Mixed Mobile Ion Effect Research Articles

Crystallization behavior and properties of quartz glass-ceramics synthesized from desert sand

Quartz glass-ceramics were synthesized with desert sand as the main raw material. The effects of pretreatment technology of desert sand and various cations on the glass stability (GS) parameters (KH, KLL,KW, KZW, KLX), crystallization kinetic parameters (crystallization activation energy (Ec), reaction rate (k), the effective frequency factor(ν) and the Avrami parameter (n)), phase transition, microstructure and properties of glass-ceramics were investigated. The results show that the chemical composition of desert sand is greatly changed by sieving and magnetic separation, and the glass stability, phase transition and crystallization ability of glass are controlled by the mixed mobile ion effect (MMIE), in which the ionic field intensity determined by ionic valence and radius plays a major role. Finally, the crystallization of glass is dominated by the surface crystallization mechanism, and the obtained glass-ceramics mainly consist of α-quartz, β-cristobalite and glass phases, which have excellent comprehensive properties.

Mixed mobile ion effect in borosilicate glasses doped with cadmium sulfoselenide and silver and copper iodides

We report measurements of dynamic (a.c.) electrical conductivity in borosilicate glasses doped with cadmium sulfoselenide and copper and silver iodides in a wide temperature range below the glass transition temperature Tg and at different frequencies. The concentration of the mobile dopant ions is governed by specific heat treatment conditions of the glass samples leading to a creation of the CdSSe, AgI and CuI semiconductor nanocrystals. Investigations include different cases from a full solution of the dopant ions coming from a dissociation of the dopants during the glass preparation to their almost complete incorporation into the nanocrystals in the glass matrix. At temperatures higher than 150 °C–200 °C the a.c. conductivity in all the examined glasses exhibits the Arrhenius behavior. In this temperature range the mixed mobile ion effect is detected: the doped glasses have the low values of the conductivity compared to the undoped ones. In the low temperature range only weak temperature dependence is detected for all the samples. The mixed mobile ion effect is still presented for the CdSSe-doped glasses, whereas the AgI- and CuI-doped glasses exhibit the classical MMIE which is essentially absent at low temperatures.

High capacity all-solid-state Cu–Li2S/Li6PS5Br/In batteries

Abstract Inorganic lithium ion fast conductor Li 6 PS 5 Br has high ionic conductivity and consequently is promising as solid electrolyte in all-solid-state lithium secondary batteries. Here we fabricated Li 6 PS 5 Br by ball milling and subsequent heat treatment. The argyrodite phase already formed at 300 °C and is electrochemically stable between 0 and 4 V. Preparing Cu–Li 2 S–argyrodite composite cathode mixtures by ball milling increases the initial charge and discharge capacity of all-solid-state Cu–Li 2 S/Li 6 PS 5 Br/In batteries compared to mortar-ground composite cathode mixtures. A charge capacity of 500 mAh/g and discharge capacity of 445 mAh/g were achieved using composite cathode powder ball milled for 30 min. However, batteries using composite cathode prepared by either method show similar reversible discharge capacity for a range of C rates as the capacity is mainly limited by volume change of cathode material and the mixed mobile ion effect. Rietveld refinements after 20 cycles show an incomplete conversion stage with partial Cu + for Li + insertion both in the active material and the solid electrolyte.

Electrical conductivity of copper lithium phosphate glasses

Copper based oxide glasses are especially interesting for the possibility of ionic-electronic mixed conduction, which has potential applications in energy and switching devices. Accordingly, lithium metaphosphate glasses are investigated within the (100-x) Li2O - xCu2O - 50P2O5 series, where Li+ ions are gradually replaced by copper ions. Based on the changes in glass transition temperature and thermal stability via structural modification, the glasses are shown to be predominantly ionic conductors. In fact, they exhibit signs of classic mixed mobile ion effect (MMIE), a hallmark of ion conduction in glass, which would be due to Li+ and Cu+ ions in the present case.

