Piezoelectric and elastic properties of ZnF2–PbO–TeO2: TiO2 glass ceramics

Piezoelectric coefficients d₃₃ as well as ultrasonic velocities and elastic coefficients of ZnF₂–PbO–TeO₂ glasses crystallized with different concentrations of TiO₂ (0.5 to 2.0 wt.%) were measured. The contribution to the piezoelectric coefficients is attributed to presence of Pb₅Ti₃F₁₉, PbTiO₃ and PbTeO₃ ferroelectric crystal phases. The piezoelectric coefficients show substantial sensitivity to presence of TiO₂. The ultrasonic velocities and the related elastic coefficients in these glass ceramics as a functions of concentration of nucleating agent TiO₂ exhibited minimal effect at 1.0 wt.%. This is ascribed to the larger presence of titanium ions in Ti³⁺ states which act as modifiers and finally de-polymerize glass ceramic network. The results have been further discussed quantitatively within a framework of different oxidation states of titanium ions and the nature of the crystal phases ingrained in the glass ceramic.     

Influence of Bi2O3 content on the crystallization behavior of TeO2–Bi2O3–ZnO glass system

Glass ceramic materials with composition 75TeO₂–xBi₂O₃–(25-x)ZnO (x = 13, 12, 11) possessing transparency in the near- and mid-infrared (MIR) regions were studied in this paper. It was found that as the Bi₂O₃ content increased in the glass composition, the observed crystallization tendency is enhanced, and high crystal concentrations were obtained for the glasses with high Bi₂O₃ content while maintaining transparency in the MIR region. Crystal size in the glass ceramic was reduced by adjusting the heat treatment conditions; the smallest average size obtained in this study is 700 nm. Bi_0.864Te_0.136O_1.568 was identified using X-ray Diffraction (XRD) and found to be the only crystal phase developed in the glass ceramics when the treatment temperature was fixed at 335 °C. The morphology of the crystals was studied using Scanning Electron Microscopy (SEM), and crystals were found to be polyhedral structures with uniform sizes and a narrow size distribution for a fixed heat treatment regime. Infrared absorption spectra of the resulting glass ceramics were studied. The glass ceramic retained transparency in the infrared region when the crystals inside were smaller than 1 μm, with an absorption coefficient less than 0.5/cm in the infrared region from 1.25 to 2.5 μm. The mechanical properties were also improved after crystallization; the Vickers Hardness value of the glass ceramic increased by 10% relative to the base glass.     

Mechanism of crystallization of fast fired mullite-based glass–ceramic glazes for floor-tiles

The mechanism of crystallization from a B₂O₃-containing glass, with composition based in the CaO–MgO–Al₂O₃–SiO₂ system, to a glass–ceramic glaze was studied by different techniques. Glass powder pellets were fast heated, simulating current industrial tile processing methods, at several temperatures from 700 to 1200 °C with a 5 min hold. Microstructural study by field emission scanning electron microscopy revealed that a phase separation phenomenon occurred in the glass, which promoted the onset of mullite crystallization at 900 °C. The amount of mullite in the glass heated between 1100 and 1200 °C was around 20 wt%, as determined by Rietveld refinement. The microstructure of the glass–ceramic glaze heated at 1160 °C consisted of interlocked, well-shaped, acicular mullite crystals longer than 4 μm, immersed in a residual glassy phase.     

Effects of Fe2O3 replacement of ZnO on elastic and structural properties of 80TeO2–(20 − x)ZnO–xFe2O3 tellurite glass system

Ternary tellurite glasses with the chemical formula 80TeO₂–(2 ? x)ZnO–xFe₂O₃ (x = 0–15 mol%) have been prepared by the melt-quenching method. Elastic and structural properties of the glasses were investigated by measuring both longitudinal and shear velocities using the pulse-echo overlap method at 5 MHz and Fourier transform infrared (FTIR) spectroscopy, respectively. Both longitudinal and shear velocity showed a large increase of 3.40% and 4.68%, respectively, at x = 5 mol% before a smaller increase for x > 5 mol%. Interestingly, longitudinal modulus (L), shear modulus (G), bulk modulus (K) and Young's modulus (E) recorded similar trends with increase in Fe₂O₃. The initial large increases in shear and longitudinal velocity and related elastic moduli observed at x = 5 mol% are suggested to be due to structural modification which enhances rigidity of the glass network. FTIR analysis showed increase in bridging oxygen (BO) as indicated by the relative intensity of the TeO₄ assigned peaks and increase in intensity of the FeO₆ assigned peak (~ 451 cm^? 1) which indicates that Fe acts as a modifier in the glass network. The increase in rigidity of the glass system is suggested to be due to the increase of BO together with the formation of strong covalent FeO bond. Quantitative analysis based on the bulk compression and ring deformation models showed that the k_bc/k_exp value decreased gradually from 2.41 (x = 0 mol%) to 2.02 (x = 15 mol%) which infers that the glass system became a relatively more open 3D network as Fe₂O₃ was increased.     

