Electron paramagnetic resonance, optical and electrical properties of vanadyl doped alkali germanoborate glasses

Glasses with composition xGeO₂.(0.30−x)M₂O.0.70B₂O₃ (M=Li, K) containing 2.0 mol% of V₂O₅ have been prepared in the range 0.00≤x≤0.15 by normal melt quenching method. Electron paramagnetic resonance (EPR), optical transmission and absorption spectra and dc conductivity of these glasses have been studied. Spin Hamiltonian parameters (SHPs) of VO²⁺ ions, dipolar hyperfine coupling parameter, P, Fermi contact interaction parameter, K and molecular orbital coefficients (α² and γ²) have been calculated. In GeO₂·Li₂O·B₂O₃ glasses there is no change in the tetragonality of the V⁴⁺O₆ complex and the size of 3d_xy orbit also remains unchanged with increase in GeO₂ content. In GeO₂·K₂O·B₂O₃ glasses, there is an increase in the tetragonality of the V⁴⁺O₆ complex and the 3d_xy orbit expands with increase in GeO₂ content. Values of the theoretical optical basicity, Λ_th, have also been reported. Optical band gap decreases with increase in GeO₂ content. The dc conductivity of these glasses decreases and the activation energy increases with increase in GeO₂:M₂O ratio.     

Structural investigation of xAg2O·(100−x)·[2B2O3·As2O3] glasses doped with manganese ions

Structural analysis of x[(100−y)Ag₂O·yMnO]·(100−x)[2B₂O₃·As₂O₃] glasses, with x=10 mol% and 0≤y≤10 mol%, was performed by means of FT-IR and FT-Raman spectroscopies. The purpose of this work is to investigate the structural changes that appear in the xAg₂O·(100−x)·[2B₂O₃·As₂O₃] glasses with the addition and increase in manganese ions content. FT-IR measurements revealed the presence of pyro-, ortho-, di-, tri-, tetra- and penta-borate groups and structural units characteristic to As₂O₃ in the structure of the studied glasses. FT-IR spectroscopy measurements also show that BO₃ units are the main structural units of the glass system. The presence of structural units characteristic to Ag₂O were not directly evidenced by FT-IR spectroscopy. In addtition, the FT-Raman analysis evidenced the presence of boroxol rings in the structure of the studied glasses.     

Effect of WO3 on EPR, structure and electrical conductivity of vanadyl doped WO3·M2O·B2O3 (M=Li, Na) glasses

Glasses with composition xWO₃·(30−x)M₂O·70B₂O₃ (M=Li, Na; 0≤x≤15) doped with 2 mol% V₂O₅ have been prepared using the melt-quench technique. The electron paramagnetic resonance spectra have been recorded in X-band (ν≈9.14 GHz) at room temperature (RT). The spin Hamiltonian parameters, dipolar hyperfine coupling parameter and Fermi contact interaction parameter have been calculated. It is observed that the resultant resonance spectra contain hyperfine structures (hfs) only due to V⁴⁺ ions, which exist as VO²⁺ ions in octahedral coordination with a tetragonal compression in the present glass system. The tetragonality increases with WO₃:M₂O ratio and also there is an expansion of 3d_xy orbit of unpaired electron in the vanadium ion. The study of IR transmission spectra over a range 400-4000 cm⁻¹ depicts the presence of WO₆ group. The DC conductivity (σ) has been measured in the temperature range 423-623 K and is found to be predominantly ionic.     

Synthesis and laser patterning of Bi-doped Y3Fe5O12 crystals in germanosilicate glasses

New germanosilicate glasses giving the crystallization of yttrium iron garnet Y₃Fe₅O₁₂ (YIG) and Bi-doped YIG, 23Na₂O-xBi₂O₃-(12−x)Y₂O₃-25Fe₂O₃-20SiO₂-20GeO₂ (mol%), are developed, and the laser-induced crystallization technique is applied to the glasses to pattern YIG and Bi-doped YIG crystals on the glass surface. It is clarified from the Mössbauer effect measurements that iron ions in the glasses are present mainly as Fe³⁺. It is suggested from the X-ray diffraction analyses and magnetization measurements that Si⁴⁺ ions are incorporated into YIG crystals formed in the crystallization of glasses. The irradiations (laser power: 32-60 mW and laser scanning speed: 7 μm/s) of continuous wave Yb:YVO₄ fiber laser (wavelength: 1080 nm) are found to induce YIG and Bi-doped YIG crystals, indicating that Fe³⁺ ions in the glasses act as suitable transition metal ions for the laser-induced crystallization. It is suggested that YIG and Bi-doped YIG crystals in the laser irradiated part might orient. The present study will be a first step for the patterning of magnetic crystals containing iron ions in glasses.     

