A spectroscopic study of some sodium tetraborate glasses containing lead and copper

Optical absorption, infra-red absorption spectra and differential scanning calorimetry of amorphous (Na₂B₄O₇)₈₀-(Pb₃O₄)_20-x -(CuO) _x systems were studied as functions of copper content up to 10 mol%. When the Pb₃O₄ in the glasses is gradually replaced by CuO, a pronounced decrease in the optical energy gap and an increase in the optical absorption at 750 nm due to the CU²⁺ ions is observed. The change in the optical absorption may be attributed to the concentration variation of the Cu²⁺ ions in the glasses as a consequence of changing the lead content.     

FTIR spectroscopic study of some bismuth germanate glasses containing gadolinium ions

Since infrared spectroscopy and density are advantageous tools for the investigations of glasses, we have used them to obtain information concerning the local structure of xGd₂O₃·(100 − x)[4Bi₂O₃·GeO₂] glass system, with 0 ≤ x ≤ 30 mol%. Gd₂O₃ play the network modifier role in the studied glasses and determines, by progressive addition, the increase of structural volume difference between the hypothetical crystalline compounds and the quenched samples. FTIR spectroscopy data show that the glass structure consists on the BiO₆, GeO₄ and GeO₆ structural units, and the conversion among these units mainly depends on the Gd₂O₃ content.     

Nonlinear optical effects in glasses containing copper chloride nanocrystals

Nonlinear optical properties of various glasses containing copper chloride nanocrystals have been studied at wavelengths of 532 and 1064 nm. It is established that the nonlinear optical response is manifested by the optical limiting of transmitted radiation and consists of two, low- and high-threshold parts. The low-threshold response is related to a self-defocusing of the radiation, while the high-threshold response is related to the phenomena of two-photon absorption, color center photogeneration, and thermal lens formation.     

Effect of the introduction of vanadium pentaoxide in phospho-tellurite glasses containing gadolinium ions

A range of phospho-tellurite glasses containing gadolinium was prepared and infrared absorption spectra were measured. Structural changes, as recognized by analyzing band shapes of IR spectra, revealed that Gd₂O₃ causes a higher extent of network polymerization as far as x ≤ 15 mol% because the conversion of [TeO₄] to [TeO₃] structural units is supported by the increase of metaphosphate structural groups. While for x between 20 and 30 mol% Gd₂O₃ show some drastic structural modifications which lead to the increase in the glass fragility. Thus the addition of V₂O₅ resulted in gradual depolymerization of the phosphate chains and formation of short phosphate units, which are linked to vanadium through P–O–V bonds. The formation of P–O–V bonds increases the cross-link between the phosphate chains and the bending mode of Te–O–Te or O–Te–O linkages.     

A XANES study of the valence state of vanadium in lithium vanadate phosphate glasses

Valence states of vanadium in Li₂O-V₂O₅-P₂O₅ electronic-ionic conducting glasses have been studied by X-ray absorption spectroscopy. The composition dependence of the XANES range of the spectra has been used to estimate relative abundance of the vanadium atoms in V⁴⁺ or V⁵⁺ charge states. This information is important for analysis of electronic transport in these glasses, which occurs via electronic hopping between aliovalent vanadium centers. It was found that in samples with the lowest V₂O₅ contents (10 mole% of V₂O₅) a vast majority of vanadium ions are in V⁴⁺ charge state. At higher V₂O₅ contents the proportion of V⁴⁺ ions decreases at the expense of V⁵⁺ ones, but remains substantial even in glasses with the highest contents of V₂O₅.     

Some optical and differential scanning calorimetry studies of sodium tetraborate glasses containing vanadium oxide

A series of glass samples was prepared from mixtures of Na₂B₄O₇ and V₂O₅. Measurements were made for infrared absorption and optical absorption spectra as a function of V₂O₅ content up to 10 mol%. The addition of V₂O₅ did not introduce any new absorption band as compared with the infrared spectrum of pure sodium tetraborate glass. The addition of V₂O₅ shifted the optical absorption edges towards lower energies, and introduced a new absorption band as compared with the optical absorption of pure Na₂B₄O₇ glass. Differential scanning calorimetry as a function of V₂O₅ content was also measured.     

A study of electron spin resonance in copper-phosphate glasses containing praseodymium

The e.s.r. spectra of glasses of compositions (P₂O₈)₆₅(CuO)_35–x (Pr₆O₁₁) and (P₂O₅)65(CuO)₂₅-(CaO)_10–x (Pr₆O₁₁) _x , wherex varied from 0 to 5 mol %, were measured. From the results and the chemical analyses of the samples it is found that the reduced valency ratioC of the copper in the glasses investigated generally increases with increasing Pr₆O₁₁ content. In our samples it is believed that enhanced chemical reduction of the cupric (Cu²⁺) ion is a consequence of its interaction with a reduced ion of the added praseodymium oxide.     

Structure,magnetic, and electrical studies on vanadium phosphate glasses containing different oxides

Glass system with molar composition (60% P₂O₅–30%V₂O₅–10%X) where X is Li₂O, Na₂O, K₂O, and BaO was prepared. The density and molar volume indicate that the density decreases while the molar volume increases with increasing ionic radius of doped oxides. IR studies reveal the coexistence of V⁴⁺ and V⁵⁺ ions (act as glass modifier and glass former, respectively). The observed paramagnetic behavior of samples indicates that V⁴⁺ > V⁵⁺ (the ratio V⁴⁺/V⁴⁺ + V⁵⁺ > 0.52 as obtained from chemical titration analysis). Mott’s model of conduction was applied to discuss DC electrical conduction mechanism. The prepared glass exhibits semiconducting behavior. However, Ba ion is the only ion which did not contribute to the ionic conduction. The conductivity increases with decreasing ionic radius of doped oxides due to high mobility due to their small size. The effect of hopping distance on the electrical conduction and magnetic properties were discussed. An attempt was done to determine the expected temperature of Ba ionic conduction and its ionic activation energy.     