Non-isothermal crystallization kinetic studies on MgO–Al2O3–SiO2–TiO2 glass

Thermal stability and crystallization kinetics of the glass 21% MgO, 21.36% Al₂O₃, 53.32% SiO₂ and 4.11% TiO₂ (mol%) has been studied using differential thermal analysis (DTA), dilatometry and X-ray diffraction (XRD). Glass in both bulk and frit forms were produced by melting in platinum crucible at 1600 °C for 1–2 h. From variation of DTA peak maximum temperature with heating rate, the activation energies of crystallization were calculated to be 340 kJ mol⁻¹ and 498 kJ mol⁻¹ for first and second crystallization exotherms, respectively. Crystallization of bulk glass was carried out at various temperatures and for different time durations in the range of 850–1000 °C. The influence of the addition of TiO₂ on the crystallization sequence of the glass was experimentally determined and discussed.     

Studies of nanostructuring in cesium magnesium tungsten phosphate glass

Cs₂O–MgO–WO₃–P₂O₅ glass was examined in a broad temperature range using heat capacity, Raman and Brillouin scattering methods. The main aim was to study the elastic properties of the as-prepared glass, the mechanism of nanostructuring in this material and the influence of nanostructuring on its elastic properties. It was shown that this glass exhibits prominent nanocrystallization during thermal treatment, giving Cs(Mg_0.25W_1.75)O₆ nanocrystals with the size of 4–10 nm. The crystallization process was hindered when crystallinity reached about 14 ± 0.6 wt%. The origin of this behavior was discussed. It was also demonstrated that the elastic properties are largely improved by nanocrystallization.     

Preparation and spectral properties of Nd3 +-doped transparent glass ceramic containing Ca5(PO4)3F nanocrystals

A Nd^3 +-doped transparent oxyfluoride glass ceramic containing Ca₅(PO₄)₃F nanocrystals was prepared by thermal treatment at the crystallization temperature for the precursor glass. The transmittances of the precursor glass and the glass ceramic with a thickness of about 2 mm are up to 84.7% and 77.4% in the visible range. The volume fraction of Ca₅(PO₄)₃F nanocrystals in the glass ceramic is about 19% and the ingress fraction of Nd^3 + ions into the Ca₅(PO₄)₃F nanocrystals is about 32%. The peak absorption cross-section increases to 224% at 807 nm and the full width at half maximum for the 807 nm band decreases from 17.5 to 3.5 nm after the crystallization process. The peak stimulated emission cross-section increases from 1.89 × 10^? 20 to 2.42 × 10^? 20 cm² at 1062 nm and the effective width of the emission line for the 1062 nm band decreases from 34 to 29 nm after the crystallization process. The improvement of spectroscopic properties indicates that the glass ceramic is potentially applicable as the 1.06 μm laser material.     

Preparation and ionic conductivity of transparent glass−ceramics containing a large quantity of lithium−mica

In order to crystallize a large quantity of the lithium?mica in glass?ceramics, 5.1 mass% MgF₂ was added to the starting materials of the parent glasses having chemical compositions of Li_(1+x)Mg₃AlSi_3(1+x)O_10+6.5xF₂ (x = 0.5 and 1.0). Transparent glass?ceramics, in which a large quantity of lithium?mica with particle size of <50 nm was separated, could be prepared from the MgF₂-added parent glass with x = 0.5. While the parent glass, which had a binodal phase separation structure, did not exhibit electrical conductivity, the transparent glass–ceramic was given conductivity by the formation of an interlocking structure of mica. As the separated mica formed a tighter interlocking structure, the conductivity increased and reached a value of 2.0 × 10^?3 S/cm at 600 °C. The MgF₂-added parent glass with x = 1.0 was not transparent because of coarse spinodal phase separation. The conductivity was 4.3 × 10^?4 S/cm at 600 °C but was significantly decreased by the separation of mica.     

