Microstructural analysis of Ga2S3–2MCl (M = K, Rb, Cs) glasses using Raman scattering

Raman scattering spectra of Ga₂S₃–2MCl (M = K, Rb, Cs) glasses have been conducted at room temperature. Based on the analysis of the local co-ordination surroundings of Cs⁺ ions, the similarities and differences of Raman spectra for the glass Ga₂S₃–2CsCl and the bridged molecular GaCl₃ were explained successfully. Through considering the effect of M⁺ ions on mixed anion units [GaS_4?xCl_x] and bridged units [Ga₂S_6?xCl_x] and the corresponding microstructural model, the Raman spectral evolution of the Ga₂S₃–2MCl (M = K, Rb, Cs) glasses was reasonably elucidated.     

Optical band gap and Raman spectra in some (Bi2O3)x(WO3)y(TeO2)100−x−y and (PbO)x(WO3)y(TeO2)100−x−y glasses

The glasses representing (Bi₂O₃)_x(WO₃)_y(TeO₂)_100?x?y and (PbO)_x(WO₃)_y(TeO₂)_100?x?y systems were prepared. The dilatometric glass-transition temperatures of examined glass samples were found in the region 383–434 °C, the coefficient of thermal expansion varied from 12 to 16 ppm/°C and the density ranged from 6.30₂ to 6.80₈ g/cm³. From the optical transmission measurements of thin glassy bulk samples prepared by a glass blowing, the optical gap values were found in the narrow region 3.21–3.36 eV. For the temperature interval 300–480 K, the values of the temperature coefficient of the optical band gap varied from 3.7 × 10^?4 to 5.24 × 10^?4 eV/K. It is suggested that Raman feature observed at around 350 cm^?1 can be assigned to an overlap of Raman bands attributed to WO₆ corner shared octahedra and to the following three atomic linkages: Bi–O–Te, Pb–O–Te and W–O–Te.     

The preparation and structural studies in the (80 − x)TeO2–20ZnO–(x)Er2O3 glass system

Er³⁺-doped tellurite glasses of the (80 ? x)TeO₂–20ZnO–(x)Er₂O₃ system (0.5 mol% ? x ? 2.5 mol%) have successfully been made by melt-quenching technique and their structure has been investigated by means of DTA and Raman spectroscopy. The DTA results show the thermal parameters; such as the glass transition temperature (T_g) and crystallization temperature (T_c) were determined. It is found that this system provides a stable and wide glass formation range in which the glass stability around 99–140 °C may be obtained. The Raman spectroscopy used the structural studies in the glass system. Two Raman shift peaks were observed around 640–670 cm^?1 and 720–740 cm^?1, which correspond to the stretching vibration mode of TeO₄ tbp and TeO₃ tp, respectively. It is found that the spectral shift in Raman spectra is depending on the Er₂O₃ content. This evolution is an indication of the changes in the basic unit of the glass structure.     

Thermal and optical properties of TeO2–ZnO–BaO glasses

We report the results of a systematic study of the thermal and optical properties of a new family of tellurite glasses, TeO₂–ZnO–BaO (TZBa), as a function of the barium oxide mole fraction and compare them with those of TeO₂–ZnO–Na₂O (TZN). The characteristic temperatures of this new glass family (glass transition, T_g, crystallization, T_x, and melting, T_m) increase significantly with BaO content and the glasses are more thermally stable (greater ΔT = T_x ? T_g) than TZN glasses. Relative to these, Raman gain coefficient of the TZBa glasses also increases by approximately 40% as well as the Raman shift from ~ 680 cm^? 1 to ~ 770 cm^? 1. The latter shift is due to the modification of the glass with the creation of non-bridging oxygen ions in the glass network. Raman spectroscopy allows us to monitor the changes in the glass network resulting from the introduction of BaO.     