Effect of ZnO/CdO on the structure and electrical conductivity in Li2O·MO·Bi2O3·B2O3 glasses (M=Zn, Cd)

Studies of structural and electrical properties have been carried out on a number of glasses with wide ranging compositions in the glass systems Li₂O·MO·Bi₂O₃·B₂O₃ (where M=Zn or Cd), in order to understand the effect of transition metal (TM) ions on the structure of these glasses. The density and molar volume measurements have also been made to understand the structural changes occurring in these glasses. The dc conductivity measured in the temperature range 423-623 K obeys Arrhenius law. It increases with increase in Li₂O/MO ratio. The results of infrared spectra indicate that TM ions (Zn²⁺ or Cd²⁺) behave as network former in the present system. Boron exists in both tri- and tetra-hedral units in these glasses and no boroxol ring formation takes place in the glass structure. Values of theoretical optical basicity have also been reported.     

Second-harmonic generation in the thermal/electrical poling (100−x)GeS2·x(0.5Ga2S3·0.5CdS) chalcogenide glasses

Utilizing Maker fringe (MF) method, second-harmonic generation (SHG) has been observed within the GeS₂-Ga₂S₃-CdS pseudo-ternary glasses through thermal/electrical poling technique. The SHG phenomenon was considered to be the result of breakage of the glassy macroscopic isotropy originated from the reorientations of dipoles during the thermal/electrical poling process. Under the same poling condition conducted with 5 kV and 280 °C for 30 min, the maximum value of second-order nonlinear susceptibility χ⁽²⁾ of the poled (100−x)GeS₂·x(0.5Ga₂S₃·0.5CdS) glasses was obtained to be ≈4.36 pm/V when the value of x is equal to 30. Nonlinear dependence of χ⁽²⁾ on compositions of these glasses can be well explained according to the theory related to the reorientation of dipoles.     

Crystallization kinetics of Li2O-PbO-V2O5 glasses

Lead vanadate glasses of the system 5Li₂O−(45−x) PbO−(50+x) V₂O₅, with x=0, 5, 10, and 15 mol% have been prepared and studied by differential scanning calorimetry (DSC). The crystallization kinetics of the glasses were investigated under non-isothermal conditions applying the formal theory of transformations for heterogeneous nucleation to the experimental data obtained by DSC using continuous-heating techniques. In addition, from dependence of the glass-transition temperature (T_g) on the heating rate, the activation energy for the glass transition was derived. Similarly the activation energy of the crystallization process was determined and the crystallization mechanism was characterized. The results reveal the increase of the activation energy for glass transition which was attributed to the increase in the rigidity, the cross-link density and the packing density of these glasses. The phases into which the glass crystallizes have been identified by X-ray diffraction. Diffractograms of the transformed material indicate the presence of microcrystallites of Li_0.30V₂O₅, Li_0.67O₅V₂, LiV₆O₁₅, Li₄O₄Pb, and O₇Pb₂V₂ in a remaining amorphous matrix.     

Conversion of covalent to ionic character of V2O5–CeO2–PbO–B2O3 glasses for solid state ionic devices

xV₂O₅–xCeO₂–(30−x)PbO–(70−x) B₂O₃ glasses are synthesized by using the melt quench technique. The number of studies such as XRD, density, molar volume, optical band gap, refractive index and FTIR spectroscopy are employed to characterize the glasses. The band gap decreases from 2.20 to 1.78 eV and density increases from 3.49 to 4.25 g/cm³. FTIR spectroscopy reveals that incorporation of V₂O₅ in glass network helps to convert the structural units of [BO₃] into [BO₄]. At higher concentration of vanadium, VO vibration of [VO₅] structural units and V–O–V vibration are present. The bond ionicity of glasses increases with incorporation of V₂O₅ contents.     

