Electronic Polarizability Of Oxide Ion Research Articles

Structural and optical properties of TeO2- SeO2-Na2O glass system

80 TeO2-(20-x) SeO2-xNa2O (where x = 0, 5, 10, 15, 20 mol %) ternary glass system have been successfully prepared by conventional melt-quenching method. The non-crystalline nature of the tested glass samples has been confirmed by X-ray diffraction. The structural transformation in the tested glass samples has been evaluated by measuring density (ρ), molar volume (VM), oxygen packing density (OPD) and oxygen molar volume (V0) values. The characteristic temperature of the glass system (glass transition,Tg, crystallization, Tc ) decreases with increasing Na2O content. Raman spectra show that addition of Na2O to TeO2 + SeO2 glass may result in cleavage of Te-O-Te and Se-O-Se linkages and formation of TeO3- and SeO3- terminal groups in the glass system. FTIR spectra show that the units of TeO4 units decrease and the units of TeO3 / TeO3+1 increase in the tested glass samples. The cut-off wavelength (λC), optical band gap (Eopt), refractive index (n), molar refraction (RM), metallization criterion (M), molar polarizability (αm), electronic polarizability of oxide ion (αo2-), optical basicity (Λ), Fermi energy (EF), dispersion energy (Ed), single oscillator energy (E0) and Urbach energy (ΔE) have been calculated from optical absorption spectra. The reflectivity of light and extinction coefficient (k) is used to find imaginary part of dielectric constant (εi). The optical band gap energy and allowed transitions have been investigated using five methods; indirect, direct, indirect forbidden, direct forbidden and imaginary part of the dielectric constant. The optical band gap values of direct transition are in well agreement with the optical band values of an imaginary part of dielectric constant. The obtained optical band gap values decrease with increasing sodium oxide in the glass samples. Increase in Urbach energy values in the present glass system is due to an increase in the number of defects in the glass structure. The tested glass samples possess higher values of Urbach energy, molar electronic polarizability, and optical basicity. The excitation energy E0 decreases with the increase of Na2O content in the glass system.

The influence of oxides on the optical properties of tellurite glasses

New tellurite glasses within composition 75TeO2–5WO3–15Nb2O5–5MxOy in mol%, where MxOy = (Na2O, Ag2O, ZnO, MgO, CuO, NiO, TiO2, MnO2), have been prepared using the conventional melt-quenching method. The optical properties of these glasses were estimated by measuring the ultraviolet–visible–near infrared (UV–vis–NIR) spectroscopy and linear refractive indices at different wavelengths. From the absorption edge studies, the values of the optical band gap (Eopt) and Urbach energy (ΔE) were evaluated. The density, molar volumes, molar refraction (Rm), molar polarizability (), metallization criterion (Mc), electronic polarizability of oxide ions (), and optical basicity (Λ) were estimated. Moreover, the nonlinear refractive index (n2), third-order nonlinear susceptibility (χ(3)), and nonlinear absorption coefficient (β) were observed. It was found that the linear and nonlinear refractive indexes increase with decreasing the optical energy gap.

MIXED ALKALI EFFECT IN (40-x)K2O–xLi2O-10Na2O–50B2O3 GLASSES—PHYSICAL AND OPTICAL ABSORPTION STUDIES

So far only a handful of publications have been concerned with the study of the mixed alkali effect in borate glasses containing three types of alkali ions. In the present work, the mixed alkali effect (MAE) has been investigated in the glass system (40–x) K2O–x Li2O –10Na2O–50B2O3. (0≤x≤40 mol%) through density and modulated DSC studies. The density and glass transition temperature of the present glasses varies non-linearly exhibiting mixed alkali effect. We report the mixed alkali effect in the present glasses through optical properties. From the absorption edge studies, the various values of optical band gap (Eo) and Urbach energy (ΔE) have been evaluated. The values of Eo and ΔE show non-linear behavior with compositional parameter showing the mixed alkali effect. The band gap energy based average electronic polarizability of oxide ions αO2–(Eo) , optical basicity A(Eo) , and Yamashita–Kurosawa’s interaction parameter A(Eo) have been examined to check the correlations among them and bonding character. Based on good correlation among electronic polarizability of oxide ions, optical basicity and interaction parameter, the present K2O– Li2O–Na2O–B2O3 glasses are classified as normal ionic (basic) oxides.