Vibrational spectroscopy study of niobium germanosilicate glasses

A series of glasses in the (Ge,Si)O₂–Nb₂O₅–(Na,K)₂O system were prepared by melting and casting. Their density and characteristic temperatures were determined by Differential Thermal Analysis (DTA) and their structure was analyzed by infrared and polarized Raman spectroscopies. DTA data have indicated an increased glass thermal stability with the replacement of GeO₂ by SiO₂. Kramers–Kronig analysis of the infrared specular reflectance data indicated a strong ionic character for the germanosilicate glasses. The Raman spectra of germanosilicate compositions were generally dominated by an intense Boson peak at ∼72 cm⁻¹ and a high frequency, polarised peak at ∼880 cm⁻¹, related to NbO₆ octahedra with at least one non-bridging oxygen. The germanosilicate structure appears to be formed by alternating GeO₄ tetrahedra and NbO₆ octahedra, in addition to SiO₄ tetrahedra.     

Preparation of Cu2ZnSnS4 single crystals from Sn solutions

We investigated the phase diagrams of the Cu₂ZnSnS₄ (CZTS)–Sn pseudobinary system in order to obtain knowledge useful for the growth of high-quality CZTS single crystals using a solution-based method. For Sn solutions saturated with less than ～60 mol% CZTS, the solutes are separated into two phases (CZTS phase+SnS_x phase+liquid phase). On the other hand, for solutions with more than 60 mol% CZTS, the solutes are single phase (CZTS phase+liquid phase). The CZTS single crystals were obtained from a 70 mol% CZTS solution (liquid temperature 850 °C) at 900 °C. The powder X-ray diffraction (XRD) pattern of the CZTS single crystal shows preferred orientations of (112), (220) and (312) planes, confirming the Kesterite structure of CZTS. The Raman spectrum shows three peaks at 287, 338, 371 cm^?1, which corresponded to CZTS peaks. The composition of the CZTS single crystal along the growth direction is found to be slightly Cu-poor, Zn-rich and S-rich. Therefore, it is assumed that the Cu vacancy is the dominant p-type conduction mechanism.     

Glass formation of Ti–Ni–Sn ternary alloys correlated with TiNi–Ti3Sn pseudo binary eutectics

Glass-forming ability (GFA) of Ti–Ni–Sn ternary alloys was investigated. Applying recent models based on atomic size ratio and efficient packing, the composition favoring the glass formation is predicted. Our experiments indicate that the optimized glass-forming composition is located at Ti₅₆Ni₃₈Sn₆, with the critical thickness of complete glass formation approaching 100 μm for the melt-spun ribbons. The Ti₅₆Ni₃₈Sn₆ metallic glass exhibits a sizable supercooled liquid region (ΔT_x) of about 35 K and a reduced glass transition temperature (T_rg) of 0.52. We demonstrate that the glass formation of the Ti₅₆Ni₃₈Sn₆ alloy correlates with the (L → TiNi + Ti₃Sn) pseudo binary eutectic reaction in Ti–Ni–Sn ternary system, which has an invariant temperature and composition at ～1370 K and ～Ti₅₈Ni₃₄Sn₈, respectively. With respect to Sn-free Ti–Ni binary alloys, the GFA is enhanced for the Ti–Ni–Sn ternary alloys, but the improvement is limited possibly due to changes in the crystalline phases competing with glass formation.     

Synthesis and characterization of M2O–MgO–WO3–P2O5 (M = K, Rb, Cs) glass system

Transparent glasses of the composition M₂O–MgO–WO₃–P₂O₅ (M = K, Rb, Cs), corresponding to the crystalline phases of M₂MgWO₂(PO₄)₂, have been prepared and studied by Raman and IR spectroscopy as well as DTA. Moreover, the thermally stimulated depolarization and dc conductivity have been measured. The glass transition temperature is 797, 795 and 773 K for the K-, Rb- and Cs-containing glass, respectively. Raman and IR studies have shown that these glasses have very similar structure. The main building blocks are pyrophosphate groups, WO₆ octahedra and magnesium–oxygen polyhedra. The dc conduction in these glasses is controlled by hopping of small polarons. The potassium containing glass was shown to be very stable whereas the rubidium and cesium glasses have significantly higher tendency for crystallization and phase separation. It seems, therefore, that the potassium containing glass is a suitable material for the preparation of samples containing non-linear and ferroelectric nanocrystals of the K₂MgWO₂(PO₄)₂ phosphate.     