Dielectric dispersion in PbO-Sb2O3-As2O3:V2O5 glasses

Dielectric properties, viz. dielectric constant ε′, loss tan δ and a.c conductivity σ_ac (over a wide range of frequency and temperature) and dielectric breakdown strength of PbO-Sb₂O₃-As₂O₃ glasses doped with V₂O₅ (ranging from 0 to 0.5 mol%) are studied. Analysis of these results, based on optical absorption and ESR spectra, indicates that the insulating strength of the glasses is comparatively high when the concentration of V₂O₅ is about 0.3 mol% in the glass matrix.     

Antiferromagnetic phase transition in garnet-type AgCa2Co2V3O12 and AgCa2Ni2V3O12

Antiferromagnetic phase transition in two vanadium garnets AgCa₂Co₂V₃O₁₂ and AgCa₂Ni₂V₃O₁₂ has been found and investigated extensively. The heat capacity exhibits sharp peak due to the antiferromagnetic order with the Néel temperature T_N=6.39 K for AgCa₂Co₂V₃O₁₂ and 7.21 K for AgCa₂Ni₂V₃O₁₂, respectively. The magnetic susceptibilities exhibit broad maximum, and these T_N correspond to the inflection points of the magnetic susceptibility χ a little lower than T(χ_max). The magnetic entropy changes from zero to 20 K per mol Co²⁺ and Ni²⁺ ions are 5.31 J K⁻¹ mol-Co²⁺-ion⁻¹ and 6.85 J K⁻¹ mol-Ni²⁺-ion⁻¹, indicating S=1/2 for Co²⁺ ion and S=1 for Ni²⁺ ion. The magnetic susceptibility of AgCa₂Ni₂V₃O₁₂ shows the Curie-Weiss behavior between 20 and 350 K with the effective magnetic moment μ_eff=3.23 μ_B Ni²⁺-ion⁻¹ and the Weiss constant θ=−16.4 K (antiferromagnetic sign). Nevertheless, the simple Curie-Weiss law cannot be applicable for AgCa₂Co₂V₃O₁₂. The complex temperature dependence of magnetic susceptibility has been interpreted within the framework of Tanabe-Sugano energy diagram, which is analyzed on the basis of crystalline electric field. The ground state is the spin doublet state ²E(t₂⁶e) and the first excited state is spin quartet state ⁴T₁(t₂⁵e²) which locates extremely close to the ground state. The low spin state S=1/2 for Co²⁺ ion is verified experimentally at least below 20 K which is in agreement with the result of the heat capacity.     

Investigation of spectroscopic properties and thermal stability of Er/Yb-co-doped Bi2O3-B2O3-Ga2O3 glasses

A series of Er³⁺/Yb³⁺-co-doped 60Bi₂O₃-(40−x) B₂O₃ -xGa₂O₃ (BBGA x=0, 4, 8, 12, 16 mol%) glasses have been prepared. The absorption spectra, emission spectra, fluorescence lifetime of Er³⁺:⁴I_13/2 level and thermal stability were measured and investigated. Three Judd-Ofelt intensity parameters Ω_t (t=2,4,6) (Ω₂=(4.67-5.93)×10⁻²⁰ cm², Ω₄=(1.50-1.81)×10⁻²⁰ cm², Ω₆=(0.92-1.17)×10⁻²⁰ cm²) of Er³⁺ ions were calculated by Judd-Ofelt theory. It is found that the Ω₆ first increases with the increase of Ga₂O₃ content from 0 to 8 mol% and then decreases, which is mainly affected by the number of non-bridging oxygen ions of the glass network. The high peak of stimulated emission cross-section () of Er³⁺: ⁴I_13/2→⁴I_15/2 transition were obtained according to McCumber theory and broad full width at half maximum (FWHM=69-76 nm) of the ⁴I_13/2→⁴I_15/2 transition of Er³⁺ ions were measured. The results indicate that these new BBGA glasses can be used as a candidate host material for potential broadband optical amplifiers.     