Mixed alkali tungsten borate glasses – Optical and structural properties

Glasses with composition xLi2O-(30-x)Na2O-10WO3-60B2O3 (where x=0, 5, 10, 15, 20, 25, and 30mol%) were prepared by the melt quenching technique. Density, refractive index and glass transition temperature varies non-linearly with glass composition indicting the presence of mixed alkali effect. Optical energy band gap for various indirect and direct (allowed and forbidden) transitions were determined using Tauc plots. IR spectral study reveals the existence of BO3 and BO4 groups with W–O–W vibrations in the present glasses. Based on good correlation among refractive index based electronic polarizability of oxide ions, optical basicity and the Yamashita–Kurosawa’s interaction parameter, the present Li2O–Na2O–WO3–B2O3 glasses were classified as semi covalent oxides.

Temperature dependence of refractive index and electronic polarizability of RO–TeO2 glasses (R=Mg, Ba, Zn)

The refractive indices (n) and densities (ρ) of xRO − (100 − x)TeO2 glasses (R = Mg, Ba, and Zn) with x = 10–40 are measured in the temperature range of 50–150 °C in order to clarify thermo-optic coefficients (dn/dT) and the temperature dependence of the electronic polarizability of oxide ions (αO2−) and optical basicity (Λ). It is found that the values of n, αO2−, and Λ increase almost linearly with increasing temperature. The values of dn/dT are between 7.32 and 9.69 × 10−5 K−1 and tend to decrease with increasing RO content. Contrary, the values of ⅆαO2−/ⅆT and dΛ/dT are almost constant irrespective of RO content. It is suggested that the electronic polarizability has an important contribution on thermo-optic coefficients, but the contribution of volume thermal expansion on thermo-optic coefficients is not ignored. In the analyses of electronic polarizabilities of RO–TeO2 glasses, the concept of group optical basicity for TeO3 and TeO4 structural units is also applied. It is explained that large thermo-optic coefficients in RO–TeO2 glasses are composed of oxides having small average single bond strengths and large optical basicities.

Mixed alkali effect in physical and optical properties of Li2O–Na2O–WO3–B2O3 glasses

Glasses with composition xLi2O-(30−x)Na2O–10WO3–60B2O3 (where x=0, 5, 10, 15, 20, 25 and 30mol%) have been prepared using the melt quenching technique. In the present work, the mixed alkali effect (MAE) has been investigated in the above glass system through density and modulated DSC studies. The density and glass transition temperature of the present gasses varies non-linearly, the exhibiting the mixed alkali effect. From the optical absorption studies, the values of direct optical band gap, indirect optical band gap energy (Eo) and Urbach energy(ΔE) have been evaluated. The values of Eo and ΔE vary non-linearly with composition parameter, showing the mixed alkali effect. The electronic polarizability of oxide ions, optical basicity and the Yamashita–Kurosawa's interaction parameter have been examined to check the correlation among them and bond character. Based on good correlation among electronic polarizability of oxide ions, optical basicity and the Yamashita–Kurosawa's interaction parameter, the present Li2O–Na2O–WO3–B2O3 glasses were classified as normal ionic (basic) oxides.

Influence of SiO 2 on dispersive conductivity and absorption edge of calcium bismuthate glasses

The dynamics of Ca 2+ ions and the optical properties of calcium bismuth silicate glasses were investigated using relaxation spectroscopy and optical absorption spectra. These glasses were prepared by normal melt quench technique. Density, molar volume and glass transition temperature (T g) have been measured. A large difference in the values of T g and crystalline temperature (T C) suggests the thermal stability of these glasses. The ac and dc conductivities, activation energy for dc conduction (E dc) and for relaxation frequency (E τ) were extracted from the impedance spectra. The compositional variation in conductivity has been attributed to the presence of mixed glass former effect in these glasses. Both electric modulus and the conductivity formalism have been employed to study the relaxation dynamics of charge carriers in these glasses. A single ‘master curve’ for normalized plots of all the modulus isotherms observed for a given composition indicates that the dynamic processes for ions in these glasses are temperature independent. Similar values of E dc and E τ indicate that the ions have to overcome the energy barrier of same height in their conduction as well as relaxation. The observed conductivity spectra follows power law with exponent ‘s’ which increases regularly with frequency and approaches unity at higher frequencies. It has been observed that the position of the absorption edge and cutoff wavelength shift towards blue as Bi 2O 3/SiO 2 ratio decreases. The compositional variation in optical band gap (E g) has been attributed to the influence of the CaO and SiO 2 on conduction band. The values of Urbach energy confirm the existence of phonon-assisted indirect transitions in the present glass system. The average electronic polarizability of oxide ion (α O 2−) and the optical basicity (Λ th) have been estimated from the calculated values of the optical band gap and were found to be dependent directly on Bi 2O 3/SiO 2 ratio.

