Dynamics of Li+ ions in strontium metaphosphate glasses

Dynamics of Li+ ions in strontium metaphosphate glasses has been studied in the frequency range of 10 Hz-2 MHz and in the temperature range of 273-573 K. The dc conductivity increases and the activation energy decreases with the replacement of strontium ions by lithium ions in the glass compositions. The ac electrical data have been studied using the modulus and conductivity formalisms. We have observed that the stretching exponent decreases and the frequency exponent increases with the replacement of strontium ions by lithium ions in these glasses. The variation of these parameters was explained in terms of ion-ion interaction. The mobile ion concentration remains nearly constant, which indicates that the mobility of the migrating ions increases when the alkaline earth ions are replaced by the alkali ions.     

Dynamics of lithium ions in calcium bismuthate glasses

Ion transport in Li(2)O-CaO-Bi(2)O(3) glasses has been studied in the frequency range from 10 Hz to 2 MHz and in the temperature range from 293 to 543 K. The variation of the dc conductivity and the activation energy of these glasses with composition have been compared with those of binary lithium bismuthate glasses. It has been observed that the introduction of CaO in small amount does not effect the dc conductivity and the corresponding activation energy, but the larger amount of CaO changes them to some extent. The frequency-dependent conductivity has been studied using both conductivity and modulus formalisms. The values of the nonexponential parameter and frequency exponent are found to differ for the Li(2)O-CaO-Bi(2)O(3) glasses from those for the binary Li(2)O-Bi(2)O(3) glasses. The concentration of mobile Li(+) ions does not change appreciably with the change in the Li(2)O as well as CaO content in the compositions. The increasing amount of CaO in the glass compositions for fixed Li(2)O content points out that CaO dilates the glass network, enhancing the migration of Li(+) ions.     

Correlation of ion dynamics and structure of superionic tellurite glasses

Ion dynamics and structure of a series of superionic AgI-doped silver tellurite glasses have been investigated in this paper. The composition dependence of the dc conductivity and the activation energy of these glasses has been compared with those of AgI-doped silver phosphate and borate glasses. We have observed that the conductivity increases and the activation energy decreases with increase of AgI content and that the tellurite glasses have higher conductivity than those for phosphate or borate glasses. We have analyzed the ac electrical data in the framework of the power law and the electric modulus formalisms. We have established a correlation between the crossover rate of the mobile silver ions and the rearrangement of the structural units in tellurite glasses. The scaling of the conductivity spectra has been used to interpret the temperature and composition dependence of the relaxation dynamics. Analysis of the dielectric relaxation in the framework of modulus formalism indicates an increase in the ion-ion cooperation in the glass compositions with increasing AgI content.     

Relaxation dynamics in AgI-doped silver vanadate superionic glasses

Relaxation dynamics of Ag+ ions in several series of AgI-Ag2O-V2O5 superionic glasses has been studied in the frequency range from 10 Hz to 2 MHz and in the temperature range from 93 to 323 K. The composition dependence of the dc conductivity and the activation energy of these glasses has been compared with those of AgI-doped silver phosphate and borate glasses. The frequency-dependent electrical data have been analyzed in the framework of conductivity formalism. We have obtained the mobile ion concentration and the power-law exponent from the analysis of the conductivity spectra. We have observed that the concentration of Ag+ ions is independent of temperature and the conductivity is primarily determined by the mobility. A fraction of the Ag+ ions in the glass compositions are involved in the dynamic process. We have also shown that the power-law exponent is independent of temperature. The results are also supported by the temperature and composition independence of the scaling of the conductivity spectra.     