The effect of TiO2 on phase separation and crystallization of glass-ceramics in CaO–MgO–Al2O3–SiO2–Na2O system

The experiments were carried out on studying the effect of phase separation on nucleation and crystallization in the glass based on the system of CaO–MgO–Al₂O₃–SiO₂–Na₂O. In the experiments, TiO₂ was chosen as nucleating agent. Three batches of 5, 8 and 10 wt% TiO₂ substitution were investigated by the techniques of DSC, XRD, FTIR and FESEM equipped with EDS. XRD and FTIR analysis indicated that the super cooled glasses were all amorphous, the heat treatment leading to nucleation would cause a disruption of silica network which followed phase separation. The phase separation followed the generation of crystal seeds Mg(Ti, Al)₂O₆. FESEM observation and EDS analysis revealed that the more TiO₂ content of glass, the more droplet separated phase and crystal seeds after nucleation heat treatment. The main crystal phase is clinopyroxene, Ca(Ti, Mg, Al)(Al, Si)O₆, of crystallized glass.     

Aluminoborate and aluminoborosilicate glasses with high chemical durability and the effect of P2O5 additions on the properties

Several series of SrTiO₃–aluminoborate and SrTiO₃–aluminoborosilicate glasses were prepared, which exhibited low corrosion rates in water at 90 °C. The additions of up to 9 mol% P₂O₅ to these glasses were found to significantly improve the chemical durability. The weight loss rate of a glass with the nominal composition (mol%) 15SrO–15TiO₂–23.3Al₂O₃–46.7B₂O₃ decreased by over two orders of magnitude with the additions of up to 9 mol% P₂O₅. In contrast, P₂O₅-additions increased the dissolution rate of the silicate analog of the initial borate glass, 15SrO–15TiO₂–23Al₂O₃–47SiO₂. The positive effect of small P₂O₅ additions on the chemical durability of the aluminoborate glasses may be attributed to the replacement of BO₃ units by BO₄ units in the glass network, as indicated by infrared and Raman spectra.     

Morphology and dispersion state of Ba2TiSi2O8 nanocrystals in transparent glass-ceramics and their nanoindentation behavior

The morphology and dispersion state of Ba₂TiSi₂O₈ (BTS) nanocrystals in transparent glass-ceramics (composition: 40BaO–20TiO₂–40SiO₂) were examined from high resolution transmission electron microscope observations, and their nano-scale deformation behavior was examined using Berkovich nanoindentation technique (standard-type and continuous stiffness measurement (CSM)-type). In the early stage of crystallization, BTS crystalline layers with a thickness of ~ 120 nm were formed at the surface and ellipsoid-shaped crystallites with a diameter of 100–200 nm were dispersed in the glass matrix. In the late stage, BTS crystals with a diameter of 200–400 nm were formed densely, but a glassy phase was present between BTS crystals. The Young's modulus evaluated from CSM-type nanoindentation measurements for a deformation scale of about 100 nm shows the values of 98 GPa for the glass and 110 GPa for the glass-ceramics with nanocrystals. It was suggested that CSM-type measurements are very sensitive in the nano-scaled homogeneity in the heat-treated samples.     

Structure and non-linear optical properties of BaO–TiO2–SiO2 glass containing Ba2TiSi2O8 crystal

The BaO–TiO₂–SiO₂ crystallized glass containing Ba₂TiSi₂O₈ crystal phase was examined using X-ray diffraction (XRD) measurement and Maker fringe technique. It has been found that the crystallized glasses with a composition of close to the stoichiometric Ba₂TiSi₂O₈ showed bulk crystallization, whereas other crystallized glasses with non-stoichiometric composition of Ba₂TiSi₂O₈ showed surface crystallization. The parameter ΔT, the difference in temperature between the crystallization onset and the glass transition temperature, strongly affects the crystallization behaviors of the present BTS glasses. The 30BaO–20TiO₂–50SiO₂ transparent surface crystallized glass with strong c-oriented Ba₂TiSi₂O₈ phase showed its second-order non-linear optical constant, d₃₃ = 6.1 pm/V.     

Chemical durability and weathering resistance of canasite based glass and glass-ceramics

Classic composition 8.4Na₂O·5K₂O·10.8CaO·64SiO₂·10.5CaF₂·1.3Al₂O₃ (G1/GC1) and high silicon composition 7.6Na₂O·4K₂O·8.4CaO·71SiO₂·8CaF₂·1.0Al₂O₃ (G2/GC2) canasite-based glass and glass-ceramics were prepared, and the chemical durability and weathering of samples were studied with XRD, ICP-AES, SEM and optical microscopy. Interestingly, a kind of color fringe pattern caused by the acid leaching was directly observed on the glass ceramic surface under optical microscopy. The 20 day weight losses of glass and glass ceramic in acid (1 M HCl) and alkali (1 M NaOH/1 M Na₂CO₃) solution were measured. Accelerated weathering was used to demonstrate that increasing silicon content contributes to the weathering performance of glass and glass-ceramics. For different micro-structures and compositions, the weight loss of each glass and glass-ceramic is quite different. In general, through increasing the network interconnectivity of residual glass network and suppressing the crystallization of the less durable canasite phase, the addition of SiO₂ (from 60 mol% to 71 mol%) enhanced the chemical durability of canasite-based glass and glass ceramic relatively under acid, alkali and weathering conditions.     