Effect of lithium-to-magnesium ratio in metaphosphate glasses on crack-tip condensation and sub-critical crack growth

Corner cracks were initiated in a series of lithium–magnesium-metaphosphate glasses with different Li-to-Mg ratios by performing Vickers indentation under humid conditions (RH=50% and RH=65%) and in dry nitrogen gas atmosphere (RH=0.01%). Propagation of each crack was observed up to 240h. Distinct condensation of water at the crack-tip up to 30μm occurred in humid environments, which led to a decrease in open crack length, while in dry nitrogen gas atmosphere this phenomenon was absent. A square root of time dependence was observed for the crack-tip condensation (CTC) kinetics as well as for weight gain experiments on crack-free glass specimens. Slow crack growth and CTC were dependent on the Li-to-Mg ratio of the glasses and showed a negative deviation from a linear compositional trend. Deviation of CTC was largest for glasses of Li-to-Mg ratio >2:1 indicating a mixed mobile ion effect beyond charge neutrality, while the fatigue resistance exhibited a maximum at concentrations of equal charge. On the other hand a positive deviation from additivity was found for hardness and Young's modulus indicating increased resistance against elastic and plastic deformation for glass compositions of mixed Li+ and Mg2+ ions.

Mixed mobile ion effect on a.c. conductivity of boroarsenate glasses

In this article we report the study of mixed mobile ion effect (MMIE) in boroarsenate glasses. DSC and a.c. electrical conductivity studies have been carried out for \(\boldsymbol{x}\)MgO–(25\(\boldsymbol{-}\) \(\boldsymbol{x}\))Li 2 O–50B 2 O 3 –25As 2 O 3 glasses. It is observed that strength of MMIE in a.c. conductivity is less pronounced with increase in temperature and frequency. The results were explained on the basis of structural model (SM) proposed by Swenson and his co-workers supporting molecular dynamic results.

A weak mixed mobile ion effect in vanadium–tellurite oxide glass modified by silver and lithium cations

The effect of the partial replacement of lithium oxide by silver oxide in a glassy vanadium–molybdenum–tellurite oxides matrix is analyzed by means of impedance spectroscopy. We find that a weak mixed mobile ion effect (MMIE) is due to the different kind of modifications silver and lithium oxides induce in the glass of formula 0.7[ x Ag 2O (1 − x) Li 2O] 0.3[0.5 V 2O 5 0.5 MoO 3] 2 TeO 2.

Defect model for the mixed mobile ion effect revisited: An importance of deformation rates

The progress in understanding the behavior of glassy mixed ionic conductors within the concept of the defect model for the mixed mobile ion effect [V. Belostotsky, J. Non-Cryst. Solids 353 (2007) 1078] is reported. It is shown that in a mixed ionic conductor (e.g., mixed alkali glass) containing two or more types of dissimilar mobile ions of unequal size sufficient local strain arising from the size mismatch of a mobile ion entering a foreign site cannot be, in principle, absorbed by the surrounding network-forming matrix without its damage. Primary site rearrangement occurs immediately, on the time scale close to that of the ion migration process, through the formation of intrinsic defects in the nearest glass network. Neither anelastic relaxation below glass transition temperature, T g, nor viscoelastic or viscous behavior at or above T g can be expected being observed in this case because the character of the stress relaxation in a wide temperature range is dictated above all by the deformation rates employed locally to the adjacent network-forming matrix. Since the ion migration occurs on the picosecond time scale, the primary rearrangement of the glass network adjacent to an ionic site occurs at rates orders of magnitude higher than those of the critical minimum values, so the matrix demonstrates brittle–elastic response to the arising strain even at temperatures well above T g, which explains, among other things, why mixed alkali effect is observable in glass melts.

Mixed Mobile Ion Effect and Cooperative Motions in Silver-Sodium Phosphate Glasses

The conduction pathways and the extraordinary weak mixed mobile ion effect (MMIE) in AgxNa1-xPO3 glasses have been investigated by bond-valence analysis of reverse Monte Carlo produced structural models. We find that the MMIE is suppressed in this system due to a common cooperative hopping process, where both Ag and Na participate. This finding is in strong contrast to glass systems exhibiting a pronounced MMIE, where the two types of mobile ions have distinctly different conduction pathways and the M ions tend to block the pathways for the N ions and vice versa.