Thermoluminescence of B2O3-Li2O glass system doped with MgO

Lithium borate (LiB) glasses in the system (100−x)B₂O₃-xLi₂O with x=20, 30, 40, 50, 60 and 70 mol% were prepared. The glasses were doped with different concentrations of the order of 10⁻¹, 10⁻², 10⁻³, 10⁻⁴ and 10⁻⁵ of MgO and their thermoluminescent (TL) response was investigated. The irradiations were performed using γ rays from a ⁶⁰Co source in the dose range from 0.1 to 25 kGy. The material displayed good sensitivity for γ-rays and intensity of TL signals is dependent on γ-ray dose and Li₂O content. For each dose level and investigated temperature range (50-350 °C), exactly single isolated glow peak appears in the temperature range of 165-205 °C depending on both Li₂O concentrations and time of exposure. The shape of the glow peak has altered significantly with increase in the gamma ray dose or Li₂O concentrations. The glass composition with x=50 mol% doped with 10⁻³ mol% of MgO presented the best TL response. The results of the present study indicated that the recorded single and isolated high temperature peak is a good candidate for TL dosimetric investigations. This indicates that 50 B₂O₃-50Li₂O-doped with 10⁻³ mol% of MgO is possibly used as materials for radiation dosimetry in the dose range of 0.1-20 kGy.     

Influence of valence states and co-ordination of cobalt ions on dielectric properties of PbO-Bi2O3-As2O3:CoO glass system

The glasses of the composition (40−x) PbO-15Bi₂O₃-45As₂O₃-xCoO, with 0≤x≤0.6 mol% in the steps of 0.1 were synthesized. The dielectric properties viz., dielectric constant, loss and ac conductivity over moderately larger ranges of frequency and temperature were investigated. The results were analyzed with the aid of the data on optical absorption and IR spectra. The analysis indicated that there is an increase in the insulating strength of the glasses with increase in the concentration of CoO up to 0.4 mol%.     

Optical properties of samarium doped zinc-phosphate glasses

Samarium doped zinc-phosphate glasses having composition Sm₂O_{3 (x)}ZnO_(60−x) P₂O_{5 (40)} (where x=0.1-0.5 mol%) were prepared by melt quenching method. The density of these glasses was measured by Archimedes method; the corresponding molar volumes have also been calculated. The values of density range from 3.34 to 3.87 gm/cm³ and those of molar volume range from 27.62 to 31.80 cm⁻³. The optical absorbance studies were carried out on these glasses to measure their energy band gaps. The absorption spectra of these glasses were recorded in UV-visible region. No sharp edges were found in the optical spectra, which verifies the amorphous nature of these glasses. The optical band gap energies for these glasses were found to be in the range of 2.89-4.20 eV. The refractive index and polarizability of oxide ion have been calculated by using Lorentz-Lorentz relations. The values of refractive index range from 2.13 to 2.42 and those of polarizability of oxide ion range from 6.51×10⁻²⁴ to 7.80×10⁻²⁴ cm³.     

The influence of microscopic parameters on the ionic conductivity of SrBi2(Nb1−xVx)2O9−δ(0≤x≤0.3) ceramics

Layered SrBi₂(Nb_1−xV_x)₂O_9−δ (SBVN) ceramics with x lying in the range 0-0.3 (30 mol%) were fabricated by the conventional sintering technique. The microstructural studies confirmed the truncating effect of V₂O₅ on the abnormal platy growth of SBN grains. The electrical conductivity studies were centred in the 573-823 K as the Curie temperature lies in this range. The concentration of mobile charge carriers (n), the diffusion constant (D₀) and the mean free path (a) were calculated by using Rice and Roth formalism. The conductivity parameters such as ion-hopping rate (ω_p) and the charge carrier concentration (K′) term have been calculated using Almond and West formalism. The aforementioned microscopic parameters were found to be V₂O₅ content dependent on SrBi₂(Nb_1−xV_x)₂O_9−δ ceramics.     

Low-temperature thermoelectric properties of Bi85Sb15−xNbx alloys prepared by high-press sintering

The nanocrystalline materials with the general formula Bi₈₅Sb_15−xNb_x (x=0, 0.5, 1, 2, 3) were prepared by mechanical alloying and subsequent high-pressure sintering. Their transport properties involving electrical conductivity, Seebeck coefficient and thermal conductivity have been investigated in the temperature range of 80-300 K. The absolute value of Seebeck coefficient of Bi₈₅Sb₁₃Nb₂ reaches a maximum of 161 μV/K at 105 K, which is 69% larger than that of Bi₈₅Sb₁₅ at the same temperature. The power factor and figure-of-merit are 4.45×10⁻³ WK⁻²m⁻¹ at 220 K and 1.79×10⁻³ K⁻¹ at 196 K, respectively. These results suggest that thermoelectric properties of Bi₈₅Sb₁₅ based material can be improved by Nb doping.     

