Synthesis and structural studies of Na<Subscript>2</Subscript>O-ZnO-ZnF<Subscript>2</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> oxyfluoride glasses

This paper describes the synthesis and spectroscopic studies of the glass system, 20Na₂O-(20-x) ZnO-xZnF₂-60B₂O₃(x = 0, 5, 10, 15, 20), prepared by melt quenching method. The analyses of DSC and XRD did not show the crystallinity of the glass sample. ¹¹B MAS-NMR shows the presence of sharp peak around −14 ppm. From the IR studies, the broadening of the peak around 1200–1400 and 800–1100 cm⁻¹ shows the presence of mixed linkages like B-O-B, B-O-Zn in the network.     

Luminescence of europium-doped BaO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

We have prepared europium-doped BaO-Bi2O₃-B2O₃ glasses and investigated the doping effect on the main physicochemical properties and local structure of the glasses. Using Judd-Ofelt analysis, we calculated intensity parameters (Ω₂, Ω₄, and Ω₆), spontaneous emission probabilities, the radiative lifetime, luminescence branching factors, the quantum yield of luminescence, and the stimulated emission cross sections for ⁵ D ₀ → ⁷ F _J transitions.     

Effect of Eu<Subscript>2</Subscript>O<Subscript>3</Subscript> doping on the crystallization behavior of BaO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

We gave studied the crystallization behavior of 30BaO · 25Bi₂O₃ · 45B₂O₃ glasses doped with Eu₂O₃ to different levels. At a Eu₂O₃ content of 7 mol % or higher, the glasses undergo volume crystallization. The only precipitating phase is a solid solution between europium and bismuth oxides. With increasing europium concentration in the glass, the structure of the crystallites changes from cubic to rhombohedral. We have investigated the morphology, physicochemical properties, and luminescence spectra of the glasses and glass-ceramics.     

Glass formation in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-BaO system

The physicochemical properties of BaO-Bi₂O₃-B₂O₃ glasses have been studied. The effect of KBF₄ additions on the properties of the glasses has been examined. The transmission of the glasses has been correlated with their local structure and composition.     

Preparation of magnetic composites through SrO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glass crystallization

Glasses with nominal compositions 11SrO · 5.5Fe₂O₃ · 4.5Al₂O₃ · 4B₂O₃ (1) and 15SrO · 5.5Fe₂O₃ · 4.5Al₂O₃ · 4B₂O₃ (2) were prepared by rapidly quenching oxide melts between counterrotating steel rollers. The glasses were then heat-treated in the range 650–950°C to produce glass-ceramic samples. The samples were characterized by X-ray diffraction, electron microscopy, and magnetic measurements. The phase composition of the glass-ceramics was determined, and their microstructure and magnetic properties were studied. The annealing temperature was shown to have a strong effect on the coercivity of the materials, which reaches 650 and 570 kA/m for compositions 1 and 2, respectively.     

Synthesis of nanocomposites based on MO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> (M = Ca,Sr, Ba) glasses

This work examines the effect of KBF₄ additions on the crystallization behavior of glasses based on the multicomponent systems MO-Bi₂O₃-B₂O₃ with M = Ca, Sr, and Ba. The glass-ceramic composites obtained contain a δ-Bi₂O₃-based crystalline phase with a crystallite size of ≃7 nm, evenly distributed over the glass matrix. The 400°C electrical conductivity of the nanocomposites reaches 2 × 10⁻⁴ S/cm, and the activation energy is 1.1 eV, typical of anion conduction. These values are comparable to those reported for δ-Bi₂O₃ ceramics.     

Calcium bismuth borates in the CaO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The 600°C (subsolidus) section of the CaO-Bi₂O₃-B₂O₃ phase diagram has been studied by x-ray diffraction and differential thermal analysis. A new calcium bismuth borate of composition CaBi₂B₄O₁₀ has been identified, and the existence of CaBi₂B₂O₇ has been confirmed. According to T-x phase diagram data, these compounds form peritectically at 700±5 and 783±5°C, respectively.     

