Characterization of chitosan/PVA blended electrolyte doped with NH4I

The (chitosan–PVA)–NH₄I electrolytes have been prepared by the solution casting method. The prepared electrolytes are analyzed using Fourier transform infrared (FTIR) spectroscopy in order to determine the interaction between salt and the polymer blend hosts which can be deduced from the band shifting. From infrared spectra, shifts are observed at the amine, carboxamide, carbonyl and hydroxyl bands of chitosan and PVA. These shifts indicate that complexation has occurred. The crystallinity/amorphousness of the blended electrolytes has been examined by X-ray diffraction (XRD). XRD pattern shows that the crystallinity of chitosan–NH₄I electrolyte increases with PVA concentration. Impedance of the electrolytes has been measured using electrochemical impedance spectroscopy (EIS) over the frequency range from 50 Hz to 1 MHz. The highest conducting sample 55 wt.% (chitosan–PVA)–45 wt.% NH₄I has conductivity of 1.77 × 10^? 6 S cm^? 1. The chitosan:PVA ratio is 1:1. This is higher than the conductivity for the unblended electrolyte 55 wt.% chitosan–45 wt.% NH₄I which is 3.73 × 10^? 7 S cm^? 1. From ln τ versus 10³/T plot, the activation energy for relaxation process is 0.87 eV. This is different from activation energy for dc conductivity which is 0.38 eV. Ion conduction is by hopping.     

Exploration on nano-composite fumed silica-based composite polymer electrolytes with doping of ionic liquid

Fumed silica (SiO₂)-based composite polymer electrolytes were prepared by means of solution casing technique. Horizontal attenuated total reflectance-Fourier Transform Infrared (HATR-FTIR) study shows the complexation between polymer matrix and SiO₂. The highest ionic conductivity of (4.11 ± 0.01) × 10^? 3 Scm^? 1 is achieved upon inclusion of 8 wt.% of SiO₂. Three different regions have been observed in the frequency dependence–ionic conductivity study. The conductivity rises sharply with frequency at low frequency regime. It is followed by a frequency independent plateau region and sharp decrease in the conductivity at high frequency range. The dielectric permittivity (ε^') and dielectric loss (ε^") are decreased with increasing the frequency. This phenomenon is mainly attributed to the electrode polarization effect. The formation of electrical double layer has been proven in these dielectric permittivity studies. This indicates the non-Debye properties of the nano-composite polymer electrolytes.     

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.     

Synthesis and thermal characterization of glass bonded Ca-chloroapatite matrices for pyrochemical chloride waste immobilization

Ca-chloroapatite (CaApCl), glass-bonded CaApCl compositions loaded with 16–32 wt.% simulated pyrochemical chloride waste were prepared by mixing and heating (773–1023 K) apatite and borosilicate glass (BSG) forming reagents in appropriate ratios. The compositions were characterized by XRD, TGA/DTA, SEM, and EDAX. Among the products, 16–27 wt.% chloride waste loaded composition yielded phase pure Ca-chloroapatite and were resistant to leaching of Cl^? and other ions. In case of 28–32 wt.% waste loaded compositions, even though formation of phase pure Ca-Chloroapatites was observed by XRD, the leaching of Cl^? and other ions was found to be significant. Bulk thermal expansion behavior of the samples was studied by dilatometry. The 16 wt.% chloride waste loaded matrix showed nearly the same thermal expansion compared to pure Ca-Chloroapatites. The % linear thermal expansion of the matrices decrease on increasing the chloride waste loading; however, Ca-chloroapatite mixed with 20 wt.% BSG mixed matrix showed slightly higher thermal expansion. The coefficient of thermal expansion of borosilicate glass is the lowest among all the matrices measured. The coefficient of thermal expansion (CTE) is found to be 12.76 ± 0.64 × 10^? 6 K^? 1 for CaApl and 12.18 ± 0.63 × 10^? 6 K^? 1 for 16 wt.% waste loaded BSG-encapsulated CaApl in the temperature range of 298–780 K. The glass transition temperature of the waste loaded matrices is lower than that of the bare BSG and 20 wt.% BSG encapsulated Ca-chloroapatite.     