Study of molybdenum coordination state and crystallization behavior in MoO3-La2O3-B2O3 glasses by Raman spectroscopy

The ternary MoO₃-La₂O₃-B₂O₃ glasses containing a large amount of MoO₃ (10-50 mol%) are prepared, and their structure and crystallization behavior are examined from the Raman scattering spectrum measurements and X-ray diffraction analyses. It is found that the glass transition and crystallization temperatures and the thermal stability against crystallization decrease with increasing MoO₃ content. It is suggested that the main coordination state of Mo⁶⁺ ions in the glasses is isolated (MoO₄)²⁻ tetrahedral units giving strong Raman bands at 830-860 and 930 cm⁻¹. It is found that the crystalline phases in the crystallized glasses are mainly LaMoBO₆ and LaB₃O₆, and the main crystallization mechanism in MoO₃-La₂O₃-B₂O₃ glasses is surface crystallization. LaMoBO₆ crystals are found to give strong Raman bands at 810-830 and ∼910 cm⁻¹.     

Writing of two-dimensional crystal curved lines at the surface of Sm2O3-Bi2O3-B2O3 glass by samarium atom heat processing

Two-dimensional crystal curved lines consisting of the nonlinear optical Sm_xBi_1−xBO₃ phase are fabricated at the surface of 8Sm₂O₃·37Bi₂O₃·55B₂O₃ glass by continuous wave Nd:YAG laser (wavelength: 1064 nm) irradiation (samarium atom heat processing) with a power of ∼0.9 W and a laser scanning speed of 5 μm/s. The curved lines with bending angles of 0-90° or with sine-shapes are written by just changing the laser scanning direction. The polarized micro-Raman scattering spectra for the line after bending are the same as those for the line before bending, indicating that the crystal plane of Sm_xBi_1−xBO₃ crystals to the crystal growth direction might be maintained even after the change in the laser scanning direction. It is found from laser scanning microscope observations that the crystal lines at the surface are swelled out smoothly, giving a height of about 10 μm.     

Nickel ion—A structural probe in BaO-Al2O3-P2O5 glass system by means of dielectric, spectroscopic and magnetic studies

BaO-Al₂O₃-P₂O₅ glasses containing different concentrations of NiO (ranging from 0 to 1.0 mol%) were prepared. A number of studies viz., chemical durability, differential thermal analysis, spectroscopic (infrared, optical absorption spectra), magnetic susceptibility and dielectric properties (constant ε′, loss tan δ, AC conductivity σ_AC over a range of frequency and temperature) of these glasses have been carried out. The studies on chemical durability indicate that there is a significant increase in the corrosion resistance of the glasses; where as the results of differential thermal analysis suggests that there is a substantial improvement in the glass forming ability, with increase in the concentration of NiO up to 0.6 mol% in the glass matrix. The optical absorption, magnetic susceptibility and IR spectral studies point out nickel ions occupy both tetrahedral and octahedral positions in the glass network; the later positions seems to be dominant when the concentration of NiO is beyond 0.6 mol% in the glass matrix. The studies of dielectric properties reveal that the presence of nickel oxide in the glass network causes a considerable improvement in the insulating strength of the se glasses when the concentration of NiO?0.6 mol%.     

Influence of B2O3 to the inhomogeneous broadening and spectroscopic properties of Er/Yb codoped fluorophosphate glasses

In a three-components fluorophosphate glass system, the introduction of H₃BO₃ brings some valuable influence to the spectroscopic and thermal properties of the glasses. With H₃BO₃ increases from 2 to 20 mol%, Ω₆, S_ed4I13/2, FWHM, T_g and fluorescence lifetime change from 3.21×10⁻²⁰ cm², 1.77×10⁻²⁰ cm², 45 nm, 480 °C and 8.8 ms to 4.66×10⁻²⁰ cm², 2.11×10⁻²⁰ cm², 50 nm, 541 °C and 7.4 ms, respectively. σ_abs, σ_emi, FWHM×τ_f×σ_emi has a maximum when H₃BO₃ is 11 mol%. T_g and T_x−T_g increases with H₃BO₃ introduction. Results showed that in fluorophosphate glasses, proper amount of B₂O₃ can be used as a modifier to suppress upconversion and improve spectroscopic properties, broadband property and crystallization stability of the glasses while keeps the fluorescence lifetime relatively high.