Physical and optical studies in mixed alkali borate glasses with three types of alkali ions

So far only a handful of publications have been concerned with the study of the mixed alkali effect in borate glasses containing three types of alkali ions. In the present work, the mixed alkali effect (MAE) has been investigated in the glass system (40− x)Li 2O– xNa 2O–10K 2O–50B 2O 3. (0 ≤ x ≤ 40 mol%) through density and modulated DSC studies. The density and glass transition temperature of the present glasses varies non-linearly exhibiting mixed alkali effect. The glass stability is observed to be less which may be important for the present glasses as promising material for non-optical applications. We report, for the first time, the mixed alkali effect in the present glasses through optical properties. From the absorption edge studies, the values of indirect optical band gap ( E opt), direct optical band gap and Urbach energy (Δ E) have been evaluated. The values of E opt and Δ E show non-linear behavior with compositional parameter showing the mixed alkali effect. The average electronic polarizability of oxide ions α O 2 − , optical basicity Λ, and Yamashita–Kurosawa's interaction parameter A have been examined to check the correlations among them and bonding character. Based on good correlation among electronic polarizability of oxide ions, optical basicity and interaction parameter, the present Li 2O–Na 2O–K 2O–B 2O 3 glasses are classified as normal ionic (basic) oxides.

Approach to thermal properties and electronic polarizability from average single bond strength in ZnOBi 2O 3B 2O 3 glasses

The glass transition temperature ( T g), density, refractive index, Raman scattering spectra, and X-ray photoelectron spectra (XPS) for xZnO– yBi 2O 3– zB 2O 3 glasses ( x=10–65, y=10–50, z=25–60 mol%) are measured to clarify the bonding and structure features of the glasses with large amounts of ZnO. The average electronic polarizability of oxide ions ( α O2−) and optical basicity ( Λ) of the glasses estimated using Lorentz–Lorenz equation increase with increasing ZnO or Bi 2O 3 content, giving the values of α O2−=1.963 Å 3 and Λ=0.819 for 60ZnO–10Bi 2O 3–30B 2O 3 glass. The formation of BOBi and BOZn bridging bonds in the glass structure is suggested from Raman and XPS spectra. The average single bond strength ( B MO ) proposed by Dimitrov and Komatsu is applied to the glasses and is calculated using single bond strengths of 150.6 kJ/mol for ZnO bonds in ZnO 4 groups, 102.5 kJ/mol for BiO bonds in BiO 6 groups, 498 kJ/mol for BO bonds in BO 3 groups, and 373 kJ/mol for BO bonds in BO 4 groups. Good correlations are observed between T g and B MO , Λ and B MO , and T g and Λ, proposing that the average single bond strength is a good parameter for understanding thermal and optical properties of ZnOBi 2O 3B 2O 3 glasses.

Electronic polarizability and its temperature dependence of Bi 2O 3–B 2O 3 glasses

The refractive index ( n) and density ( ρ) of xBi 2O 3–(100 − x)B 2O 3 glasses with x = 32.5–60 (mol%) are measured in the temperature range of 30–150 °C in order to clarify the temperature dependence of the electronic polarizability of oxide ions ( α O2− ) and optical basicity ( Λ). It is found that the values of n, α O2− , and Λ increase almost linearly with increasing temperature. The value of the temperature dependence of refractive index, d n/d T, increases with increasing Bi 2O 3 content. Contrary, the values of d α O2 − /d T, and d Λ/d T, tend to decrease with increasing Bi 2O 3 content. It is suggested that the temperature dependence of the electronic polarizability of oxide ions in xBi 2O 3–(100 − x)B 2O 3 glasses has a large contribution for the temperature dependence of the refractive index in comparison with the contribution of the volume thermal expansion coefficient. The features in the temperature dependence of α O2− and Λ in the present glass system might be related to the extremely weak single bond strength of Bi 2O 3 compared with the strong single bond strength of B 2O 3.

