity has a distinct maximum atx=2.     

ESR and optical absorption spectra of Ni(II) ions in lithium fluoroborate glasses

The results of the investigation of the structure of Ni(II) ions in x LiF-(100–x) B₂O₃ glasses with 5x30 mol% using ESR and optical absorption techniques are reported. Electron spin resonance spectra of Ni(II) ions doped glasses exhibit a symmetric line shape centred at g=2.36±0.01 at room temperature. Remarkable changes have been observed in the intensity and line shape with changes in concentration of LiF and when the spectra were recorded in the temperature range 123–453 K. The optical absorption spectra were recorded at room temperature. The observed bands have been interpreted in terms of ligand field theory. From the spectral analysis, the crystal field parameter, Dq, and the Racah interelectronic repulsion parameters, B and C, have been evaluated. By correlating the ESR and optical absorption data, the covalency parameter has been evaluated.     

Physical and optical properties of Co2+, Ni2+ doped 20ZnO + xLi2O + (30 − x)K2O + 50B2O3 (5 ≤ x ≤ 25) glasses: Observation of mixed alkali effect

Co²⁺ and Ni²⁺ ions doped 20ZnO + xLi₂O + (30 ? x) K₂O + 50B₂O₃ (5 ≤ x ≤ 25) mol% glasses are prepared using melt quenching technique. Structural changes of the prepared glasses by addition of transition metal oxides, CoO and NiO are investigated by UV–vis–NIR, FT-IR spectroscopy and XRD. The XRD pattern indicates the amorphous nature of prepared glasses. FT-IR measurements of the all glasses revealed that the network structure of the glasses are mainly based on BO₃ and BO₄ units placed in different structural groups in which the BO₃ units being dominant. The optical absorption spectra suggest the site symmetry of Co²⁺ and Ni²⁺ ions in the glasses are near octahedral. Crystal field and inter-electronic repulsion parameters are also evaluated. The optical band gap and Urbach energies exhibited the mixed alkali effect. Various physical parameters such as density, refractive index, optical dielectric constant, polaron radius, electronic polarizability and inter-ionic distance are also determined.     

Refractive index patterning of tellurite glass surfaces by ultra short pulse laser spot heating

Dot patterns of refractive indices were formed by the laser pulse irradiation on the tellurite glasses. The ternary tellurite glasses of TeO₂-Na₂O-Al₂O₃, TeO₂-Na₂O-GeO₂ and TeO₂-Na₂O-TiO₂ doped with 2 mol% of CoO were irradiated by a femtosecond pulse laser beam (800 nm) or by a green light beam (532 nm) from a second harmonic generator of a Q switch pulse YAG laser. The refractive index map of the glass was composed with an He-Ne laser beam by an scanning ellipsometric technique at a resolution of 100 m × 50 m, indicating that the spots possessing refractive index lower by about 0.05–0.38 than the surroundings were formed at the region irradiated by the laser beam. The irradiation of the femtosecond laser beam generated the dot patterns roughly equivalent to the beam size. The change of refractive index could be tunable by adjusting laser power, suggesting that the process could be applied to optical recording.     

FT-IR,Raman and UV–VIS spectroscopic studies of copper doped 3Bi<Subscript>2</Subscript>O<Subscript>3 </Subscript>·B<Subscript>2</Subscript>O<Subscript>3</Subscript> glass matix

FT-IR, Raman and UV–VIS experimental results were presented for xCuO·(100-x)[3Bi₂O₃·B₂O₃] glass system, where 0 ≤ x ≤ 50 mol%. The FT-IR measurements indicate the presence in xCuO·(100-x)[3Bi₂O₃·B₂O₃] glasses of BO₃, BO₄ units, BiO₃ pyramidal and distorted BiO₆ octahedral units and their dependence of CuO content. The Raman scattering data indicate that for 0 ≤ x ≤ 10 mol% the structure of studied glasses consist from BiO₃ pyramidal and distorted BiO₆ octahedral units, ring and chain type of metaborate groups, ortoborate and pyroborate groups. For higher concentration the Raman spectra suggest that the structure become more disordered. The FT-IR and Raman bands characteristic for CuO were not directly evidenced, but the absorption bands specific for the glass matrix are influenced by the presence of copper ions in the glass network structure. The optical absorption confirms the presence of Cu²⁺ in the CuO doped 3Bi₂O₃·B₂O₃ glass matrix.     