Effects of hydration,annealing, and melting on heat transport properties of fused quartz and fused silica from laser-flash analysis

Thermal diffusivity (D) at high temperature (T) was measured from 15 samples of commercial SiO₂ glasses (types I, II, and III with varying hydroxyl contents) using laser-flash analysis (LFA) to isolate vibrational transport, in order to determine effects of impurities, annealing, and melting. As T increases, D_glass decreases, approaching a constant (~ 0.69 mm²s^? 1) above ~ 700 K. From ~ 1000 K to the glass transition, the slope of D is small but variable. Increases of D with T of up to 6% correlate with either low water and/or low fictive temperature and are attributed to removal of strain and defects during annealing. Upon crossing the glass transition, D substantially decreases to 0.46 mm²s^? 1 for the anhydrous melt. Hydration decreases D_glass, makes the glass transition occur over wider temperature intervals and at lower T, and promotes nucleation of cristobalite from supercooled melt. Due to the importance of thermal history, a spread in D of about 5% occurs for any given chemical type. Combining prior steady-state, cryogenic data with our average results on type I glass provides thermal conductivity (k_lat = ρC_PD) for type I: k_lat increases from ~ 0 K, becoming nearly constant above 1500 K, and drops by ~ 30% at T_g. We find that D^? 1(T) correlates with thermal expansivity times temperature from ~ 0 K to melting due to both properties arising from anharmonicity.     

Preparation of mixed arsenic/antimony chalcogenide glasses and some optical and thermo-physical properties

The preparation of mixed glasses of As₂S_3−xSe_x (x = 0–3) and (1 − y) · As₂S₃y · Sb₂S₃ (y = 0–1) has been carried out by an in situ pouring technique. X-ray diffraction (XRD) was used to confirm the glassy nature of the materials and monitor devitrification. Visible-IR transmission, photoluminescence, refractive index and micro-Raman were measured as a function of composition. Microhardness (MH) and thermal expansion coefficient (TEC) were also measured. Raman peaks in As₂S₃ and As₂Se₃ were observed around 338 cm⁻¹ and 230 cm⁻¹, respectively in this first composition series in which S was replaced by Se. When As was replaced by Sb, in the case of second composition series, the As₂S₃ related Raman peak became broader and shifted to lower wave number, reflecting some structural change/devitrification. MH increased (1.31–1.50 GPa) with Se and Sb content while the TEC was found to decrease (2.5–1.4 × 10⁻⁵/K). The progressive increase in the content of either Se or Sb in As₂S₃ is anticipated to modify bond lengths and bond angles. The combined effect of these structural modifications would change the local structure of the glass forming a more rigid glass network thereby increasing the hardness and decreasing TEC.     

Structural and optical spectroscopy of LiNbO3:Tm nanocrystals embedded in a SiO2 glass matrix

Transparent SiO₂:Li₂O:Nb₂O₅ glass doped with Tm³⁺ has been prepared by the sol–gel method, and heat-treated in air (HT) at temperatures between 500 and 800 °C. X-ray diffraction (XRD) patterns and Raman spectroscopy show SiO₂ and LiNbO₃ phases in samples HT above 650 °C, and a NbTmO₄ phase for T > 750 °C. The XRD SEM analysis show increasing particle size and number with the increase of HT temperature. Intra-4f¹² transitions due to Tm³⁺ ion dispersed in the matrix are observed in samples with T > 650 °C. The luminescence is dominated by the ¹G₄ → ³F₄ (～650 nm), ¹D₂ → ³F₃ (～780 nm), ³H₄ → ³H₆ (～800 nm), ³H₅ → ³H₆ (～1200 nm) and ³H₄ → ³F₄ (～1500 nm) transitions under resonant excitation to the ion levels.     

