Properties and structure of copper ultraphosphate glasses

The structures of xCuO · (1 − x)P₂O₅ glasses (0 ? x ? 0.50) prepared in vacuum sealed silica ampoules were investigated using vibrational spectroscopies. With the addition of CuO, both infrared and Raman spectra indicate a systematic transformation from a three-dimensional ultraphosphate network dominated by Q³ tetrahedra into a chain-like metaphosphate structure dominated by Q² tetrahedra. IR spectra clearly show two distinct Q³ sites with bands at 1378 and 1306 cm⁻¹, assigned to PO bonds on isolated Q³ tetrahedra and PO bonds on tetrahedra that participate in the coordination environments of the Cu-octahedra, respectively. As CuO content increases, the intensity of the PO band associated with the tetrahedra increases to a maximum x ∼ 0.33, then decreases with a concomitant increase of the intensity of the band at 1265 cm⁻¹, due to the asymmetric vibration of the PO₂ groups on Q² tetrahedra. When x > 0.33 the isolated Cu-octahedra begin to share common oxygens to form a sub-network in the phosphate matrix. The effects of glass structure on the glass properties, including density, refractive index, and glass transition temperature, are discussed.     

Interrelation between the parameters of equations of viscous flow and chemical composition of glassforming melts

The number of free parameters of viscosity equations are reduced to two by assuming that the glass transition temperature T_g is the temperature at which viscosity is 10^13.5 [dPa s]. In this way the Avramov and Milchev AM equation is becoming while the VFT equation is transformed to the form: . It is demonstrated that the dimensionless fragility parameter a of the AM equation depends on composition, x, as α = α_ο + 6x, where α_ο = 1 − 2 for silicates and α_ο = 2.75 for borates. We show that the fitting parameters of AM and of VFT equations are correlated. Thus the relationship between the pre-exponential constants is lg η_V ≈ lg η_A − 2. There is also relationship between the fragility parameter a and the divergence temperature T_o of the VFT equation.We develop an alternative approach to consider the vibration frequency of building units of the system. The superposition of the independent vibrations of the atoms constituting the building unit causes a “beat” of the latter.     

Glass transition and fragility of Na2O-TeO2 glasses

The heat capacity (C_p) change in the glass transition region for the xNa₂O ·(100−x)TeO₂, mol%, glass forming melts with x=7.5, 11.1, 15.0, 20.0 and 25.0 was measured as a function of heating rate (2, 4, 6, 10 and 15 °C/min) using differential scanning calorimetry. The glass transition properties that have been measured and reported in this paper include the glass transition temperature (T_g), glass transition width (ΔT_g), heat capacities in the glassy and liquid state (C_pg and C_pl) and the activation enthalpy for glass transition (). T_g for these sodium tellurite melts decreased and increased with increasing Na₂O. Values of the ratio C_pl/C_pg ranged between 1.28 and 2.47, and the fragility parameter ranged between 100 and 130, suggesting that these glass forming melts may be classified as intermediate between typical strong and fragile liquids. The viscosity, η, calculated at a few selected temperatures near the glass transition region decreased with increasing Na₂O at any given temperature, which is also expected.     

The glass transition temperature versus the fictive temperature

A comparison of the values of the glass transition temperature (T_g) measured on cooling and the limiting fictive temperature measured on heating as a function of cooling rate is performed for a polystyrene sample using both capillary dilatometry and differential scanning calorimetry (DSC). The results from both techniques indicate that is systematically lower than T_g presumably due to the breadth of the relaxation on cooling. The Tool-Narayanaswamy-Moynihan (TNM) model is used to fit the experimental data from dilatometry and DSC in order to ascertain the origins of the higher value of T_g compared to .     

The fabrication and properties of solid polymer electrolytes based on PEO/PVP blends

New solid polymer electrolytes were fabricated by the addition of lithium perchlorates in the blends of polyethylene oxide (PEO, MW = 5 × 10⁶) and poly-4-vinylpyridine (PVP, MW = 1.6 × 10⁶). Not only the coordinating bonding between ether units (-O-) of PEO and Li⁺ ions at about 1100 cm⁻¹ but also the existence of pyridine salts at about 3500 cm⁻¹ were definitely observed in the FT-IR spectra. The addition of PVP in the PEO matrix is to restrict mobility of ions through the coupling of PVP and ions. Therefore, the increase of PVP content is expected to decrease the self-discharge rate. In the case of PEO-PVP blends without LiClO₄, the melting temperature T_m and the degree of crystallinity were decreased by the increase of PVP content. On the contrary, those of PEO-PVP blends with LiClO₄ were increased with the increase of PVP content. The results can be explained lay ions, which reduced the crystallinity of PEO by steric hindrance, segregated from the PEO by the coupling of PVP and ions. The new solid polymer electrolytes based on PEO-PVP blends showed ionic conductivities of the order of 10⁻⁸ to 10⁻⁷ S/cm.     