Devitrification and vitrification of tellurite glasses

The crystallization of pure tellurite glass during various heating rates was studied. The activation energy for crystallization was 115 × 10²² eV mol^–1. The glass transformation, T _g, starting crystallization, T _x, crystallization, T _c and melting temperatures, T _m, have been reported for binary tellurite glasses of the form (1 – x) TeO₂–xA_nO_m [A_nO_m = MnO₂, Co₃O₄ and MoO₃]. Among many different parameters of the glass forming potential the two-thirds rule, T _g/T _m, the glass stabilization range, T= T _x – T _g, and the glass forming tendency, K _g= (T _c– T _g)/(T _m – T _c), are reported for the first time for tellurite glasses.     

Composition and concentration dependence of spectroscopic properties of Nd-doped tellurite and metaborate glasses

The spectroscopic properties of tellurite glasses of composition (in mol%) TNKNd: (70 − x)TeO₂-15Nb₂O₅-15K₂O-xNd₂O₃ (x = 0.1, 1.0, 1.5, 2.0 and 2.5) and TNLNd10: 69TeO₂-15Nb₂O₅-15Li₂O-1.0Nd₂O₃ and lithium metaborate glass of composition LBNNd10: 89LiBO₂-10Nb₂O₅-1.0Nd₂O₃ have been investigated using absorption and emission spectra and decay curve analysis. An energy level analysis has been carried out considering the experimental energy positions of the absorption and emission bands, using the free-ion Hamiltonian model. The spectral intensities have been calculated by using the Judd-Ofelt theory and in turn the radiative properties such as radiative transition probabilities, emission cross-sections, branching ratios and radiative lifetimes have been estimated. The decay curves at the lower concentrations are exponential while they show a non-exponential behavior at higher concentrations (?1.0 mol%) due to energy transfer processes. The effective lifetimes for the ⁴F_3/2 level are found to decrease with increase in Nd₂O₃ concentration for all the glasses under investigation. The non-exponential decay curves have been well-fitted to the Yokota-Tanimoto model with S = 6, indicating that the nature of energy transfer is of dipole-dipole type and energy migration also plays an important role. The results obtained have been compared with Nd³⁺-doped phosphate, fluorophosphate, lead borate, tellurite, germanate and silicate glasses and Nd³⁺-doped YAG ceramic and Ca₂Nb₂O₇ crystals.     

A Universal Strategy for Hollow Metal Oxide Nanoparticles Encapsulated into B/N Co‐Doped Graphitic Nanotubes as High‐Performance Lithium‐Ion Battery Anodes

Yolk–shell nanostructures have received great attention for boosting the performance of lithium‐ion batteries because of their obvious advantages in solving the problems associated with large volume change, low conductivity, and short diffusion path for Li⁺ ion transport. A universal strategy for making hollow transition metal oxide (TMO) nanoparticles (NPs) encapsulated into B, N co‐doped graphitic nanotubes (TMO@BNG (TMO = CoO, Ni₂O₃, Mn₃O₄) through combining pyrolysis with an oxidation method is reported herein. The as‐made TMO@BNG exhibits the TMO‐dependent lithium‐ion storage ability, in which CoO@BNG nanotubes exhibit highest lithium‐ion storage capacity of 1554 mA h g^?1 at the current density of 96 mA g^?1, good rate ability (410 mA h g^?1 at 1.75 A g^?1), and high stability (almost 96% storage capacity retention after 480 cycles). The present work highlights the importance of introducing hollow TMO NPs with thin wall into BNG with large surface area for boosting LIBs in the terms of storage capacity, rate capability, and cycling stability.     

Manifestation of Nd ions on the structure,Raman and IR spectra of (TeO<Subscript>2</Subscript>-MoO-Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>) glasses

The structure of [80TeO₂ + (20–x)MoO + xNd₂O₃] glasses, with x = 0, 4, 6, 10 and 12 mol%, is studied in this work. Raman scattering in the spectral range (−2000 to 3500 cm⁻¹) and IR absorption spectra have been measured for crystalline TeO₂ and glasses, and their assignments were discussed and compared. Many vibrational modes were found active in both Raman and IR and their assignments for crystalline TeO₂ and for the glasses were discussed in relation to the tetragonal structure of crystalline α -TeO₂. Nd₂O₃ was found to completely eliminate diffuse scattering and enhance the Raman scattering intensity. Anti-stokes Raman bands in the range −1460 cm^{− 1} to −1975 cm^{− 1} were observed for both (30Li₂O + 70B₂O₃+ xNd₂O₃) glasses and [80TeO₂ + (20−x)MoO + xNd₂O₃] glasses and were attributed to some emission processes due to the doping of the glasses with Nd₂O₃.     