Na2CaSi2O6–P2O5 based bioactive glasses. Part 1: Elasticity and structure

The glass structure and elastic properties of two bioglasses having bulk compositions near Na₂CaSi₂O₆ (45S5.2) and Na₂CaSi₃O₈ (55S4.1) were studied using both Raman and Brillouin scattering techniques. The annealed 45S5.2 glass has more Q² and Q⁰ but less Q³ species than 55S4.1 glass due to lower (Si⁴⁺ + P⁵⁺)/(Na⁺ + Ca²⁺) ratio. Brillouin scattering measurements of the as-annealed glasses indicated that 45S5.2 glass is ca. 2% and 9% higher in Young’s and bulk moduli than 55S4.1 glass due to more modifiers in the 45S5.2 glass. Nearly full crystallization of 45S5.2 glass was observed after treating it at 715 °C for ca. 30 min. Devitrification of the 45S5.2 glass caused an increase in the elastic moduli up to ca. 30% (fully crystallized) but a negligible change in density. This 45S5.2-derived crystalline phase displayed at least 17 Raman bands, and has the average elastic moduli of 72.4 (bulk), 41.6 (shear), and 104.7 (Young’s) GPa. The comparable elastic moduli with hydroxyapatite and the ability for developing a HCA layer in simulated body fluid indicate that the 45S5.2-derived phase may be better for using as a substitute of bone than its parent glass.     

Effect of Mo–Fe substitution on glass forming ability and thermal stability of Fe–C–B–Mo–Cr–W bulk amorphous alloys

Amorphous Fe_67?xC₁₀B₉Mo_7+xCr₄W₃ (x = 1–7 at.%) plates with 0.64 mm thickness were prepared by copper mold casting. The thermal properties and microstructural development during heat treatments were investigated by a combination of differential scanning calorimetry, differential thermal analysis, and X-ray diffraction. The glass forming ability (GFA) and activation energy for crystallization have a distinct dependence on Mo content. Fe₆₂C₁₀B₉Mo₁₂Cr₄W₃ was the best glass former in this study, demonstrating a supercooled liquid region, ΔT_x = 51 K, and an activation energy for crystallization, Q = 453 kJ/mol. The GFA of alloys in this system was governed by elastic strain optimization resulting directly from the variation in Mo content. Heat treatments were performed to demonstrate resistance to crystallization under typical processing conditions. Alloys in this system exhibited a three phased evolution during crystallization. A second set of heat treatments was performed to identify each phase. An analysis of phase evolution revealed a distinct dependence of phase evolution with stepwise substitution of Mo for Fe in this system.     

Thermal and mechanical properties of rare earth aluminate and low-silica aluminosilicate optical glasses

Aluminate glasses containing 45–71.5 mol% alumina, 10–40 mol% rare earth oxide, and 0–30 mol% silica were synthesized from precursor oxides. The glass transition and crystallization temperatures were determined by differential scanning calorimetry; the structural and mechanical properties were investigated by Raman and Brillouin spectroscopy. The range of the supercooled liquid region varies from ∼40 °C to 200 °C, providing a useful working range for compositions with 5–30 mol% silica. Raman scattering showed the presence of isolated SiO₄ species that strengthen the network-forming structure, enhance glass formation, and stabilize the glass even when they are present at fairly low concentrations. Sound velocities were measured by Brillouin scattering. From these and other values, various elastic moduli were calculated. The moduli increased with both aluminum and rare earth content, as did the hardness of the glasses. Young’s modulus was in the range 118–169 GPa, 60–130% larger than that for pure silica glass.     