Electrical conductivity and relaxation in mixed alkali tellurite glasses

The authors have reported the electrical conductivity and the conductivity relaxation in mixed alkali tellurite glasses of compositions of 70TeO2-xNa2O-(30-x)Li2O in the frequency range from 10 Hz to 2 MHz and in the temperature range from room temperature to just below the glass transition temperature. They have analyzed the relaxation data in the framework of different models. They have observed the mixed alkali effect in the dc and ac conductivities, the crossover frequency, and the conductivity relaxation frequency as well as in their respective activation energies in these glasses. They have also observed the mixed alkali effect in the decoupling index. The scaling property of the modulus spectra of these mixed alkali glasses shows that the conductivity relaxation in the mixed alkali tellurite glasses is independent of temperature but depends on the glass compositions.     

"Cooperativity blockage" in the mixed alkali effect as revealed by molecular-dynamics simulations of alkali metasilicate glass

The relaxation dynamics of a complex interacting system can be drastically changed when mixing with another component having different dynamics. In this work, we elucidate the effect of the less mobile guest ions on the dynamics of the more mobile host ions in mixed alkali glasses by molecular-dynamics (MD) simulations. One MD simulation was carried out on lithium metasilicate glass with the guest ions created by freezing some randomly chosen lithium ions at their initial locations at 700 K. A remarkable slowing down of the dynamics of the majority mobile Li ions was observed both in the self-part of the density-density correlation function, Fs(k,t), and in the mean-squared displacements. On the other hand, there is no significant change in the structure. The motion of the Li ions in the unadulterated Li metasilicate glass is dynamically heterogeneous. In the present work, the fast and slow ions were divided into two groups. The number of fast ions, which shows faster dynamics (Levy flight) facilitated by cooperative jumps, decreases considerably when small amount of Li ions are frozen. Consequently there is a large overall reduction of the mobility of the Li ions. The result is also in accordance with the experimental finding in mixed alkali silicate glasses that the most dramatic reduction of ionic conductivity occurs in the dilute foreign alkali limit. Similar suppression of the cooperative jumps is observed in the MD simulation data of mixed alkali system, LiKSiO3. Naturally, the effect found here is appropriately described as "cooperativity blockage." Slowing down of the motion of Li ions also was observed when a small number of oxygen atoms chosen at random were frozen. The effect is smaller than the case of freezing some the Li ions, but it is not negligible. The cooperativity blockage is also implemented by confining the Li metasilicate glass inside two parallel walls formed by freezing Li ions in the same metasilicate glass. Molecular-dynamics simulations were performed on the dynamics of the Li ions in the confined glass. Slowing down of the dynamics is largest near the wall and decreases monotonically with distance away from the wall.     

EPR and optical investigations of manganese ions in alkali lead tetraborate glasses

Electron paramagnetic resonance (EPR) and optical absorption spectra of Mn2+ ions in different alkali lead tetraborate glasses 90R2B4O7+9.25PbO+0.75MnSO4 (R=Li, Na and K) and 90Li2B4O7+(10-x)PbO+xMnSO4 (x=0.1, 0.25, 0.5, 0.75, 1.0, 1.25, 1.5 and 2 mol%) have been studied. The EPR spectrum of all the glass samples exhibit three resonance signals at g=2.0, 3.3 and 4.3. The resonance signal at g=2.0 is attributed to the Mn2+ ions in an environment close to an octahedral symmetry. The resonance signals at g=3.3 and 4.3 have been attributed to the rhombic symmetry of the Mn2+ ions. The effect of temperature (123-433 K) and the composition dependence of EPR signals have been studied for Mn2+ ions in lithium lead tetraborate glasses. It is interesting to observe that the variation of paramagnetic susceptibility (chi) with temperature obeys Curie-Weiss law. From the slope of 1/chi versus T graph, the Curie constant (C) has been evaluated. The zero-field splitting (zfs) parameter D has been calculated for different alkali lead tetraborate glasses from the intensities of the allowed hyperfine lines. The optical absorption spectrum exhibits three bands. An intense and broad band at lower energy side has been assigned to the spin-allowed (5Eg-->5T2g) transition of Mn3+ ions in an octahedral symmetry. The intense and sharp band and a broad band at higher energy side have been assigned to charge transfer bands. A red shift is observed with increase of alkali ion size. The optical band gap energy (Eopt) decreases, whereas the Urbach energies (DeltaE) increases with increase of Mn content. The theoretical values of optical basicity (Lambdath) of the glasses have also been evaluated.     