Photo-crystallization in a-Se imaging targets: Raman studies of competing effects

Photo-induced crystallization of a-Se is investigated by Raman spectroscopy as a function of temperature (250–340 K) and exposure time in thin-film structures used as targets in high-gain avalanche rushing photoconductor (HARP) video cameras. The Stokes-to-Antistokes ratio is monitored to obtain the local temperature T_loc at the laser spot; fluxes (632 nm) of 17 and 10 W/cm² are used. We find a rich temperature behavior that reflects the competition of changes in viscosity and strain, and defines four distinct regimes. No photo-crystallization is seen for T_loc below 260 K, nor in a 15 K range around T_g ～ 310 K. For T_loc in the regime 260–302 K the initial rate of crystal growth after onset of photo-crystallization is temperature independent, whereas for T_loc > 318 K the growth rate is thermally enhanced. Our results are in qualitative accord with a theory by Stephens treating the effects of local strain on the secondary growth of crystalline nuclei in a-Se. We conclude that the observed growth rate between 260 and 302 K is driven by local strain, and that relaxation of this strain near T_g suppresses crystal growth until thermally assisted processes accelerate the photo-crystallization at higher temperatures.     

A local structure change of bulk Pd40Ni40P20 glass during full relaxation

The change in the amorphous structure of bulk Pd₄₀Ni₄₀P₂₀ glass during structural relaxation was examined by an anomalous X-ray scattering (AXS) experiment with energies near the Ni K-absorption edge. It was confirmed by differential scanning calorimetry that the sample reached a meta-stable state (a fully relaxed state) with an equilibrium free volume concentration after annealing for about 1 × 10⁴ s at 563 K and 4 × 10⁴ s at 557 K just below the glass transition temperature T_g = 567 K. The structural changes on the progression toward a fully relaxed state were examined in samples annealed for 1 × 10³ and 2 × 10⁴ s at 563 K (glass A), and for 3.2 × 10³, 1 × 10⁴ and 7 × 10⁴ s at 557 K (glass B). The structural analysis revealed that the coordination number of Ni–Ni like atom pairs increased with annealing time and that of Ni–Pd, unlike atom pairs, decreased. Meanwhile, the coordination number N_PNi of P–Ni atom pairs and the nearest neighbor distance r_PNi did not show a remarkable variation. However, prolonged annealing of 7 × 10⁴ s at 557 K induced a remarkable change in N_PNi and r_PNi.     

Fast ion conducting phosphate glasses and glass ceramic composites: Promising materials for solid state batteries

Fast ion conducting (FIC) phosphate glasses and glass ceramic composites have gained considerable importance due to their potential applications in the fabrication of solid-state batteries and other electrochemical devices. We, therefore, present an overview on various types of FIC glasses and glass ceramic composites. Silver phosphate glasses doped with different weight percent of lithium chloride (1, 5, 10 and 15 wt.%) were synthesized by melt quenching technique. The Ag₂O–P₂O₅–(15 wt.%) LiCl glass exhibited the maximum electrical conductivity (σ = 8.91 × 10^? 5 S cm^? 1 at room temperature and 4.16 × 10^? 3 S cm^? 1 at 200 °C). Using this glass as an amorphous host material, glass–ceramic composites of Ag₂O–P₂O₅–(15 wt.%) LiCl:xAl₂O₃ (x = 5–50 wt.%) were prepared. The ionic transference number, electrical conductivity, ionic mobility and carrier ion concentration of the synthesized samples were measured. Ag₂O–P₂O₅–(15 wt.%) LiCl:(25 wt.%) Al₂O₃ composite system exhibited the maximum σ value (σ = 3.32 × 10^? 4 S cm^? 1 at room temperature and 2.88 × 10^? 2 S cm^? 1 at 200 °C ). Solid‐state batteries using undoped Ag₂O–P₂O₅ glass, Ag₂O–P₂O₅–(15 wt.%) LiCl glass and glass ceramic composite containing 25 wt.% Al₂O₃ as electrolytes were fabricated. The open circuit voltage (OCV) values and discharge time of these cells were measured and compared. It is found that the glass ceramic composites show enhanced ionic conduction, better OCV value and discharge characteristics.     