Preparation of super hydrophobic silica aerogel and study on its fractal structure

The experimental results on silica aerogels with super hydrophobic property are reported. Silica alcogels were prepared via a two-step acid/base process by keeping the molar ratio of tetraethyoxysiliane (TEOS), ethanol (EtOH), water (H₂O), hydrochloric acid (HCl) and ammonia (NH₄OH) constant at 1:6:8:1.0 × 10^?3:1.1 × 10^?2, respectively, and varying the molar ratio of N,N-dimethylformamide (DMF)/TEOS (G) from 0 to 1.2. After two aging treatment steps, they were modified by isopropyl alcohol (IPA)/trimethylchlorosilane (TMCS)/n-hexane solution at 60 °C. It was found that G value at 0.8 resulted in low density (～0.2 g cm^?3) and the minimum volume shrinkage (～6%), with the total water adsorption ratio ～5.1% when exposed to water for 3 months and the contact angle θ ≈ 178°. Besides, the aerogels (G = 0.8) had higher volume fractal dimension (～1.8), which indicted that it possessed better connectivity and more uniform particle sizes.     

ac conductivity in a-Ge–Se–Bi glasses

In the present paper the effect of Bi impurity (low ∼4 at.% and high ∼10 at.%) on the ac conductivity (σ_ac) of a-Ge₂₀Se₈₀ glassy alloy is studied and the experimentally deduced values are fitted with theoretically deduced values by using correlated barrier hopping model (CBH). Frequency dependent ac conductance of the samples over a frequency range of 100–50 kHz has been taken in the temperature range (268–360 K). At frequency 2 kHz and temperature 298 K, the value of ac conductivity (σ_ac) decreases at low concentration of Bi (4 at.%). However, the value of σ_ac increases at higher concentration of Bi (10 at.%). The ac conductivity is proportional to ω^s for undoped and doped samples. The value of frequency exponent (s) decreases as the temperature increases. These results have been explained on the basis of some structural changes at low and high concentration of Bi impurity.     

Growth of CdSiP2 single crystals by self-seeding vertical Bridgman method

Using a high purity CdSiP₂ polycrystalline charge synthesized in a single-temperature zone furnace, a CdSiP₂ single crystal with dimensions of 8 mm in diameter and 40 mm in length was successfully grown by the vertical Bridgman method. The quality of the crystal was characterized by high resolution X-ray diffraction and the full width at half maximum (FWHM) of the rocking curve for the (200) face is 33″. Thermal property measurements show that: the mean specific heat of CdSiP₂ between 300 and 773 K is 0.476 J g^?1 K^?1; the thermal conductivity of the crystal along the a- and c-axes is 13.6 W m^?1 K^?1 and 13.7 W m^?1 K^?1 at 295 K, respectively; and the thermal expansion coefficient measured along the a- and c-axes is 8.4×10^?6 K^?1 and ?2.4×10^?6 K^?1, respectively. The optical transparency range of the crystal is 578–10,000 nm, and there is no absorption loss in the spectrum from 0.7 to 2.5 μm, as often exists with ZnGeP₂ crystals grown from the melt.     

Alkaline earth zinc borate glasses doped with Cu2+ ions studied by EPR,optical and IR techniques

Copper ions incorporated into alkaline earth zinc borate glasses 10RO + 30ZnO + 60B₂O₃ (R = Mg, Ca and Sr) and 10SrO + (30 ? x)ZnO + 60B₂O₃ + xCuO (x = 0, 0.1, 0.3, 0.5, and 0.7 wt.%) were characterized by electron paramagnetic resonance (EPR), optical absorption and FTIR techniques. The EPR spectra of all the glass samples exhibit resonance signals characteristic of Cu²⁺ ions. The values of spin-Hamiltonian parameters indicate that the Cu²⁺ ions in alkaline earth zinc borate glasses were present in octahedral sites with tetragonal distortion. The spin concentration (N) participating in resonance was calculated as a function of temperature for strontium zinc borate (SrZB) glass sample containing 0.7 wt.% of Cu²⁺ ions and the activation energy was calculated. From the EPR data, the paramagnetic susceptibility (χ) was calculated at different temperatures and the Curie constant was evaluated from the 1/χ-T graph. The optical absorption spectra of these samples show only one absorption band. The optical band gap energies (E_g) and Urbach energy (ΔE) are calculated from their ultraviolet edges. The FTIR studies show different stretching and bending vibrations of alkaline earth zinc borate glasses.     

Polarons in boron doped iron phosphate glasses

The electrical conductivity and dielectric properties of xB₂O₃–(40 ? x)Fe₂O₃–60P₂O₅ (x = 6–20, mol%) glasses were investigated in the frequency range from 0.01 Hz to 1 MHz and the temperature range from 303 K to 523 K. At temperatures below 523 K an ac conductivity and the dielectric constant follow the universal dielectric response (UDR), being typical for hopping or tunneling of localized charge carriers. A detailed analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for tunneling of small polarons revealed that below 523 K this mechanism governs the charge transport in these glasses. The comparison of the values of characteristic coefficients W_∞ and α determined by two different methods confirms the polaronic behavior of boron doped iron phosphate glasses.     