Fe(3+) ions in alkali lead tetraborate glasses--an electron paramagnetic resonance and optical study

Glass systems of composition 90R(2)B(4)O(7)+9PbO+1Fe(2)O(3) (R=Li, Na and K) and 90Li(2)B(4)O(7)+(10-x)PbO+xFe(2)O(3) (x=0.5, 1, 3, 4, 5, 7 and 9 mol %) have been investigated by means of electron paramagnetic resonance (EPR) and optical absorption techniques. The EPR spectra exhibit three resonance signals at g approximately 6.0, 4.2 and 2.0. The resonances at g approximately 6.0 and 4.2 are attributed to Fe(3+) ions in rhombic and axial symmetry sites, respectively. The g approximately 2.0 resonance signal is due to two or more Fe(3+) ions coupled together with dipolar interaction. The EPR spectra of 1 mol % of Fe(2)O(3) doped in lithium lead tetraborate glass samples have been studied at different temperatures (123-433 K). The intensity of g approximately 4.2 resonance signal decreases and the intensity of g approximately 2.0 resonance signal increases with the increase of temperature. The line widths are found to be independent of temperature. The EPR spectra exhibit a marked concentration dependence on iron content. A decrease in intensity for the resonance signal at g approximately 4.2 with increase in iron content for more than 4 mol % has been observed in lithium lead tetraborate glass samples and this has been attributed to the formation of Fe(3+) ion clusters in the glass samples. The paramagnetic susceptibility (chi) is calculated from the EPR data at various temperatures and the Curie constant (C) has been evaluated from 1/chi versus T graph. The optical absorption spectrum of Fe(3+) ions in lithium lead tetraborate glasses exhibits three bands characteristic of Fe(3+) ions in an octahedral symmetry. The crystal field parameter D(q) and the Racah interelectronic repulsion parameters B and C have also been evaluated. The value of interelectronic repulsion parameter B (825 cm(-1)) obtained in the present work suggests that the bonding is moderately covalent.     

Anomalous ionic conductivity increase in Li2S + GeS2 + GeO2 glasses

Numerous studies of the ionic conductivities in oxide-doped chalcogenaide glasses have shown the anomalous result that the ionic conductivity actually increases significantly (by more than a factor of 10 in some cases) by the initial addition of an oxide phase to a pure sulfide glass. After this initial sharp increase, the conductivity then monotonically decreases with further oxide addition. While this behavior is important to the application of these glasses for Li batteries, no definitive understanding of this behavior has been elucidated. To examine this effect further and more completely, the ionic conductivities of 0.5Li(2)S + 0.5[(1 - x)GeS(2) + xGeO(2)] glasses have been measured on disc-type bulk glasses. The ionic conductivity of the 0.5Li(2)S + 0.5GeS(2) (x = 0) glass was observed to increase from 4.3 x 10(-5) (Omega cm)(-1) to 1.5 x 10(-4) (Omega cm)(-1) while the activation energy decreased to 0.358 eV from 0.385 eV by the addition of 5 mol % of GeO(2). Further addition of GeO(2) monotonically decreased the conductivity and increased the activation energy. On the basis of our previous studies of the structure of this glass system, the Anderson and Stuart model was applied to explain the decrease in the activation energy and increase in the conductivity. It is suggested that the "doorway" radius between adjacent cation sites increases slightly (from approximately 0.29(+/-0.05) A to approximately 0.40(+/-0.05) A) with the addition of oxygen to the glass and is proposed to be the major cause in decreasing the activation energy and thereby increasing the conductivity. Further addition of oxides appears to contract the glass structure (and the doorway radius) leading to an increase in the conductivity activation energy and a decrease in the conductivity.     