Structure of AgxNa1−xPO3 glasses by neutron diffraction and reverse Monte Carlo modelling

We have performed structural studies of mixed mobile ion phosphate glassesAgxNa1−xPO3 using diffraction experiments and reverse Monte Carlo simulations. This glass system isparticularly interesting as a model system for investigations of the mixed mobile ion effect,due to its anomalously low magnitude in the system. As for previously studiedmixed alkali phosphate glasses, with a much more pronounced mixed mobile ioneffect, we find no substantial structural alterations of the phosphorous–oxygennetwork and the local coordination of the mobile cations. Furthermore, the mobileAg+ and Na+ ions are randomly mixed with no detectable preference for either similar or dissimilar pairsof cations. However, in contrast to mixed mobile ion systems with a very pronouncedmixed mobile ion effect, the two types of mobile ions have, in this case, verysimilar local environments. For all the studied glass compositions the averageAg–O and Na–O distances in the first coordination shell are determined to be2.5 ± 0.1 and 2.5 ± 0.1 Å, and the corresponding average coordination numbers are approximately 3.2 and 3.7, respectively.The similar local coordinations of the two types of mobile ions suggests that the energy mismatch fora Na+ ion to occupy a site that previously has been occupied by aAg+ ion (and vice versa) is low, and that this low energy mismatch is responsible for theanomalously weak mixed mobile ion effect.

Defect model for the mixed mobile ion effect

This paper presents a new defect model for the mixed mobile ion effect. The essential physical concept involved is that simultaneous migration of two unlike mobile ions in mixed ionic glass is accompanied by expansion or contraction of the guest-occupied sites with distortion of surrounding glass matrix; in many cases, an intensity of the local stresses in glass matrix surrounding ionic sites occupied by foreign ions is much greater than, or at least comparable to the glass network binding energy. Hence, when the stress exceeds the breaking threshold, relaxation occurs almost immediately via the rupture of the bonds in the nearest glass matrix with generation of pairs of intrinsic structural defects. The specificity of the mechanism of defect generation leads to the clustering of negatively charged defects, so that rearranged sites act as high energy anion traps in glass matrix. This results in the immobilization of almost all minority mobile species and part of majority mobile species, so mixed mobile ion glass behaves as single mobile ion glass of much lower concentration of charge carriers. Generation of defects leads also to the depolymerization of glass network, which in turn results in the reduction of the glass viscosity and Tg as well as in the compaction of glass structure (thermometer effect). In the spectra of mechanical losses of mixed alkali glasses it reflects as a shift of the maximum in mechanical losses corresponding to the glass transition to lower temperatures, and the dramatic increase of the maximum corresponding to the movement of non-bridging oxygens (so-called mixed alkali peak). The magnitude of the mixed mobile ion effect is defined by the size mismatch of unlike mobile ions, their total and relative concentrations, the binding energy of the glass-forming network, and temperature. Although the proposed model is based upon the exploration of alkali silicate glass-forming system, the approach developed here can be easily adopted to other mixed ionic systems such as crystalline and even liquid ionic conductors.

The mixed alkali effect in ionically conducting glasses revisited: A study by molecular dynamics simulation

When more than two kinds of mobile ions are mixed in ionic conducting glasses and crystals, there is a non-linear decrease of the transport coefficients of either type of ion. This phenomenon is known as the mixed mobile ion effect or Mixed Alkali Effect (MAE), and remains an unsolved problem. We use molecular dynamics simulation to study the complex ion dynamics in ionically conducting glasses including the MAE. In the mixed alkali lithium-potassium silicate glasses and related systems, a distinct part of the van Hove functions reveals that jumps from one kind of site to another are suppressed. Although, consensus for the existence of preferential jump paths for each kind of mobile ions seems to have been reached amongst researchers, the role of network formers and the number of unoccupied ion sites remain controversial in explaining the MAE. In principle, these factors when incorporated into a theory can generate the MAE, but in reality they are not essential for a viable explanation of the ion dynamics and the MAE. Instead, dynamical heterogeneity and "cooperativity blockage" originating from ion-ion interaction and correlation are fundamental for the observed ion dynamics and the MAE. Suppression of long range motion with increased back-correlated motions is shown to be a cause of the large decrease of the diffusivity especially in dilute foreign alkali regions. Support for our conclusion also comes from the fact that these features of ion dynamics are common to other ionic conductors, which have no glassy networks, and yet they all exhibit the MAE.

