Glass formation, physico-chemical properties, and structure of glasses based on Ga2S3-GeS2-Sb2S3 system

We prepared sulfide glasses based on a Ga₂S₃-GeS₂-Sb₂S₃ system and investigated the compositional dependences of their physico-chemical properties and structure. Additivities were observed for density and refractive index; i.e., these properties were presented by the summation of the contribution from each component. With the increase of Sb₂S₃ content, the density, refractive index, and thermal expansion coefficient increased while the glass transition and softening temperatures decreased, and the short-wavelength absorption edge shifted to the longer wavelength side. These variations are expected from the incorporation of a heavy element (Sb) into the glasses. On the other hand, the replacement of GeS₂ by Ga₂S₃ increased the density and refractive index, and shifted the short-wavelength absorption edge to the longer wavelength side. These variations were explained by the increase of the number densities of the cations with the replacement and the formation of metal-metal bonds. The latter was confirmed from the Raman spectra. We also investigated the effects of Ag₂S incorporation on the optical properties. The incorporation of Ag₂S increased the density and refractive index whereas the position of the short-wavelength absorption edge varied little. These results show the possibility of fabricating an optical waveguide by Ag incorporation into the glasses.     

Synthesis and physical properties of glasses in the Sb2O3-PbCl2-MoO3 system

Lead chloroantimonite glasses form stable binary glasses that may accommodate numerous oxides or halides as a third component. Molybdenum trioxide is a glass progenitor leading to molybdate glasses. Ternary glasses have been synthesized and studied in the Sb₂O₃-PbCl₂-MoO₃ system. Compositional limits of glass formation are reported and two series of glass samples have been prepared corresponding to the general formulas: (90 − x)Sb₂O₃-xPbCl₂-10MoO₃ and (90 − x)Sb₂O₃-xMoO₃-10PbCl₂. Glass transition temperature is close to 290 °C at high Sb₂O₃ content and decreases as antimony oxide is substituted by MoO₃ or PbCl₂. Position, width and intensity of crystallization peak suggest that devitrification rate is small in some composition ranges. The evolution of density, thermal expansion, refractive index and microhardness has been studied as a function of composition parameter x. Deviations from linearity are observed. They suggest structural changes in the case of the MoO₃/Sb₂O₃ substitution while it appears that molar volume increases linearly versus lead content in the other series of glasses. Refractive index is close to 2.04. Optical transmission ranges from 550 nm in the visible spectrum to 5.5 μm in the infrared. It is limited by extrinsic absorption bands arising from hydroxyls and silicon impurities. Young's, bulk and shear moduli have been measured for the two series of samples.     

The comparative structure, properties, and ionic conductivity of LiI + Li2S + GeS2 glasses doped with Ga2S3 and La2S3

The well known and characterized fast ion conducting (FIC) LiI + Li₂S + GeS₂ glass-forming system has been further optimized for higher ionic conductivity and improved thermal and chemical stability required for next generation solid electrolyte applications by doping with Ga₂S₃ and La₂S₃. These trivalent dopants are expected to eliminate terminal and non-bridging sulfur (NBS) anions thereby increasing the network connectivity while at the same time increasing the Li⁺ ion conductivity by creating lower basicity [(Ga or La)S_4/2]⁻ anion sites. Consistent with the finding that the glass-forming range for the Ga₂S₃ doped compositions is larger than that for the La₂S₃ compositions, the addition of Ga₂S₃ is found to eliminate NBS units to create bridging sulfur (BS) units that not only gives an improvement to the thermal stability, but also maintains and in some cases increases the ionic conductivity. The compositions with the highest Ga₂S₃ content showed the highest T_gs of ∼325 °C. The addition of La₂S₃ to the base glasses, by comparison, is found to create NBS by forming high coordination octahedral LaS₆³⁻ sites, but yet still improved the chemical stability of the glass in dry air and retained its high ionic conductivity and thermal stability. Significantly, at comparable concentrations of Li₂S and Ga₂S₃ or La₂S₃, the La₂S₃-doped glasses showed the higher conductivities. The addition of the LiI to the glass compositions not only improved the glass-forming ability of the compositions, but also increased the ionic conductivity glasses. LiI concentrations from 0 to 40 mol% improved the conductivities of the Ga₂S₃ glasses from ∼10⁻⁵ to ∼10⁻³ (Ω cm)⁻¹ and of the La₂S₃ glasses from ∼10⁻⁴ to ∼10⁻³ (Ω cm)⁻¹ at room temperature. A maximum conductivity of ∼10⁻³ (Ω cm)⁻¹ at room temperature was observed for all of the glasses and this value is comparable to some of the best Li ion conductors in a sulfide glass system. Yet these new compositions are markedly more thermally and chemically stable than most Li⁺ ion conducting sulfide glasses. LiI additions decreased the T_gs and T_cs of the glasses, but increased the stability towards crystallization (T_c − T_g).     