Synthesis and structure–property relations in xCuO–(1 − x)Bi2O3 (0.5 ⩽ x ⩽ 0.9) (C1–C5: x = 0.5, 0.6, 0.7, 0.8, 0.9) glasses

Synthesis of the xCuO–(1 ? x)Bi₂O₃ (0.5 ? x ? 0.9) (C1–C5: x = 0.5, 0.6, 0.7, 0.8, 0.9) glasses was done via nitrate–citrate gel route. Glassy phase is ascertained by XRD studies. Magnetic susceptibility results in the range 4.2–400 K show weak paramagnetic nature with exchange integrals ～0.024–0.13 eV in the glasses. The electron paramagnetic resonance (EPR) in the range 4.2–363 K shows g ≈ 2.0 and the trend of the g-matrix elements g_|| > g_⊥ > g_e for the glasses C1–C5 at 4.2 K are due to the Cu²⁺ (3d⁹) paramagnetic site in the glasses which is in a tetragonally elongated octahedron [O_1/2–CuO_4/2–O_1/2] having D_4h symmetry. IR spectroscopic results show the presence of octahedron [BiO_6/2]^3? and [CuO_6/2]^4? units and pyramidal [BiO_2/2O]^? unit in the glasses.     

ArF laser induced pulse absorption in fused silica (type III): Modeling the fluence and repetition rate dependence

At 193 nm, weak stationary bulk absorption coefficients α^stat in standard and experimental grade fused silica (type III) are measured in dependence on the laser fluence H and repetition rate f. The samples show non-linear increases α^stat(H) for 0.2 ? H ? 5 mJ cm^?2 pulse^?1 (f = const.) and α^stat(f) for 100 ? f ? 1000 Hz (H = const.). An absorption model, focussing on ArF laser induced E′ center generation and annealing, and the associated rate equations are applied to simulate the experimental data quantitatively. From the simulations, material parameters like the 2-photon absorption (TPA) coefficient, the E′ center absorption cross section σ_E′ and the hydrogen related E′ annealing rate are calculated. TPA coefficients values of 9.7 · 10^?9 cm/W (standard grade material) and 1.4 · 10^?8 cm/W (experimental grade material), E′ center cross sections of 4.5 · 10^?18 and 3.6 · 10^?18 cm² and hydrogen annealing rates of 1.5 s^?1 (standard grade) and 3.4 s^?1 (experimental grade) are found.     

Tensile properties of ZrCu-based bulk metallic glasses at ambient and cryogenic temperatures

The tensile behaviors of a series of (Zr_47.5Cu_47.5Al₅)_1 ? x(Zr₈₀Nb₂₀)_x (x = 0, 0.05, 0.10, 0.15) bulk metallic glasses were studied at ambient and cryogenic (77 K) temperatures. It is found that the tensile strength of the alloys increases as the temperature decreases from 298 K to 77 K. The maximum enhancement is 15.7%, and the toughness of these alloys does not deteriorate at low temperatures. We demonstrate that the higher energy required to raise the temperature in the shear bands from the cryogenic temperature to glass transition temperature is the origin of the tensile strength enhancement at low temperatures.     

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.     

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.     

The shoving model for the glass-former LiCl·6H2O: A molecular dynamics simulation study

Molecular dynamics (MD) simulations of LiCl·6H₂O showed that the diffusion coefficient D, and also the structural relaxation time <τ>, follow a power law at high temperatures, D^?1 ∝ (T ? T_o)^?μ, with the same experimental parameters for viscosity (T_o = 207 K, μ = 2.08). Decoupling between D and <τ> occurs at T_x ～ 1.1T_o. High frequency acoustic excitations for the LiCl·6H₂O model were obtained by the calculation of time correlation functions of mass current fluctuations. The temperature dependence of the instantaneous shear modulus, G_∞(T), was considered in the shoving model for supercooled liquids [J.C. Dyre, T. Christensen, N.B. Olsen, J. Non-Cryst. Solids 352 (2006) 4635] resulting in a linear relationship log (D^?1) vs. G_∞/T.     