Effect of secondary heat treatment on the spectroscopic properties of Na<Subscript>2</Subscript>O-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

We have studied the optical absorption and luminescence spectra of 45Na₂O · xNb₂O₅ · (55 − x)P₂O₅ glasses containing 5, 10, 20, 25, 30, and 35 mol % Nb₂O₅. The results indicate that the absorption band around 26000 cm⁻¹, responsible for the yellow color of the glasses, is due to the [Nb^(5+)--O⁻] center and disappears upon secondary heat treatment. Heat treatment of europium-doped glasses increases the concentration of Eu³⁺ centers in an asymmetric environment, which is accompanied by an increase in luminescence efficiency. The reason for this is that the Eu³⁺ ions are located outside the niobate subsystem of the glass matrix. The europium in the glasses studied acts as a protector ion.     

Characterization and electrical properties of semiconducting Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-K<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript> glasses

Semiconducting glasses of the Fe₂O₃-Bi₂O₃-K₂B₄O₇ system were prepared by the press-quenching method and their dc conductivity in the temperature range 223–393 K was measured. The glass transition temperature values (T_g) of the present glasses were larger than those of tellurite glasses. This indicates a higher thermal stability of the glass in the present system. The density for these glasses was consistent with the ionic size, atomic weight and amount of different elements in the glasses. Mössbauer results revealed that the relative fraction of Fe increases with increasing Fe₂O₃ content. Electrical conductivity showed a similar composition dependency as the fraction of Fe. The glasses had conductivities ranging from 10 to 10 Scm at temperatures from 223 to 393 K. Electrical conduction of the glasses was confirmed to be due to non-adiabatic small polaron hopping and the conduction was primarily determined by hopping carrier mobility.     

Electrical properties of some Y<Subscript>2</Subscript>O<Subscript>3</Subscript> and/or Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-containing lithium silicate glasses and glass-ceramics

The ac electrical properties of some lithium silicate glasses and glass-ceramics containing varying proportions of Y₂O₃ and/or Fe₂O₃ were measured to investigate their electronic hopping mechanism. There is a clear variation of these properties with composition. The obtained results were related to the concentration and role of Y₂O₃ and/or Fe₂O₃ in the lithium silicate glass structure. In crystalline solids the electrical properties data obtained were correlated to the type and content of the mineral phases formed as indicated by X-ray diffraction analysis (XRD). The conductivity, dielectric constant and dielectric loss of the studied glasses were studied using the frequency response in the interval 30 Hz–100 KHz and the effect of compositional changes on the measured properties was investigated. The measurements revealed that the electrical responses of the samples were different and complex. The addition of Y₂O₃ generally, decreased the ac conductivity, dielectric constant and dielectric losses of the lithium silicate glasses. The addition of Fe₂O₃ in Y₂O₃-containing glasses increases the conductivity, while, the dielectric constant and dielectric losses were found to be decreased. However, the addition of Fe₂O₃ instead of Y₂O₃ led to decrease the ac conductivity and increased their dielectric constant and dielectric losses. The obtained data were argued to the internal structure of the lithium silicate glass and the nature or role-played by weakness or rigidity of the structure of the sample. Lithium disilicate-Li₂Si₂O₅, lithium metasilicate-Li₂SiO₃, two forms of yttrium silicate Y₂Si₂O₇ & Y₂SiO₅, iron yttrium oxide-YFeO₃, lithium iron silicate-LiFeSi₂O₆ and α-quartz phases were mostly developed in the crystallized glasses. The conductivity of the crystalline materials was found to be relatively lower than those of the glass. At low frequency, as the Y₂O₃ content increased the ac conductivity, dielectric constant and dielectric loss data of the glass-ceramics decreased. However, the addition of Fe₂O₃ to the Y₂O₃ containing glass-ceramic led to increase the conductivity. The addition of high content of Fe₂O₃ instead of Y₂O₃ in the glass ceramic led to increase the ac conductivity.     