Conductivity and modulus formulation in lithium modified bismuth zinc borate glasses

The conductivity and modulus formulation in lithium modified bismuth zinc borate glasses with compositions xLi₂O–(50-x) Bi₂O₃–10ZnO–40B₂O₃ has been studied in the frequency range 0.1 Hz–1.5 × 10⁵ Hz in the temperature range 573 K–693 K. The temperature and frequency dependent conductivity is found to obey Jonscher's universal power law for all the studied compositions, the dc conductivity (σ_dc), crossover frequency (ω_H), and frequency exponent (s) have been estimated from the fitting of the experimental data of ac conductivity with Jonscher's universal power law. Enthalpy to dissociate the cation from its original site next to a charge compensating centre (H_f) and enthalpy of migration (H_m) have been estimated. It has been observed that number of charge carriers and ac conductivity in the lithium modified bismuth zinc borate glasses increases with increase in Li₂O content. Further, the conduction mechanism in the glass sample with x = 0 may be due to overlapping large polaron tunneling, whereas, conduction mechanism in other studied glass samples more or less follows diffusion controlled relaxation model. The ac conductivity is scaled using σ_dc and ω_H as the scaling parameter and is found that these are suitable scaling parameter for conductivity scaling. Non-Debye type relaxation is found prevalent in the studied glass system. Scaling of ac conductivity as well as electric modulus confirms the presence of different type of conduction mechanism in the glass samples with x = 0 and 5 from other studied samples. The activation energy of relaxation (E_R) and dc conductivity (E_dc) are almost equal, suggesting that polarons/ions have to overcome same barrier while relaxing and conducting.     

Self-diffusion of lithium in LiAlSi2O6 glasses studied using mass spectrometry

In order to improve our understanding of the transport mechanisms of lithium in glasses, we have performed diffusion and ionic conductivity studies on spodumene composition (LiAlSi(2)O(6)) glasses. In diffusion couple experiments pairs of chemically identical glasses with different lithium isotopy (natural Li vs pure (7)Li) were processed at temperatures between 482 and 732 K. Profiles of lithium isotopes were measured after the diffusion runs innovatively applying femtosecond UV laser ablation combined with inductively coupled plasma mass spectrometry (LA ICP-MS). Self-diffusion coefficients of lithium in the glasses were determined by fitting the isotope profiles. During some of the diffusion experiments the electrical conductivity of the samples was intermittently measured by impedance spectrometry. Combining ionic conductivity and self-diffusivity yields a temperature-independent correlation factor of ~0.50, indicating that motions of Li ions are strongly correlated in this type of glasses. Lithium self-diffusivity in LiAlSi(2)O(6) glass was found to be very similar to that in lithium silicate glasses although Raman spectroscopy demonstrates structural differences between these glasses; that is, the aluminosilicate is completely polymerized while the lithium silicate glasses contain large fractions of nonbridging oxygen.     

Hopping rates and concentrations of mobile fluoride ions in Pb(1-x)Sn(x)F(2) solid solutions

In the present paper, the ion dynamics and relaxation of fluoride ions in Pb(1-x)Sn(x)F(2) (with x=0.2-0.6) solid solutions, prepared by mechanochemical milling, are studied in the conductivity formalism over wide ranges of frequencies and temperatures. The conductivity spectra of the investigated materials are analyzed by the Almond-West (AW) power-law model. The estimated values of the hopping rates and the dc conductivity of different compositions are thermally activated with almost the same activation energy. The calculated values of the concentration of mobile ions, n(c), are almost independent of temperature and composition for x=0.2-0.4. The maximum value of n(c) is obtained for the x=0.6 sample, although it does not show the maximum conductivity. Therefore, the composition dependence of the ionic conductivity of these solid solutions could be explained based on the extracted parameters. The results presented in the current work indicate that the AW model represents a reasonable approximation of the overall frequency-dependent conductivity behavior of the investigated materials. The conductivity spectra at different temperatures for each composition are successfully scaled to a single master curve, indicating a temperature-independent relaxation mechanism. For different compositions, however, the conductivity spectra cannot be scaled properly, indicating composition-dependent relaxation dynamics.     