The origin of nanostructuring in potassium niobiosilicate glasses by Raman and FTIR spectroscopy

The structure of potassium niobium silicate glasses in a wide compositional range has been studied by means of Raman and FTIR spectroscopy. The glasses spectra were compared to those of the KNbSi₂O₇ and K₃Nb₃O₆Si₂O₇ polycrystalline samples, obtained by crystallization of glasses of the same composition. It was found that the structure of such glasses is formed by SiO₄ tetrahedra and distorted NbO₆ octahedra. The amount of highly distorted (edge-sharing, non-bridging oxygens) octahedra results essentially unchanged from the glass composition. By contrast, the fraction of octahedra with a lower distortion degree (corner-sharing, bridging oxygens) increases with the Nb₂O₅ content. Raman and FTIR investigations indicate that during long heat treatments at temperatures near T_g, in the 23K₂O · 27Nb₂O₅ · 50SiO₂ glass, a structural change occurs regarding the amorphous matrix with a decrease of the niobium octahedra distortion. This can be related to a segregation process producing niobium rich regions nanometric in size. In the first heat treatment (2 h) the glass remains amorphous while for more prolonged heat treatments, nanocrystals of an unidentified phase are formed. In the same time the changes of the amorphous matrix hinder further crystallization.     

Quantitation of sulfate solubility in borosilicate glasses using Raman spectroscopy

Raman spectroscopy is used here as an innovative technique to investigate sulfate content in borosilicate glasses. Using Raman spectroscopy after having heated the material, the evolution of sulfate amounts can be followed as a function of temperature, time and chemical composition of the starting matrix. The accuracy of this technique was verified using electron probe micro analysis (EPMA), on two systems of glasses (SiO₂–B₂O₃–Na₂O (SBNa) and SiO₂–B₂O₃–BaO (SBBa)) in order to compare the effect of alkaline or alkaline-earth elements on sulfur speciation and incorporation. To quantitate sulfate content with Raman spectroscopy, the integrated intensity of the sulfate band at 990 cm^?1 was scaled to the sum of the integrated bands between 850 and 1250 cm^?1, bands that are assigned to Qⁿ silica units. Calibration curves were then determined for different samples. The determination of sulfate contents with Raman spectroscopy analysis is possible with an accuracy of approximately 0.1 wt% depending on the composition of the glass. It mainly allows us to follow sulfate removal during the elaboration process and to establish kinetic curves of sulfate release as a function of the viscosity of the borosilicate glass.     

Structure and properties of MoO3-containing zinc borophosphate glasses

ZnO–B₂O₃–P₂O₅ glasses doped with MoO₃ were investigated in the series (100?x)[0.5ZnO–0.1B₂O₃–0.4P₂O₅]–xMoO₃, where bulk glasses were obtained by slow cooling in air within the compositional region of 0 ? x ? 60 mol% MoO₃. The incorporation of MoO₃ into the parent zinc borophosphate glass results in a weakening of bond strength in the structural network, which induces a decrease in chemical durability and glass transition temperature. Raman spectra reflect the incorporation of molybdate groups into the glass network of the studied glasses by the presence of the polarized vibrational band at ≈976 cm^?1 ascribed to the MO_x symmetric stretching vibrations and the depolarized band at ≈878 cm^?1 ascribed to the Mo–O–Mo stretching vibration. The incorporation of molybdate units into the glass network results in the depolymerization of phosphate chains and the formation of P–O–Mo bonds, as reflected in Raman and ³¹P NMR spectra. According to the ¹¹B MAS NMR spectra, tetrahedral B(OP)_4?x(OMo)_x units are formed in the glasses, whereas only a small amount of BO₄ units is converted to BO₃ units in the MoO₃-rich glasses.     

