Structure and magnetic susceptibility of irradiated sodium borate glasses containing nickel oxide

The effect of introducing soda to boric oxide on the optical absorption infrared spectra and magnetic susceptibility of sodium borate glass system containing nickel oxide was studied. It was found that increasing of Na₂O helps in forming the BO₄ group and nonbridging oxygen and the nickel ions change from the octahedral state to the tetrahedral state. The magnetic susceptibility also increases rapidly with gradual increase of soda content up to 20 mol%, and then slightly increases, this may be due to the change in the coordination number of nickel ions. Also the effect of the addition of nickel oxide was studied, it was found that the values of magnetic susceptibility increases with the gradual increase of the nickel oxide, which is due to the increase of Ni²⁺ in octahedral coordination.     

Some physical properties of alkali borate tungstate glasses containing iron

A series of borotungstate glasses was prepared. The glass formation was confirmed by using X-ray diffraction measurements on the powder samples then measured using Mo¨ssbauer, differential thermal analysis (DTA), infra-red (IR) and d.c. conductivity. The iron in the alkali borate tungstate glass was found in the ferric state only. The introduction of tungsten to replace 25 mol % sodium tetraborate in the glass samples caused a little shift in the IR bands toward the lower frequency. The iron ions may act as a glass modifier whereas the tungsten ions may act as network former. The electrical conduction increased in the presence of tungsten due to the hopping mechanism between the two sites of tungsten (W⁵⁺, W⁶⁺).     

Spectroscopic and electrical studies of sodium tetraborate glasses containing nickel oxide

The infrared spectra. X-ray diffraction and electrical conductivity of sodium tetraborate glasses containing nickel have been studied as a function of nickel oxide content. It was found that addition of nickel oxide does not seem to introduce any new absorption band as compared with the infrared spectrum of pure sodium tetraborate glass. The electrical conductivity measurements revealed that the activation energy for conductivity increases with nickel oxide content. This could be explained on the basis of the concept of Hubbard bands, and possibly by a block effect of the nickel ion on the overall mobility of the sodium ion. Measurements were made on unannealed samples and some samples annealed at different temperatures. Annealing the samples at temperatures in the range 460 to 480° C causes the appearance of a crystalline phase, resulting in an increase of electronic conductivity.     

Ultrasonic study and physical properties of some borate glasses

The structure of the glass system (75−x)B₂O₃–xBi₂O₃–25Li₂O, where x=5, 10, 15, and 20 mol% was investigated by using pulse-echo technique. Elastic properties of the glass system have been calculated together with Poisson’s ratio and Debye temperature from the measured densities as well as longitudinal and shear ultrasonic velocities at room temperature. Ultrasonic velocity measurements were taken at 4 MHz. Estimated parameters based on Makishima–Mackenzie theory and bond compression model were calculated in order to analyse the experimental elastic moduli. Addition effect of Bi₂O₃ on the elastic moduli was investigated in terms of the number of network bonds and the mean cross-link density of the glass systems. The average atomic ring size of the network was also calculated and it was found that it depends on the concentration of the modifiers. Composition dependence of the elastic moduli and Poisson’s ratio from one hand and the trend of both the ring diameter and the packing density from the other hand showed structural change at x=15 mol%.     

Structural and thermal properties of some zinc borate glasses containing gadolinium ions

Glasses in the system (Gd₂O₃)_x·(B₂O₃)_(60−x)·(ZnO)₄₀ (0 ≤ × ≤ 15 mol%) have been prepared by the melt-quenching technique. The local structure and the thermal behaviour of the obtained glasses were investigated using X-ray diffraction (XRD), differential thermal analysis (DTA) and Fourier transform infrared (FTIR) spectroscopy. The XRD pattern of the glasses confirmed their amorphous nature. Compositional dependence of the glass transition (T_g), fragility index (F), activation energy of the glass transition (E_g), activation energy for the crystallization process (E_p) were determined by DTA investigations. FTIR data revealed that the short-range order of glasses is affected by the addition of the Gd₂O₃ to the host glass matrix. The compositional dependence of the different structural units which appear in the investigated glasses was followed. FTIR data suggest that the gadolinium ions play the network modifier role in the studied glasses.     