Study of structure and properties of ZnO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Glasses of the ternary system ZnO–Bi₂O₃–P₂O₅ were prepared and studied in two compositional series 50ZnO–xBi₂O₃–(50 − x)P₂O₅ and (50 − y)ZnO–yBi₂O₃–50P₂O₅. Two distinct glass-forming regions were found in the 50ZnO–xBi₂O₃–(50 − x)P₂O₅ glass series with x = 0–10 and 20–35 mol.% Bi₂O₃. All prepared Bi₂O₃-containing glasses reveal a high chemical durability. Small additions of Bi₂O₃ (∼5 mol.%) improve thermal stability of glasses. All glasses crystallize on heating within the temperature range of 505–583 °C. Structural studies by Raman and ³¹P MAS NMR spectroscopies showed the rapid depolymerisation of phosphate chains within the first region with x = 0–15 and the presence of isolated Q⁰ phosphate units within the second region with x = 20–35. Raman studies showed that bismuth is incorporated in the glass structure in BiO₆ units and their vibrational bands were observed within the spectral region of 350–700 cm⁻¹. The evolution of properties and the spectroscopic data are both in accordance with a network former effect of Bi₂O₃.     

Effect of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> on the crystallization behavior of SiO<Subscript>2</Subscript>–MgO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

A series of glass comprising of SiO₂–MgO–B₂O₃–Y₂O₃–Al₂O₃ in different mole ratio has been synthesized. The crystallization kinetics of these glasses was investigated using various characterization techniques such as differential thermal analysis (DTA), thermo gravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Crystallization behavior of these glasses was markedly influenced by the addition of Y₂O₃ instead of Al₂O₃. Addition of Y₂O₃ increases the transition temperature, T _g, crystallization temperature, T _c and stability of the glasses. Also, it suppresses the formation of cordierite phase, which is very prominent and detrimental in MgO-based glasses. The results are discussed on the basis of the structural and chemical role of Y³⁺ and Al³⁺ ions in the present glasses.     

Spectral diagnostics of vapor composition over molten Na<Subscript>2</Subscript>WO<Subscript>4</Subscript> and Na<Subscript>2</Subscript>O-BaO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The high-temperature Raman spectra recording technique was found applicable also to study luminescence of atoms and individual molecular groups in vapors over some overheated molten compounds. Sodium atomic luminescence excited with a yellow (578.2 nm) copper vapor laser line was detected in vapors over overheated molten Na₂WO₄ and Na₂O-BaO-B₂O₃ system. The possibility of recording the sodium doublet spectrum by excitation with the 578.2 nm copper vapor laser line in vapors of any melts containing sodium was shown. Overheated melts in the Na₂O-BaO-B₂O₃ system disproportionate and lose boron oxide as evidenced by the recording of luminescent spectra of BO₂ molecular radicals in vapors over relevant melts.     

Effect of crucible material on optical bandgap and activation energy of Na<Subscript>2</Subscript>O-CdO-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

In the sodium cadmium phosphate glasses, the effect of diffused alumina from alumina crucible has been assessed by measuring various properties such as mass density, refractive index, optical bandgap and dc conductivity. The results of measurements corresponding to glasses prepared in alumina crucible have been compared with those of glasses prepared in platinum crucible with and without adding Al₂O₃. The Optical bandgap and direct current (dc) electrical conductivity of the Na₂O-CdO-P₂O₅ glasses prepared in alumina and platinum crucibles have been determined at room temperature. These glasses have also been electrically characterised in the temperature range 293–423 K. Activation energy E_a of the samples prepared in alumina crucible lies in the range 0.60–0.96 eV whereas it stands in the range of 0.57–0.94 eV for the samples prepared in platinum crucible.     