Ion dynamics and mixed mobile ion effect in fluoride glasses

We report the ionic relaxation and mixed mobile ion effect in 50ZrF4−10BaF2−10YF3−(30−x)LiF−xNaF fluoride glass series, where fluorine anions participate in the diffusion process in addition to alkali cations, unlike mixed alkali oxide glasses and crystals. By analyzing the ion dynamics in the framework of a power-law model as well as modulus formalism we have observed mixed mobile ion effect in the dc conductivity and its activation energy, the crossover frequency and its activation energy, the conductivity relaxation frequency and its activation energy, and also in the decoupling index. We have correlated these phenomena with the fractal dimension of the conduction pathways in the mixed alkali fluoride glasses compared to the single alkali glasses. We have shown that the relaxation dynamics in mixed alkali fluoride glasses is independent of temperature but dependent on glass composition.

Mixed mobile ion effect in fluorozincate glasses

The mixed mobile ion effect has been investigated for the first time in zinc fluoride glasseswhere in addition to alkali cations fluorine anions also participate in the diffusion process,unlike mixed alkali oxide glasses. The minimum in the conductivity, conductivity relaxationfrequency, crossover frequency and decoupling index indicates the existence of the mixedmobile ion effect in these fluoride glasses. It has been observed that the non-exponentialparameter and the frequency exponent are independent of temperature. It has beenestablished that alkali ions and fluorine anions exhibit lower dimensionality of theconduction pathways in mixed alkali zinc fluoride glasses than that in the single alkalilithium based zinc fluoride glasses while they are migrating. From the scaling of theconductivity spectra, it has been established that the relaxation dynamics inmixed alkali zinc fluoride glasses is independent of temperature and composition.

Structural properties determining the ionic conductivity ofCsI-dopedAgPO3glasses

The conductivity and structure of ${(\mathrm{CsI})}_{x}\text{\ensuremath{-}}{({\mathrm{AgPO}}_{3})}_{1\ensuremath{-}x}$ glasses, where $0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.2$, were investigated by means of dielectric spectroscopy, x-ray and neutron diffraction, and reverse Monte Carlo modeling. Evidence was found for a partial dissociation of $\mathrm{Ag}$ ions from oxygen sites into iodine-rich environments upon addition of $\mathrm{CsI}$. A similar dissociation effect, although stronger, has previously been found in ${\mathrm{PbI}}_{2}$-doped ${\mathrm{AgPO}}_{3}$ glasses, where it, together with network expansion, was considered to cause a much higher dc conductivity of ${\mathrm{PbI}}_{2}$-doped ${\mathrm{AgPO}}_{3}$ glasses as compared to $\mathrm{AgI}$-doped ${\mathrm{AgPO}}_{3}$ glasses [Phys. Rev. B 60, 12 023 (1999)]. However, the dc conductivity is much lower in the present $\mathrm{CsI}$-doped glasses than in ${\mathrm{Pbl}}_{2}$-doped glasses. This is explained on the basis that the conductivity in salt-doped ${\mathrm{AgPO}}_{3}$ is determined by three effects: (i) network expansion, (ii) partial $\mathrm{Ag}$ dissociation, and (iii) a mixed mobile ion effect. The last effect, which reduces the conductivity, is present when the salt cations, here cesium ions, are mobile.

Mixed mobile ion effect in fluoride glasses

Certain ionic materials containing dissimilar mobile cations exhibit the nonlinear behavior of diffusion-related properties, called the mixed mobile ion effect. In these materials only cations participate in the diffusion process. In this paper we report on the mixed mobile ion effect in fluoride glasses, where anions also participate in the diffusion processes in addition to cations, unlike mixed alkali oxide glasses and crystals. We have provided several pieces of evidence in favor of this effect in fluoride glasses. This phenomenon was associated with the low dimensionality of the diffusion pathways in the mixed alkali fluoride glasses compared to single alkali glasses.