Compositional dependence of the optical gap in Ge1−xSx, Ge40−xSbxS60 and (As2S3)x(Sb2S3)1−x non-crystalline systems

An attempt is made to calculate the compositional dependence of the optical gap (E_g) in Ge_1−xS_x, Ge_40−xSb_xS₆₀ and (As₂S₃)_x(Sb₂S₃)_1−x non-crystalline systems in an alloy-like approach. From the comparison of both the experimental dependence of E_g and the calculated ones using the Shimakawa relation [E_{g AB} = YE_{g A} + (1−Y)E_{g B}] it is assumed that this equation is useful for such systems or parts of the systems which behave like almost ideal solutions.     

Structural analysis and devitrification of glasses based on the CaO-MgO-SiO2 system with B2O3, Na2O, CaF2 and P2O5 additives

Glasses, whose basic composition was based on the CaO-MgO-SiO₂ system and doped with B₂O₃, P₂O₅, Na₂O, and CaF₂, were prepared by melting at 1400 °C for 1 h. Raman and infrared (IR) spectroscopy revealed that the main structural units in the glass network were predominantly Q¹ and Q² silicate species. The presence of phosphate and borate units in the structure of the glasses was also evident in these spectra. X-ray analysis showed that the investigated glasses devitrified at 750 °C and higher temperatures. The crystalline phases of diopside and wollastonite dominated, but weak peaks, assigned to akermanite and fluorapatite, were also registered in the diffractograms. The presence of B₂O₃, Na₂O, and CaF₂ had a negligible influence on the assemblage of the crystallized phases, but it caused a reduction of crystallization temperature, comparing to similar glasses of the CaO-MgO-SiO₂ system.     

Preparation and characterization of glasses in the Ag2S + B2S3 + GeS2 system

The glass forming range of the Ag₂S + B₂S₃ + GeS₂ ternary system was investigated for the first time and a wide range of ternary glasses were obtained. The Archimedes’ method was used to determine the densities of the Ag-B-Ge glasses. The thermal properties of these thioborogermanate glasses were studied by DSC and TMA. The Raman, IR and NMR spectroscopy were used to explore the short-range order structure of the binary (Ag-B) and (Ag-Ge) and ternary (Ag-B-Ge) glasses. The results show the presence of bridging sulfur tetrahedral units, GeS_4/2 and AgBS_4/2, and trigonal units, BS_3/2, in the ternary glasses. Non-bridging sulfur units, AgSGeS_3/2 and Ag₃B₃S₃S_3/2 six membered rings, are also observed in these glasses at higher Ag₂S modification levels because the further addition of Ag₂S results in the degradation of the bridging structures to form non-bridging structures. The NMR studies show that Ag₂S goes into the GeS₂ subnetwork to form Ag₃S₃GeS_1/2 groups before going to the B₂S₃ subnetwork. In doing so, it is suggested that B₁₀S₂₀ supertetrahedra exist in Ag₂S + B₂S₃ and Ag₂S + B₂S₃ + GeS₂ glasses. Significantly B-S-Ge bonds form in the B₂S₃ + GeS₂ glasses, whereas they appear to be absent in the ternary glasses. From these observations, a structural model for these glasses has been developed and proposed.     

Effect of Bi2O3 proportion on physical, structural and electrical properties of zinc bismuth phosphate glasses

The variation in physical, structural and electrical properties has been studied as a function of Bi₂O₃ content in 20ZnF₂-(10 + x) Bi₂O₃-(70-x) P₂O₅, 0 ≤ x ≤ 10 mol% glasses, which were prepared by melt quenching technique and characterized by differential thermal analysis (DTA). Colorless samples, which have no absorption peaks, are obtained for 10 and 12 mol% of Bi₂O₃ and the glasses are slowly becoming brownish from 15 to 20 mol% of Bi₂O₃ which exhibit two absorption peaks at ~ 370 nm, ~ 450 nm correspond to Bi° transitions ⁴S_3/2 → ²P_3/2 and ⁴S_3/2 → ²P_1/2 respectively. The decrease in ³P₁ → ¹S₀ transition of Bi³⁺ photo luminescence emission for 18 and 20 mol% of Bi₂O₃ and increase in optical absorption area shows the reduction of Bi³⁺ to Bi°. From FTIR studies it is observed that an addition of Bi₂O₃ decreases the P―O―P covalent bond by forming P―O―Bi bonds due to high polarizing nature of Bi³⁺ ions. Dielectric parameters like ε', tan δ and a.c. conductivity σ_ac are found to increase and activation energy for a.c. conduction is found to decrease with the increase in the concentration of Bi₂O₃. Density of defect energy states is found to increase for higher concentration of Bi₂O₃ and is discussed according to quantum mechanical tunneling (QMT) model.     