Structure and properties of potassium niobato-borophosphate glasses

Bulk glasses of the series (1 ? x)[0.5K₂O–0.1B₂O₃–0.4P₂O₅]–xNb₂O₅ with x = 0–45.7 mol% Nb₂O₅ were prepared by slow cooling in air and investigated by Raman, ³¹P, and ¹¹B MAS NMR spectroscopy. The incorporation of Nb₂O₅ into the parent borophosphate glass results in a substantial increase in the glass transition temperature and chemical durability of glasses. Raman spectra showed that Nb atoms form distorted NbO₆ octahedra, which are isolated at low Nb₂O₅ content, whereas at higher Nb₂O₅ content they form clusters. ¹¹B NMR spectra of the glasses revealed the interaction between Nb₂O₅ and BO₄ tetrahedral units, which results in a partial transformation of tetrahedral BO₄ units to trigonal BO₃ units and the formation of mixed B(OP)_4?n(ONb)_n units.     

Heterophase inclusions and dissolved impurities in Ge25Sb10S65 glass

The impurity content and microhomogeneity of Ge₂₅Sb₁₀S₆₅ glass samples, prepared by direct synthesis from elements, were investigated. It was shown that the increase in temperature of synthesis of the glass-forming melt resulted in the increase of the content of impurities of H, Na, Al, Si, K, Ca and transition metals in the prepared glasses. The glasses from the melt, subjected to chemical-distillation purification, were characterized by the low content of gas-forming impurities and the increased content of Al, Si and Cl. The glasses contained heterophase impurity inclusions mainly consisting of SiO₂, and their concentration and size depended on the conditions of glass preparation. The impurity content in the purest glasses was as follows: oxygen – <0.5 ppm wt, carbon – <5 ppm wt, hydrogen – 0.1 ppm wt, Si – <1 ppm wt, transition metals – <0.25 ppm wt, heterophase impurity inclusions with sizes larger than 80 nm – <10² cm³. It was shown that heterophase impurity inclusions behaved as the centers of glass crystallization.     

Effect of OH-content on thermal and chemical properties of SnOP2O5 glasses

Glasses with 55–60 mol% SnO and 40–45 mol% P₂O₅ have shown extremely large differences in the chemical and thermal properties depending on the temperature at which they were melted. Glasses prepared at low melting temperature, 450–550 °C, had low T_g, 150–200 °C, and low chemical stability. Glasses prepared at high melting temperature, 800–1200 °C, had much higher T_g, 250–300 °C, and much higher chemical stability. No significant differences were found by ¹¹⁹Sn Mössbauer and ³¹P Nuclear Magnetic Resonance spectroscopy. Large differences in the OH-content could be detected as the reason by infrared absorption spectroscopy, thermal analyses, and ¹H Nuclear Magnetic Resonance spectroscopy. In samples with low T_g, a broad OH – vibration band around 3000 nm with an absorption intensity >20 cm^?1, bands at 2140 nm with intensity ～5 cm^?1, at 2038 nm with intensity ～2.7 cm^?1, and at 1564 nm with intensity ～0.4 cm^?1 were measured. These samples have shown a mass loss of 3–4 wt% by thermal gravimetric analyses under argon in the temperature range 400–1000 °C. No mass loss and only one broad OH-band with a maximum at 3150 nm and low absorption intensity <4 cm^?1 could be detected in samples melted at high temperature, 1000–1200 °C, which have much higher T_g, ～300 °C, and much higher chemical stability.