Structural and magnetic properties of strontium–borate glasses containing iron ions

Glasses of the xFe₂O₃·(100 − x)[B₂O₃·SrO] system, with 0 ≤ x ≤ 30 mol%, were studied by EPR and magnetic susceptibility measurements. EPR spectroscopy and magnetic susceptibility measurements show that the Fe³⁺ ions are localized in sites of distorted octahedral symmetry and in clustered formations containing both Fe³⁺ and Fe²⁺ ions. Dipolar and superexchange interactions involving iron ions were revealed depending on the iron content of the sample.     

Ultrasonic velocity in sodium borate glasses

Ultrasonic velocities in sodium borate glasses are measured as a function of composition at a frequency of 10 MHz and at a temperature of 298 K by making use of the ultrasonic pulse echo overlap method. Elastic properties of these glasses are analysed in terms of the elastic internal energy due to deformation; elastic resistances of the network-former, B₂O₃, and the modifier, Na₂O, are obtained as a function of composition from the plot ofMV ² againstx ₂, whereM is the molar mass of sodium borate glasses,V the velocity of sound andx ₂ the mole fraction of Na₂O. The elastic resistances of B₂O₃ and Na₂O are as follows: (i) forx ₂<0.33, the elastic resistance of B₂O₃ is smaller than that of Na₂O; (ii) atx ₂=0.33, the elastic resistances of B₂O₃ and Na₂O are equal; (iii) forx ₂>0.33, the elastic resistance of B₂O₃ is greater than that of Na₂O; (iv) atx ₂≈0.15, the elastic resistances of B₂O₃ and Na₂O become respectively maximal and minimal; (v) atx ₂≈0.23, the elastic resistances of B₂O₃ and Na₂O become respectively minimal and maximal; (vi) abovex ₂=0.36, the elastic resistance of Na₂O becomes negative.     

Spectroscopic investigations and physical properties of Mn doped mixed alkali zinc borate glasses

Spectroscopic investigations on Mn²⁺ doped 20ZnO + xLi₂O + (30−x)Na₂O + 50B₂O₃ (5 ≤ x ≤ 25) (ZLNB) glasses reveal the non-linear behavior in their physical and structural properties. FT-IR spectra of ZLNB glasses reveal diborate units in the borate network. EPR spectra exhibit characteristic resonance signals of Mn²⁺ ions. A well resolved six line hyperfine structure around g = 2.02 corresponds to the sites of Type II, and a weak broad shoulder around g = 2.7 followed by an unresolved intense signal at g = 4.25 corresponding to sites of Type I are observed for their respective transitions. A large value of zero-field splitting parameter (D) is observed and it behaves non-linearly, reaches a maximum at x = 15 mol% with increase in Li₂O content. Δg values reveal the ionic nature of glass systems. Optical absorption spectra suggest the distorted octahedral site symmetry of Mn²⁺ ions in the host. Mixed alkali effect is evident in bandgap and Urbach energies.     

Ultrasonic studies on irradiated sodium borate glasses

The ultrasonic velocity and attenuation coefficient have been measured at the frequency 4 MHz and at room temperature using the pulse echo technique. The effect of γ-radiation (1–10 Gy) on the ultrasonic attenuation, the internal friction and elastic properties inside the modified sodium borate glasses was studied. The used modification oxides are CaO, ZnO, MgO, BaO, and CdO. The results indicate the possibility for using modified sodium borate glasses as γ-ray dosimeters in the low γ-radiation doses.     

Microwave properties of vanadium borate glasses

A.c. conductivity, dielectric constant and loss, and variation with temperature (302–373 K) for four different compositions of V₂O₅-B₂O₃ glasses were reported at 9.586 GHz microwave frequency. The quality factor (Q) and attenuation factor (α being the important parameters in the microwave range of applications were also studied. The change in the dielectric constant and loss was observed with composition of V₂O₅. The maximum loss was found to be at 15V₂O₅ mol‰ The peak was observed in loss with temperature.     

Spectroscopic properties of the Ce-doped borate glasses

The EPR, optical absorption and photoluminescence (emission and excitation) spectra as well as decay kinetics of a series of the Ce-doped glasses with Li₂B₄O₇, LiKB₄O₇, CaB₄O₇, and LiCaBO₃ compositions have been investigated and analysed. The borate glasses were obtained from the corresponding polycrystalline compounds in the air atmosphere, using standard glass technology. The EPR signals of the isolated Ce³⁺ and pair Ce³⁺–Ce³⁺ centres, coupled by magnetic dipolar and exchange interactions were registered at liquid helium temperatures. The characteristic for glass host broad bands corresponding to the 4f → 5d transitions of the Ce³⁺centres have been observed in the optical absorption and photoluminescence (emission and excitation) spectra. The obtained luminescence decay curves can be satisfactory described by exponential function with lifetimes in the 19.8–26.1 ns range, which depend on the basic glass composition. The local structure of Ce³⁺ centres in the investigated glasses has been considered and discussed.     