Thermo‐Optic Properties and Electronic Polarizability in Alkali Tellurite Glasses

The refractive indices (n) and densities (ρ) of xLi2O–(100−x)TeO2 glasses with x=15–30 and xNa2O–(100−x)TeO2 glasses with x=10–20 are measured in the temperature range of 30°–150°C in order to clarify thermo‐optic coefficients (dn/dT) and the temperature dependence of the electronic polarizability of oxide ions ( ) and optical basicity (Λ). It is found that the values of n, , and Λ increase almost linearly with increasing temperature. The values of dn/dT are around 7 × 10−5 K−1 and tend to decrease with increasing alkali content (Li2O, Na2O). In contrast, the values of d/dT and dΛ/dT are almost constant, irrespective of the alkali content. It is suggested that electronic polarizability has an important contribution on thermo‐optic coefficients, but the contribution of volume thermal expansion on thermo‐optic coefficients cannot be ignored. In the analyses of electronic polarizabilities of alkali tellurite glasses, the concept of group optical basicity for TeO3 and TeO4 structural units is also applied. It is explained that large thermo‐optic coefficients in Li2O–TeO2 and Na2O–TeO2 glasses are composed of oxides having small average single bond strengths and large optical basicities.

Influence of SiO 2 on the structure and optical properties of lithium bismuth silicate glasses

Bismuth silicate glasses containing lithium oxide with composition 20Li 2O·(80 − x)Bi 2O 3· xSiO 2 (5 ⩽ x ⩽ 70 mol%) have been prepared by melt-quench technique. Density ( D), molar volume ( V M) and glass transition temperature ( T g) for all the glass samples have been measured. FTIR spectroscopy has been employed to investigate the structure of these glasses in order to obtain information about the competitive role of Bi 2O 3 and SiO 2 in the formation of glass network. The increase of SiO 2 content in the glass matrix results in increasing the Si–O–Si bond angle and hence the ionicity of Si–O bond increases with decrease in Bi 2O 3/SiO 2 ratio. The optical transmittance spectra of all the glasses have been recorded in the wavelength range 200–3300 nm. The values of optical band gap ( E g) have been determined from the cutoff wavelength of these glasses. The average electronic polarizability of oxide ion ( α o 2 - ) and the optical basicity ( Λ th) have been estimated from the calculated values of the E g and were found to be dependent directly on Bi 2O 3/SiO 2 ratio. The variation in different physical parameters such as D, V M and T g and optical parameters; viz., E g, α o 2 - , Λ th with Bi 2O 3/SiO 2 ratio have been analyzed and discussed in terms of change in the glass structure.

Temperature dependence of refractive index and electronic polarizability of KNbGeO5 glass and its nanocrystallized glasses

The refractive indices (n) and densities (ρ) of a glass and transparent nanocrystallized glasses with the composition of 25K2O-25Nb2O5–50GeO2 (i.e., KNbGeO5) are measured in the temperature range of 30–150 °C in order to clarify the temperature dependences of the electronic polarizability of oxide ions (αO2−) and optical basicity (Λ). It is found that the values of n, αO2−, and Λ increase almost linearly with increasing temperature, and the values of the temperature dependence of these properties, i.e., dn/dT, dαO2−/dT, and dΛ/dT, tend to decrease slightly due to the nanocrystallization. It is clarified that the temperature dependence of the electronic polarizability of oxide ions in the precursor glass and nanocrystallized glasses has a large contribution for the temperature dependence of the refractive index in comparison with the contribution of density (volume thermal expansion). The features in the temperature dependences of αO2− and Λ in the present glass system is related to the large optical basicities of the constituent oxides of K2O, Nb2O5, and GeO2.

Electronic polarizability and optical basicity of lanthanide oxides

The average electronic polarizability of oxide ions α O 2 - in p- and s-block, d transition metal and heavy s- and p-block oxides has been calculated by Duffy and Dimitrov. However, lanthanide oxides have not yet been well revealed, which are promising materials for luminescence and nonlinear optical. In this study, new data of the average electronic oxide polarizability of rare earth oxides have been calculated on the basis of linear refractive index n 0 and energy gap E g. The optical basicity Λ of rare earth oxides has been estimated on the basis of average electronic oxide polarizability calculated from the refractive index n 0 and the energy gap E g. Our present conclusion suggests that lanthanide oxide should be supplemented to the second group according to the values of their oxide polarizability. We also looked for another lanthanide contraction phenomenon that the electronic polarizability of oxide ion decreases with increasing atomic number. Furthermore, close correlations are investigated among α O 2 - , Λ, E g , and n 0 in this paper.