Effects of modifier additions on the thermal properties,chemical durability,oxidation state and structure of iron phosphate glasses

Modified iron phosphate glasses have been prepared with nominal molar compositions [(1?x)·(0.6P₂O₅–0.4Fe₂O₃)]·xR_ySO₄, where x = 0–0.5 in increments of 0.1 and R = Li, Na, K, Mg, Ca, Ba, or Pb and y = 1 or 2. In most cases the vast majority or all of the sulfate volatalizes and quarternary P₂O₅–Fe₂O₃–FeO–R_yO_z glasses or partially crystalline materials are formed. Here we have characterized the structure, thermal properties, chemical durability and redox state of these materials. Raman spectroscopy indicates that increasing modifier oxide additions result in depolymerization of the phosphate network such that the average value of i, the number of bridging oxygens per –(PO₄)– tetrahedron, and expressed as Qⁱ, decreases. Differences have been observed between the structural effects of different modifier types but these are secondary to the amount of modifier added. Alkali additions have little effect on density; slightly increasing T_g and T_d; increasing α and T_liq; and promoting bulk crystallization at temperatures of 600–700 °C. Additions of divalent cations increase density, α, T_g, T_d, T_liq and promote bulk crystallization at temperatures of 700–800 °C. Overall the addition of divalent cations has a less deleterious effect on glass stability than alkali additions. ⁵⁷Fe Mössbauer spectroscopy confirms that iron is present as Fe²⁺ and Fe³⁺ ions which primarily occupy distorted octahedral sites. This is consistent with accepted structural models for iron phosphate glasses. The iron redox ratio, Fe²⁺/ΣFe, has a value of 0.13–0.29 for the glasses studied. The base glass exhibits a very low aqueous leach rate when measured by Product Consistency Test B, a standard durability test for nuclear waste glasses. The addition of high quantities of alkali oxide (30–40 mol% R₂O) to the base glass increases leach rates, but only to levels comparable with those measured for a commercial soda-lime-silica glass and for a surrogate nuclear waste-loaded borosilicate glass. Divalent cation additions decrease aqueous leach rates and large additions (30–50 mol% RO) provide exceptionally low leach rates that are 2–3 orders of magnitude lower than have been measured for the surrogate waste-loaded borosilicate glass. The P₂O₅–Fe₂O₃–FeO–BaO glasses reported here show particular promise as they are ultra-durable, thermally stable, low-melting glasses with a large glass-forming compositional range.     

Enhanced mid-IR luminescence of Tm3+ ions in Ga2S3 nanocrystals embedded chalcohalide glass ceramics

Chalcohalide glass with a composition of 65GeS₂–25Ga₂S₃–10CsI (in mol%) doped with 0.6 wt% Tm³⁺ ions was prepared by conventional melt–quench method. By heat treating the precursor glass at 20 °C above its glass transition temperature T_g for different durations, IR transparent glass ceramics were obtained. X-ray diffraction (XRD) and scanning electron microscope (SEM) showed that Ga₂S₃ crystallites were precipitated after heat treatment and their grain sizes were in nano-scale and increased with the elongation of heat treated time. Mid-IR luminescence properties of the glass and transparent glass ceramic samples were investigated. The emissions at 2.3 and 3.8 μm corresponding to optical transitions of ³H₄ → ³H₅ and ³H₅ → ³F₄ of Tm³⁺ ions were significantly enhanced by the presence of Ga₂S₃ nanocrystals and reached a maximum after 8 hours treatment.     

Glass-ceramics in the system BaO/TiO2(ZrO2)/Al2O3/B2O3 and their thermal expansion

Glasses in the system BaO/TiO₂(ZrO₂)/Al₂O₃/B₂O₃ were melted from the raw materials with and without the addition of platinum. They were crystallized in two steps at 720 and 780 °C. TiO₂ does not act as nucleating agent in this system, but widely prevents crystallization. Samples additionally doped with platinum show the crystallization of BaAl₂B₂O₇. However, samples containing equimolar quantities of TiO₂ and ZrO₂ showed the crystallization of this phase without the addition of platinum. The thermal expansion coefficients of samples with TiO₂-concentration ⩽7 mol% or TiO₂/ZrO₂-concentrations ⩽5 mol% exhibit zero or even slightly negative thermal expansion coefficients.     

Preparation of Nd2O3-doped calcium aluminosilicate glasses and thermo-optical and mechanical characterization

The calcium aluminosilicate glass (CAS) is an important class of optical materials due to the many applications envisaged, including its use as active media for glass lasers. In order to study how Nd₂O₃ doping affects the mechanical and the thermo-optical properties of CAS glass, two series of CAS glass, doped with Nd₂O₃ up to 5 wt%, were prepared in a vacuum atmosphere. The rare earth changes the physical properties, and this influence of doping ion content is discussed for both the series of samples in terms of mechanical, thermal, and thermo-optical properties. The study analyzed hardness and elastic moduli, glass transition temperature, crystallization temperature, thermal diffusivity, specific heat, density, thermal conductivity, refractive index, and thermo-optical properties, like temperature coefficient of the optical path length (dS/dT). The results presented provide information about the sample’s structure, and show that for Nd₂O₃ concentration up to 5 wt% there were no significant changes in the glass host material.