A combined measurement of thermal and mechanical relaxation

In order to describe relaxation the thermodynamic coefficient can be generalized into a complex frequency-dependent cross response function. We explore theoretically the possibility of measuring for a supercooled liquid near the glass transition. This is done by placing a thermistor in the middle of the liquid which itself is contained in a spherical piezoelectric shell. The piezoelectric voltage response to a thermal power generated in the thermistor is found to be proportional to but factors pertaining to heat diffusion and adiabatic compressibility κ_S(ω) do also intervene. We estimate a measurable piezoelectric voltage of 1 mV to be generated at 1 Hz for a heating power of 0.3 mW. Together with κ_S(ω) and the longitudinal specific heat c_l(ω) which may also be found in the same setup a complete triple of thermoviscoelastic response functions may be determined when supplemented with shear modulus data.     

Structural investigation of sodium borate glasses and melts by Raman spectroscopy. II. Conversion between BO4 and BO2O units at high temperature

Raman scattering spectra were recorded for pure boron oxide and sodium borate glasses and their melts at the temperature ranging from room temperature to 1200 °C to investigate the structural changes occurring in the melts. The amounts of short-range order structures (SRO), BO₂O⁻ and BO₃, were estimated from the high frequency bands at 1100-1600 cm⁻¹. The ratio of 4-fold coordinated boron oxide BO₄, N₄, at high temperature could be derived for the glass melts as a function of Na₂O concentration. In Na₂O ?20 mol% region, N₄ showed a slight decrease while the remarkable decrease of N₄ was found in the region of Na₂O ?25 mol% with increasing temperature. The enthalpy of the equilibrium reaction,

     

Formation of complex structural units and structure of some chalco-halide glasses

Raman spectra, thermal expansion and glass transition temperature of glasses and evolution of Raman spectra of CsGaS_1.5Cl glasses with complete substitution of S by Se and partial substitution of Ga by Al (or In) and of Cl by Br (or I) were studied. The structure of these glasses was discussed considering the ability of A(III) metals to form complex tetrahedral structural units [A(III)B(VI or VII)₄]¹⁻, which can be connected by sharing either the common corner of tetrahedra (glasses of systems at x>0.1 and CsInS_1.5Cl glass) or the common edge of tetrahedra (CsGaS_1.5Cl, CsAlS_1.5Cl, CsGaSe_1.5Cl, CsGaS_1.5Br, CsGaS_1.5I glasses).     

A sharp thermally reversing window in As45Te55−xIx chalcohalide glasses revealed by alternating differential scanning calorimetry and photo thermal deflection studies

The composition dependence of different thermal parameters such as glass transition temperature, non-reversing enthalpy, thermal diffusivity etc., of bulk As₄₅Te_55−xI_x chalcohalide glasses (3 ? x ? 10), has been evaluated using the temperature modulated Alternating Differential Scanning Calorimetry (ADSC) and Photo Thermal Deflection (PTD) studies. It is found that there is not much variation in the glass transition temperature of As₄₅Te_55−xI_x glasses, even though there is a wide variation in the average coordination number . This observation has been understood on the basis that the variation in glass transition temperature of network glasses is dictated by the variation in average bond energy rather than . Further, it is found that both the non-reversing enthalpy (ΔH_nr) and the thermal diffusivity (α) exhibit a sharp minimum at a composition x = 6. A broad hump is also seen in glass transition and crystallization temperatures in the composition range 5 ? x ? 7. The results obtained clearly indicate a sharp thermally reversing window in As₄₅Te_55−xI_x chalcohalide glasses around the composition x = 6.     

Growth, thermal and spectral properties of Nd-doped NaGd(MoO4)2 crystal

Nd³⁺-doped NaGd(MoO₄)₂ crystal with dimensions were grown by Czochralski method. Nd³⁺:NaGd(MoO₄)₂ crystal melts at 1182 °C. The hardness of Nd³⁺:NaGd(MoO₄)₂ crystal is 334 VDH. The specific heat is 72.6 cal/mol K. The thermal expansion coefficients are for c-axis and for a-axis, respectively. The absorption cross-sections of Nd³⁺:NaGd(MoO₄)₂ crystal are with a FWHM of 9 nm at the 804 nm for π-polarization and with a FWHM of 17 nm at 807 nm for σ-polarization, respectively. The emission cross-section σ_em are at 1063 nm for π-polarization and 1.94×10^-20 at 1070 nm cm² for σ-polarization, respectively. The fluorescence lifetime τ_f is 93.9 μs at room temperature.