NMR study of Li+ ion dynamics in the perovskite Li(3x)La(1/3-x)NbO3

(7)Li and (6)Li nuclear magnetic resonance (NMR) experiments are carried out on the perovskite Li(3x)La(1/3-x)NbO(3). The results are compared to those obtained on the titanate Li(3x)La(2/3-x)TiO3 (LLTO) in order to investigate the effect, on the lithium ion dynamics, of the total substitution of Nb(5+) for Ti(4+) in the B-site of the ABO(3) perovskites. The XRD patterns analysis reveals that this substitution leads to a change in the distribution of the La(3+) ions in the structure. La(3+) ions distribution is very important, in regard to ionic conductivity, because these immobile ions can be considered as obstacles for the long-range Li+ motion. If compared to the titanates, the compounds of the niobate solid solution have a bigger unit cell volume, a smaller number of La(3+) ions, and a higher number of vacancies. These should favor the motion of the mobile ions into the structure. This is not experimentally observed. Therefore, the interactions between the mobile species and their environment greatly influence their mobility. (7)Li and (6)Li NMR relaxation time experiments reveal that the Li relaxation mechanism is not dominated by quadrupolar interaction. (7)Li NMR spectra reveal the presence of different Li+ ion sites. Some Li+ ions reside in an isotropic environment with no distortion, some others reside in weakly distorted environments. T(1), T(1)(rho), and T(2) experiments allow us to evidence two motions of Li+. As in LLTO, T(1) probes a fast motion of the Li+ ions inside the A-cage of the perovskite structure and T(1)(rho) a slow motion of these ions from A-cage to A-cage. At variance with what has been observed in LLTO, these different Li+ ions can be differentiated through the spin-lattice relaxation times, T(1) and T(1)(rho), as well as through the transverse relaxation time, T(2).     

Nuclear magnetic resonance investigation of dynamics in poly(ethylene oxide)-based lithium polyether-ester-sulfonate ionomers

Nuclear magnetic resonance spectroscopy has been utilized to investigate the dynamics of poly(ethylene oxide)-based lithium sulfonate ionomer samples that have low glass transition temperatures. (1)H and (7)Li spin-lattice relaxation times (T(1)) of the bulk polymer and lithium ions, respectively, were measured and analyzed in samples with a range of ion contents. The temperature dependence of T(1) values along with the presence of minima in T(1) as a function of temperature enabled correlation times and activation energies to be obtained for both the segmental motion of the polymer backbone and the hopping motion of lithium cations. Similar activation energies for motion of both the polymer and lithium ions in the samples with lower ion content indicate that the polymer segmental motion and lithium ion hopping motion are correlated in these samples, even though lithium hopping is about ten times slower than the segmental motion. A divergent trend is observed for correlation times and activation energies of the highest ion content sample with 100% lithium sulfonation due to the presence of ionic aggregation. Details of the polymer and cation dynamics on the nanosecond timescale are discussed and complement the findings of X-ray scattering and quasi-elastic neutron scattering experiments.     

Fluorescence properties of Eu3+ ions doped borate and fluoroborate glasses containing lithium, zinc and lead

The influence of glass composition on the fluorescence properties of Eu3+ ions doped borate and fluoroborate glasses modified with Li+, Zn2+ and Pb2+ cations have been investigated. The magnitude of splittings of 7F1 levels are analyzed using crystal-field (CF) analysis. The relative intensities of 5D0 --> 7F2 to 5D0 --> 7F1 transitions, crystal-field strength parameters and decay times of the 5D0 level have been determined and are found to be lower for Pb based glasses than those of Zn/Li based glasses. The lifetimes of 5D0 level are found to increase when borate glasses are modified with pure fluorides than with oxides and oxyfluorides. The fluorescence decay of 5D0 level fits perfect single exponential in the Eu3+:glass systems studied which indicates the absence of energy transfer between Eu3+ ions in these glasses.     