Ionic conduction and dielectric relaxation in Ag +/Na + ion-exchanged aluminosilicate glasses: mixed mobile ion effect and KWW relaxation

Ag +/Na + ion-exchanged aluminosilicate glasses with uniform concentration profiles were prepared, and their electrical conductivities were investigated as functions of the ion-exchange ratio and the initial glass compositions. In the case of the ion-exchanged glasses of x20Ag 2O–(1− x)20Na 2O–10Al 2O 3–70SiO 2 in mol%, the conductivity, σ, and its activation energy, E σ , showed a minimum and a maximum at the same ion-exchange ratio x=0.3, respectively, and the mixed mobile ion effect (MMIE) was observed. The fully ion-exchanged sample attained σ=3.5×10 −5 S/cm at 200 °C, which was 1.5 orders of magnitude larger than that of initial glass. In the case of x25Ag 2O–(1− x)25Na 2O–25Al 2O 3–50SiO 2, the mixed mobile ion effect was also observed at x=0.5. The maximum conductivity of 2×10 −4 S/cm at 200 °C was obtained in the fully ion-exchanged glass sample. The electric relaxation analysis was also conducted on both systems, and Kohlrausch–Williams–Watts (KWW) fractional exponent β was obtained as a function of x. The decrease of β was observed near x≈0.3 in the former system, while that of the later system was independent of the ion-exchange ratio. Based on the structural analysis results, the observed behaviors were investigated from the point of view of the occupation of Ag + ions on the non-bridging oxygen-site (NBO-site) and the charge compensation-site (CC-site) of AlO 4 tetrahedral unit.

Electrical conductivity and conductivity relaxation in mixed alkali fluoride glasses

We report the electrical conductivity and the conductivity relaxation of the mixed alkali fluoride glasses in the system 50ZrF 4–20BaF 2–5YF 3–5AlF 3–(20− x)LiF– xNaF (0≤ x≤20) in the frequency range from 10 Hz to 2 MHz and the temperature range from 300 to 473 K. We have analyzed the electrical data in the framework of the conductivity as well as the modulus formalism. We have observed the mixed mobile ion effect in the conductivity and the conductivity relaxation in these mixed alkali fluoride glasses. The characteristic relaxation frequency obtained from the conductivity formalism and the conductivity relaxation time obtained from the modulus formalism exhibit minimum at different relative concentration.

Conductivity relaxation in mixed alkali fluorideglasses

We have reported the electrical conductivity and theconductivity relaxation in fluoride glasses in the system40ZrF4-20BaF2-10YF3-(30-x)LiF-xNaF;0⩽x⩽30. We have observed a mixed mobile ioneffect in these mixed alkali fluoride glasses. Using modulus formalism we have shown that the conductivity relaxation alsoexhibits the mixed mobile ion effect as does the dc conductivity. Wehave observed that the relaxation mechanism is independent oftemperature but dependent on the composition.

Experimental insight into the mixed mobile ion effect in glasses

The structures of ion conducting mixed-alkali metaphosphate glasses (A 2O) x –(B 2O) 1− x –P 2O 5 (A,B=Li,Na,Rb) have been examined by neutron diffraction and Raman spectroscopy. The results show that the short range order of the phosphorous–oxygen network is almost independent of the composition. The length-scale of the intermediate range order correlations increases with increasing size of the cation. For all the investigated compositions the nearest Li–O, Na–O and Rb–O distances have been estimated from the atomic pair correlation functions to be 2.0±0.1, 2.35±0.1 (Na–O I), 2.6±0.1 (Na–O II) and 2.9±0.1 Å, and the corresponding average coordination numbers are approximately 4, 3 (I)+2.5 (II) and 5, respectively. Thus, the cation environments are distinctly different for Li +, Na + and Rb + and each of them remain the same for all compositions within experimental errors. The alkali ions are quasi-uniformly distributed and we were not able to observe any significant preference for either similar or dissimilar pairs. This implies that the mixed-alkali effect can be qualitatively understood on a purely structural basis. The A sites are energetically unfavourable to the B + ions (and vice versa) and jumps to dissimilar sites are then unlikely to occur. Thus, the A sites will have the tendency of blocking the pathways for the B + ions and vice versa.