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.     

A study of electron spin resonance of copper phosphate glasses containing tellurium oxide

Electron paramagnetic resonance in glasses of compositions (P₂O₅)_100–x-(CuO)_x and (P₂O₅)₅₀-(TeO₂)_50–x-(CuO)_x where x varied from 20 to 40 mol% has been investigated. The distribution of the copper between the two main valency states is determined from measurements of e.s.r. arising from the Cu²⁺ centres. The study of e.s.r. enables the distribution of copper in the glasses between the different valency states to be determined and thus indirectly provides evidence for hopping conduction in the glasses. From the results of e.s.r. and the chemical analysis of the samples it is found that the reduced valency ratioC, i.e. the ratio of the concentration of Cu⁺ ions to that of total copper in the glass, increases with increasing CuO content.     

Mössbauer and X-ray photoelectron spectroscopic studies of heat-treated calcium borate glasses containing iron

⁵⁷Fe Mössbauer and X-ray photoelectron spectroscopic studies have been carried out on a number of iron-containing calcium borate glasses which show large changes in d.c. conductivity upon annealing. The Mössbauer spectra of the unannealed glass samples are compatible with the presence of predominantly ferric iron in a six-co-ordinate oxygen environment. Upon annealing a partial ordering of the glassy phase is found as indicated by a reduction in the linewidth of the Mössbauer resonances. Longer annealing times lead to the precipitation ofα-Fe₂O₃ clearly identified by the gradual appearance of a six-line magnetically split pattern in the Mössbauer spectra. These changes are qualitatively correlated with changes in d.c. conductivity of the samples. The binding energies and full width at half maxima of representative core levels of each element present show a remarkable consistency for all samples. Moreover the 2p spectra of iron incorporated in the glassy phase are essentially similar to that of the precipitated Fe₂O₃.     

Raman spectroscopic study of hexavalent chromium in some silicate and borate glasses

The polarized Raman spectra of chromium-doped silicate and borate glasses have been measured and interpreted. It is shown that hexavalent chromium exists in silicate glasses as isolated chromate anions (CrO₄⁼). In binary sodium borate glasses there is a change of species from chromate to dichromate as the B₂O₃ concentration is increased.     

Thermodynamics of oxidation-reduction of vanadium in borate glasses

The V⁴⁺ V⁵⁺ equilibrium in a 2BaO-3B₂O₃ glass has been studied as functions of temperature, at a fixed partial pressure of oxygen, and total vanadium concentration of the melt. The optical and esr spectra of some of these glasses have also been studied to characterize the V⁴⁺ and V⁵⁺ centres. From the linear temperature dependence of the redox concentration ratio, the activation energy for the redox reaction has been determined at each concentration. The plot of logarithm of the ratio of the activity coefficients and also of the enthalpy of the redox reaction against composition showed considerable changes around 22 mol% V₂O₅. Structural changes associated with both V⁴⁺ and V⁵⁺ ions are suggested to account for such behaviour, which was also suggested from a previous study of the conductivity behaviour of such glasses. The optical and esr spectra showed considerable changes in the V⁴⁺-O and V⁵⁺-O bonding, but no sudden change was observed around 22 mol% V₂O₅.     

A study of the optical absorption edge in silicate glasses containing TiO2 oxide

A detailed study of the optical absorption as a function of temperature and composition for a series of soda-lime-silica glasses doped with TiO₂ oxide is presented. The variations of the optical energy gap with temperature in the range 296 to 483 K are reported. The UV results are analysed assuming optical absorption by indirect transitions. It was found from these optical absorption data that the present glass system can be divided into three compositional regions.     

Optical absorption of vanadium in sodium diborate glasses

The optical absorption in blown films and bulk specimens of sodium diborate glasses containing vanadium oxide based on the system [Na₂O-2B₂O₃]_1?x [V₂O₅] _x , wherex = 0, 0.05, 0.10, 0.15 and 0.20, has been studied in the wavelength range 200 to 900 nm. The fundamental absorption edge has been analysed in the light of the existing models. It is found that glasses containing a higher content of vanadium have fewer defects when compared with those containing a low vanadium content. The absorption spectra are interpreted as due solely to pentavalent vanadium.     

Electrical switching and spectroscopic studies of silver-vanado-phosphate glasses

High field electrical switching studies on x Ag₂O − (50−x) P₂O₅ −50V₂O₅ glasses have been carried out as a function of sample thickness, composition and temperature. The I–V characteristic show that switching in these glasses is memory type. The switch voltages are found to decrease with increase of temperature, on the other hand, the voltages increase with the thickness of the sample. The experimental findings clearly reveal that switching in these glasses is a thermally assisted bulk effect. The results obtained are explained on the basis of formation of crystalline conducting channels. Another notable observation is that the glass with 15 mol% Ag₂O concentration only exhibits the switching property at room temperature. This aspect is examined in view of various structural groups present in these glasses with the help of spectroscopic studies; IR and MAS–NMR measurements have been carried out. IR studies of these glasses show characteristic absorption peaks corresponding phosphate and vanadium vibrations in the network. ³¹P MAS–NMR chemical shift show presence of [POO_3/2]⁰ and [POO_2/2O]⁻ groups.