Collisional activation of ions formed by [Li]+ ion attachment

Since no unimolecular fragmentation is observed with [M+Li]⁺ ions under normal operating conditions the collisional activation method was used to study the fragmentation behaviour of these ions. It was found that the liberation of the [Li]⁺ ion is a dominant process only with smaller molecules. In addition, direct bond cleavages and new types of rearrangement reactions lead to fragment ions in which the lithium is normally retained. The decomposition behaviour of [M+Li]⁺ ions represents an intermediate case between that of [M]+ ions and excited neutral molecules and is quite different from that of [M+H]⁺ ions.     

Structural investigations on sodium-lead borophosphate glasses doped with vanadyl ions

Electron paramagnetic resonance (EPR), optical absorption, and FT-IR spectra of vanadyl ions in the sodium-lead borophosphate (Na(2)O-PbO-B(2)O(3)-P(2)O(5)) (SLBP) glass system have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of VO(2+) ions. The spin Hamiltonian parameters g and A are found to be independent of the V(2)O(5) content and temperature. The values of the spin Hamiltonian parameters indicate that the VO(2+) ions in SLBP glasses are present in octahedral sites with tetragonal compression. The population difference between Zeeman levels (N) is calculated as a function of temperature for an SLBP glass sample containing 1.0 mol % VO(2+) ions. From the EPR data, the paramagnetic susceptibility (χ) is calculated at different temperatures, and the Curie constant (C) is calculated from the 1/χ versus T graph. The optical absorption spectra of the glass samples show two absorption bands, and they are attributed to V(3+) and V(4+) ions. The optical band gap energy (E(opt)) and Urbach energy (ΔE) are calculated from their ultraviolet absorption edges. It is observed that, as the vanadium ion concentration increases, E(opt) decreases and ΔE increases. The study of the IR absorption spectrum depicts the presence of BO(3), BO(4), PO(3), PO(4), and VO(5) structural units.     

PVP-LiCl-DMF溶液体系的流变学特性及相互作用

利用流变学方法, 采用核磁共振和红外光谱技术开展了聚乙烯吡咯烷酮(PVP)和LiCl相互作用研究, PVP/LiCl/DMF浓溶液的表观粘度随着LiCl含量的增加而提高, 溶液的粘流活化能也相应增加. 13C NMR结果表明, 溶液中Li+与PVP的羰基之间存在相互作用, 这种相互作用改变了PVP分子的聚集状态. 红外光谱结果证实了PVP/LiCl复合物中Li+与PVP的羰基存在相互作用.     

VO2+ ions in zinc lead borate glasses studied by EPR and optical absorption techniques

Electron paramagnetic resonance (EPR) and optical absorption spectra of vanadyl ions in zinc lead borate (ZnO-PbO-B2O3) glass system have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of VO2+ ions. The values of spin-Hamiltonian parameters indicate that the VO2+ ions in zinc lead borate glasses were present in octahedral sites with tetragonal compression and belong to C4V symmetry. The spin-Hamiltonian parameters g and A are found to be independent of V2O5 content and temperature but changing with ZnO content. The decrease in Deltag( parallel)/Deltag( perpendicular) value with increase in ZnO content indicates that the symmetry around VO2+ ions is more octahedral. The decrease in intensity of EPR signal above 10 mol% of V2O5 is attributed to a fall in the ratio of the number of V4+ ions (N4) to the number of V5+ ions (N5). The number of spins (N) participating in resonance was calculated as a function of temperature for VO2+ doped zinc lead borate glass sample and the activation energy was calculated. From the EPR data, the paramagnetic susceptibility was calculated at various temperatures and the Curie constant was evaluated from the 1/chi-T graph. The optical absorption spectra show single absorption band due to VO2+ ions in tetragonally distorted octahedral sites.