Laser-induced crystallization of β′-RE2(MoO4)3 ferroelectrics (RE: Sm, Gd, Dy) in glasses and their surface morphologies

The glasses with the compositions of 21.25RE₂O₃-63.75MoO₃-15B₂O₃ (RE: Sm, Gd, Dy) were prepared and the formation of β′-RE₂(MoO₄)₃ ferroelectrics was confirmed in the crystallized glasses obtained through a conventional crystallization in an electric furnace. The features of the glass structure and crystallization behavior were clarified from measurements of Raman scattering spectra. Continuous-wave Nd:YAG laser with a wavelength of 1064 nm (laser power: 0.6-0.9 W, laser scanning speed: S = 1-16 μm/s) was irradiated to 10.625Sm₂O₃-10.625Gd₂O₃ (or Dy₂O₃)-63.75MoO₃-15B₂O₃ glasses, and the structural modification was induced at the glass surface. At the scanning speed of S = 10 μm/s, crystal lines consisting of β′-Gd_2−xSm_x(MoO₄)₃ or β′-Dy_2−xSm_x(MoO₄)₃ crystals were patterned on the glass surface. It was found that those crystal lines have the surface morphology with periodic bumps. At S = 1 μm/s, it was found that crystal lines consist of the mixture of paraelectric α-Gd_2−xSm_x(MoO₄)₃ and ferroelectric β′-Gd_2−xSm_x(MoO₄)₃ crystals, indicating the phase transformation from the β′ phase to the α phase during laser irradiation. Homogeneous crystal lines with β′-RE₂(MoO₄)₃ ferroelectrics have not been written in this study, but further research is continuing.     

Electrical transport properties of 0.5Li2O-0.5M2O-2B2O3 (M = Li, Na and K) glasses

Transparent glasses in the system 0.5Li₂O-0.5M₂O-2B₂O₃ (M = Li, Na and K) were fabricated via the conventional melt quenching technique. The amorphous and glassy nature of the samples was confirmed via the X-ray powder diffraction and the differential scanning calorimetry, respectively. The frequency and temperature dependent characteristics of the dielectric relaxation and the electrical conductivity were investigated in the 100 Hz-10 MHz frequency range. The imaginary part of the electric modulus spectra was modeled using an approximate solution of Kohrausch-Williams-Watts relation. The stretching exponent, β, was found to be temperature independent for 0.5Li₂O-0.5Na₂O-2B₂O₃ (LNBO) glasses. The activation energy associated with DC conduction was found to be higher (1.25 eV) for 0.5Li₂O-0.5K₂O-2B₂O₃ (LKBO) glasses than that of the other glass systems under study. This is attributed to the mixed cation effect.     

Structure and properties of glasses in the MI + M2S + (0.1Ga2S3 + 0.9GeS2), M = Li, Na, K and Cs, system

The structure and properties of glasses in the MI + M₂S + (0.1Ga₂S₃ + 0.9GeS₂), M = Li, Na, K and Cs, system were studied using Raman, IR spectroscopy, DSC and density measurements to help better understand the ionic transport in these glasses. The glass forming ranges of these ternary glasses were compared to those of the binary alkali sulfide and germanium sulfide systems. The more extensive glass forming range in the Na₂S system was used to examine the more extensive changes of structure and properties of these glasses as a function of Na₂S content. As expected, non-bridging sulfurs (NBS) form with the addition of alkali sulfide. Unlike their oxide counterparts, however, the alkali sulfide doped glasses appear to support longer-range super-structural units. For example, evidence that the adamantine-like structure exists in the K₂S and Cs₂S modified glasses is found in the Raman spectra of the glasses. The structural role of the alkali iodide addition was also explored since the addition of alkali iodide helps to improve the conductivity. For most of these glasses, as observed in many other oxide glasses, the added MI dissolves interstitially into the glass structure network without changing the alkali sulfide network structure. In 0.6Na₂S + 0.4(0.1Ga₂S₃ + 0.9GeS₂) glasses, however, the added NaI may affect the glass structure as it causes systematic changes in the frequency of the Ge-S network mode as seen in the Raman spectra.     

Vibrational, EPR and optical spectroscopy of the Cu doped glasses with (90-x)TeO2-10GeO2-xWO3 (7.5 ≤ x ≤ 30) composition

Infrared, EPR and optical absorption studies on (90-x)TeO₂-10GeO₂-xWO₃ (7.5 ≤ x ≤ 30) glasses containing Cu²⁺ spin probe have been carried out. The Infrared spectral studies show that the structure of glass network consists of [TeO₄], [TeO₃]/[TeO_3 + 1], [WO₄], [WO₆] and [GeO₆] units in the disordered manner. Physical parameters such as density (ρ), molar volume (V_m), oxygen packing density (OPD), oxygen molar volume (V_o), optical basicity (Λ), oxide ion polarizability (α_O²⁻), inter ionic distances and the concentration of ions per unit volume of Te, Ge, W, Cu and O have been determined. The spin-Hamiltonian parameters (g_||, g_⊥ and A_||) of Cu²⁺ ions in the present glasses have been estimated from EPR spectra at 300 K. Bonding parameters such as α², β₁², β², Γ_σ, and Γ_π have been calculated from both optical absorption and EPR data. The observed variations in spin-Hamiltonian parameters and bonding parameters have been correlated to the structural modifications due to the WO₃ incorporation into the TeO₂ glass network at constant 10 mol% GeO₂ content.