The optical properties of some borate glasses

The optical properties of potassium borate and sodium borate glasses are presented. The fundamental absorption edge for all the series of glasses were analysed in terms of the theory of Davis and Mott. The position of absorption edge and hence the value of the optical gap, was found to depend on the semiconducting glass composition, and the absorption in these glasses is believed to be associated with indirect transitions. The infrared spectra were recorded and appeared individually similar, which is consistent with the absence of significant structural change between the various glass specimens.     

Magnetic and electrical properties of lithium borosilicate glasses containing nickel and iron oxides

Measurements of a.c. conductivity, dielectric constants, Mo¨ssbauer spectra and magnetic susceptibility were carried out on samples of composition: 20LiO₂, 31B₂O₅, 34SiO₂, 15 – x NiO, xFe₂O₃ where x = 2.5, 5, 7.5, 10 and 12.5 mol %. It was found that when x is changed from 2.5 to 10 mol % NiO, the conductivity decreases due to the increase of the bridging oxygen ions. When x is increased to greater than 10 mol % NiO, the conductivity increases because of the decrease of the ratio of Fe²⁺Fe³⁺ ions as confirmed from Mo¨ssbauer data. The conductivity has a distinct minimum at 10 mol % NiO. Distribution of relaxation processes was also studied, and two processes were adequate to describe the present experimental data.     

Optical properties of oxide glasses containing transition metals: Case of titanium- and chromium-containing glasses

One of the major driving forces for the development of new glasses is the demand for high optical non-linearity with reduced cost and a higher damage resistance. Oxide glasses with large non-linear refractive index and non-linear absorption coefficient are promising materials for fiber telecommunication and for non-linear optical devices such as ultrafast optical switches, power limiters, real time holography, self-focusing, white-light continuum generation and photonic applications. To get insight into the optical absorption in amorphous materials, studies are still needed for revealing the nature of photoelectronic excitations in these materials by comparison with that in crystals which have been understood firmly based on band theory. Although the IR absorption loss in oxide glasses is larger than of fluorides, low light scattering loss is expected in these oxide glasses because they have lower glass transition temperature. In addition, small concentration of dopant such as alkaline metal and alkaline earth metal elements gives rise to the structural relaxation of the frozen-in density fluctuations even below glass transition temperature T_g, adding to the reduction of T_g as well. A review of the fundamentals and recent research advances in optical properties of oxide glasses containing chromium or titanium is presented.     

Reaction of sodium calcium borate glasses to form hydroxyapatite

This study investigated the transformation of two sodium calcium borate glasses to hydroxyapatite (HA). The chemical reaction was between either 1CaO · 2Na₂O · 6B₂O₃ or 2CaO · 2Na₂O · 6B₂O₃ glass and a 0.25 M phosphate (K₂HPO₄) solution at 37, 75 and 200 °C. Glass samples in the form of irregular particles (125–180 μm) and microspheres (45–90 and 125–180 μm) were used in order to understand the reaction mechanism. The effect of glass composition (calcium content) on the weight loss rate and reaction temperature on crystal size, crystallinity and grain shape of the reaction products were studied. Carbonated HA was made by dissolving an appropriate amount of carbonate (K₂CO₃) in the 0.25 M phosphate solution. X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy were used to characterize the reaction products. The results show that sodium calcium borate glasses can be transformed to HA by reacting with a phosphate solution. It is essentially a process of dissolution of glass and precipitation of HA. The transformation begins from an amorphous state to calcium-deficient HA without changing the size and shape of the original glass sample. Glass with a lower calcium content (1CaO · 2Na₂O · 6B₂O₃), or reacted at an elevated temperature (75 °C), has a higher reaction rate. The HA crystal size increases and grain shape changes from spheroidal to cylindrical as temperature increases from 37 to 200 °C. Increase in carbonate concentration can also decrease the crystal size and yield a more needle-like grain shape.