Structure of cobalt and fluorine doped hexaferrites

Hexagonal ferrites in the BaO-Fe₂O₃- CoO system have the M, Y, Z, W and S structures. BaFe_12–x CO _x O_19–x prepared by the glass synthesis method crystallizes with the M structure but forx > O a few CoFe₂O₄ (S) crystallizes at first and then is located at the core of the recovered platelets of hexaferrite M. BaFe₁₆– _x CO_{2 +x} O_27-x F _x prepared in the saure way has not the W structure but is a mixture of cobalt doped M and S.     

Thermal-lens study of thermo-optical properties of tellurite glasses

Mode-mismatched Thermal Lens (TL) measurements were performed in 70TeO₂–19WO₃–7Na₂O–4Nb₂O₅ (% mol) tellurite glasses doped with either Er³⁺ or Tm³⁺ and co-doped with Er³⁺/Tm³⁺ ions. Thermo-optical parameters (D, K, ds/dQ and ds/dT) were obtained in function of thulium concentrations (0.39–1.6) × 10 ²⁰ ions/cm³. For Er³⁺/Tm³⁺ co-doped tellurite glasses, D and K values are practically independent of the Tm³⁺ concentrations used in this study. The average values of D and ds/dT obtained for tellurite glasses are: (3.1 ± 0.2) × 10⁻³ cm²/s and (16 ± 3) × 10⁻⁶ K⁻¹, respectively.     

Influence of modifier oxides on some physical properties of antimony borate glass system doped with V2O5

Three series of glasses, of the composition 20 MO (M = Ca, Pb, Zn)–40 Sb₂O₃–(40 − x) B₂O₃:xV₂O₅, with six values of x ranging from 0 to 1 mol% were prepared. The samples were characterized by X-ray diffraction, scanning electron microscopy, EDS and differential scanning calorimetric techniques. The comparison of DSC data among the three series has indicated high glass forming ability for ZnO mixed glasses. Dielectric properties over a range of frequency and temperature, optical absorption, ESR spectra at room temperature and IR spectra have been investigated. The variations observed in all these properties due to different modifiers as a function of the concentration of V₂O₅ have been analyzed in the light of different oxidation states and environment of vanadyl ions in these glasses. The analysis of these results indicated that the ZnO mixed glasses are more stable against devetrification and possess high insulating strength when compared with PbO and CaO mixed glasses.     

Non-linear concentration-dependent electrical properties of some semiconducting vanadate glasses

Characterizations of (50 – x) P₂O₅-x M-50V₂O₅ (M = Bi₂O₃, Sb₂O₃, and GeO₂ and x=0 to 45 mol% M) and P₂O₅-Bi₂O₃ semiconducting oxide glasses have been made from studies of electrical conductivities (both a.c. and d.c.) in the temperature range 77 to 400 K. All these glasses showed some interesting non-linear variation of d.c. and a.c. conductivity, together with other properties for particular values of M (between 20 and 30 mol% M). Because the non-vanadate (1–x) P₂O₅-x Bi₂O₃ glasses also showed similar conductivity anomaly (minimum) around 25 mol% Bi₂O₃ with a corresponding maximum in the activation energy (W), it is concluded (in contradiction to earlier suggestions) that not only the ratio (= V⁵⁺/V⁴⁺) but also the network-former ions in the vanadate glasses make a substantial contribution to the anomalous concentration variation of the physical properties of these glasses. The electrical conduction in these glasses is found to be mainly due to hopping of polarons in the adiabatic approximation. At low temperature, the d.c. conductivity obeys Mott's T ^–1/4 behaviour. The a.c. conductivity obeying the general ^s law (exponent s lying between 0.85 and 0.98) supports the theory based on the hopping over the barrier model.