Octahedral fluoride glasses: Raman spectra and structure of niobium pentafluoride

Raman spectroscopy is used to characterize the NbF₅ phases in the temperature range 80–500 K. A new clear glass is formed by quenching the melt to liquid nitrogen temperatures having a glass transition at ～206 K and crystallization at ～233 K. For all phases including the melt, the glass, the supercooled liquid, the crystalline solid and the gas, the Raman spectra show a rather common high frequency band at ～760 cm^?1 which is attributed to the Nb–F terminal frequency of partially bridged ‘NbF₆’ octahedra. Based on the systematics of the Raman spectra for all phases and the literature physicochemical data a model is proposed for the glass and the liquid phases where ‘NbF₆’ octahedral bridged in cis and/or trans configurations form a variety of cyclic and/or chain structures which intermix building up the overall structure. At exceptionally low energies (<11 cm^?1) a rather weak in intensity Boson peak is observed in the glass which shifts to even lower energies with increasing temperature. Librational and/or tortional motions of the bridged octahedra participating in the glass structure are possible candidates for the origin of this peak.     

Electrical conductivity and dielectric relaxation in non-crystalline films of tungsten trioxide

Amorphous tungsten trioxide (a-WO₃) thin films were prepared by thermal evaporation technique. The electrical conductivity and dielectric properties of the prepared films have been investigated in the frequency range from 100 Hz to 100 kHz and in the temperature range 293–393 K. In spite of the absence of the dielectric loss peaks, application of the dielectric modulus formulism gives a simple method for evaluating the activation energy of the dielectric relaxation. The frequency dependence of σ(ω) follows the Jonscher’s universal dynamic law with the relation σ(ω) = σ_dc + Aω^s, where s is the frequency exponent. The conductivity in the direct regime, σ_dc, is described by the small polaron model. The electrical conductivity and dielectric properties show that Hunt’s model is well adapted to a-WO₃ films.     

Magnetic interactions in frustrated Mn3Fe4(VO4)6

Magnetic interactions in a site-disordered multicomponent vanadate Mn₃Fe₄(VO₄)₆ are studied using DC magnetization and multifrequency Electron Paramagnetic Resonance (EPR). The static magnetic susceptibility χ shows antiferromagnetic interactions between Fe³⁺ and Mn²⁺ spins with a Curie–Weiss temperature Θ = ?165(5) K. EPR measurements indicate a strong dependence of χ on the frequency and temperature. The EPR spectra due to iron and manganese ions are observed in the X-band. It is mostly manganese ions that are observed at 80 GHz while two kinds of magnetic centers are identified at frequencies above 160 GHz. The observed shifts of the resonance lines for Fe³⁺ ions at low frequencies differ from those at high frequencies. The observed features may be due to different magnetic sublattices which modify the magnetic ground state, while competing magnetic interactions may lead to magnetic frustration. It appears that the very high magnetic fields employed in our high-frequency EPR measurements may affect the spin-flop transitions anticipated below Neel temperature T_N.     

Synthesis and characterization of TM-doped CuO (TM = Fe,Ni)

Polycrystalline Cu_1?xTM_xO samples (x = 0 and 0.06; TM = Ni²⁺ and Fe³⁺) were grown using a co-precipitation method. The structural and magnetic properties were investigated by means of temperature dependent magnetic susceptibility and room temperature X-ray powder diffraction (XRPD). The XRPD analyses of the samples reveal the formation of single phase with structure isomorphous to the CuO. Interestingly, T-dependent magnetization shows the reduction of Néel temperature, T_N, from 213 K in the copper oxide to 70 K in the Fe-doped sample (x = 0.06). Because in the Ni-doped samples T_N seems to be unaffected, this decrease in T_N is believed to be due to the different electronic structure of the dopant. The ferromagnetic behavior observed at room temperature in all samples can be related to both the level of oxygen (excess or vacancy) of our samples and to the difference in the magnetic structure of the dopant.     

Time resolved thermal lens measurements of the thermo-optical properties of Nd2O3-doped low silica calcium aluminosilicate glasses down to 4.3 K

In this work, the thermal lens spectrometry was applied to measure the thermo-optical properties of Nd₂O₃-doped low silica calcium aluminosilicate glasses as a function of temperature, between 4.3 and 300 K. The thermal relaxation calorimetry was used to determine the specific heat, c_p. The results showed a decrease of the thermal diffusivity of about one order of magnitude from 4.3 K up to 300 K, with a T^?1 dependence in the interval between 20 and 70 K and a T^?0.35 between 4.3 and 20 K. The fluorescence quantum efficiencies of the doped samples were calculated down to 50 K, showing a variation of the order of 12% and 25% for the samples with 0.6 and 1.04 mol% of Nd₂O₃, respectively. In addition, the temperature corresponding to the maximum in c_p/T³, the so-called boson peak, was observed at about 17 K for the undoped sample and at lower temperatures for the doped glasses. In conclusion, our results showed the ability of the time resolved thermal lens to determine the thermo-optical properties of glasses at temperatures lower than 300 K, bringing new possibilities for experiments in a wide range of optical materials.