Electrical properties of V<Subscript>2</Subscript>O<Subscript>5</Subscript>-CaO-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses exhibiting majority charge carrier reversal

The thermoelectric power and d.c electrical conductivity of x V₂O₅⋅40CaO⋅(60−x)P₂O₅ (10 ≤ x ≤ 30) glasses were measured. The Seebeck coefficient (Q) varied from +88 μ V K⁻¹ to −93 μV K⁻¹ as a function of V₂O₅ mol%. Glasses with 10 and 15 mol% V₂O₅ exhibited p-type conduction and glasses with 25 and 30 mol% V₂O₅ exhibited n-type conduction. The majority charge carrier reversal occurred at x = 20 mol% V₂O₅. The variation of Q was interpreted in terms of the variation in vanadium ion ratio (V^{5 +}/V^{4 +}). d.c electrical conduction in x V₂O₅⋅40CaO⋅(60−x)P₂O₅ (10 ≤ x ≤ 30) glasses was studied in the temperature range of 150 to 480 K. All the glass compositions exhibited a cross over from small polaron hopping (SPH) to variable range hopping (VRH) conduction mechanism. Mott parameter analysis of the low temperature data gave values for the density of states at Fermi level N (E_F) between 1.7 × 10²⁶ and 3.9 × 10²⁶ m⁻³ eV⁻¹ at 230 K and hopping distance for VRH (R_VRH) between 3.8 × 10⁻⁹m to 3.4 × 10⁻⁹ m. The disorder energy was found to vary between 0.02 and 0.03 eV. N (E_F) and R_VRH exhibit an interesting composition dependence.     

Electrical conductivity of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Tm<Subscript>2</Subscript>O<Subscript>3</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> solid solutions

New solid solutions, Bi_2?x?y Tm _x Nb _y O_3+δ, with tetragonal and cubic structures have been synthesized in the Bi₂O₃-Tm₂O₃-Nb₂O₅ system, and their electrical conductivity has been measured at temperatures from 670 to 1020 K. The 1020-K conductivity of the tetragonal solid solution Bi_1.8Tm_0.15Nb_0.05O_3+δ is comparable to that of Bi_1.75Tm_0.25O₃, the best conductor in the Bi₂O₃-Tm₂O₃ system.     

Gamma rays interactions with Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-doped Na<Subscript>2</Subscript>O–CdO–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses assessed by collective optical and FT infrared absorption spectroscopy

Undoped and Bi₂O₃-doped glasses from the system Na₂O–CdO–P₂O₅ were prepared and studied through investigating their optical and FTIR spectra before and after gamma irradiation beside measuring their thermal expansion properties. Optical spectra reveal distinct UV absorption with additional peaks upon introducing Bi₂O₃ added with different concentrations from 1 to 7.5%. The UV absorption of the undoped sample is related to trace iron impurities while the extended UV absorption peaks are correlated with absorption of Bi³⁺ ions. FTIR spectra show condensed phosphate groups (Q², Q³ units) beside the sharing of bismuth ions in their vibrational sites. Gamma irradiation causes limited changes in the UV spectra but involves the generation of an induced visible band in the undoped glass. These changes are assumed to be due to some suggested photochemical reactions on the trace iron impurities and the formation of an induced visible (POHC) band on the phosphate network. Careful inspection of the selected deconvoluted spectra for the undoped glass and doped (7.5 wt%) supports the introduced assumptions. The thermal expansion parameters are correlated with the type of bonding of bismuth ions within the network structure.     

Preparation and characterization of bioactive sol-gel-derived Na<Subscript>2</Subscript>Ca<Subscript>2</Subscript>Si<Subscript>3</Subscript>O<Subscript>9</Subscript>

In this study, pure Na₂Ca₂Si₃O₉ was synthesized by a sol-gel method, and Na₂Ca₂Si₃O₉ cuboids and disks were prepared by uniaxial pressing and calcining at 700 °C. The porosity and mechanical strength of the Na₂Ca₂Si₃O₉ cuboids were measured, and the results showed that the Na₂Ca₂Si₃O₉ cuboids were porous with an average porosity of 44%, and the 3-point bending strength of the cuboids was 6.08 MPa. The in vitro bioactivity of Na₂Ca₂Si₃O₉ was carried out by soaking Na₂Ca₂Si₃O₉ disks in simulated body fluid (SBF). The results showed that hydroxyapatite (HA) formed on the surface of Na₂Ca₂Si₃O₉ samples after soaking for 1 day, which indicated good bioactivity of Na₂Ca₂Si₃O₉.