Conductivity In Ionic Conductors Research Articles

Dynamic Metal-Ligand Coordination-Assisted Ionogels for Deformable Alternating Current Electroluminescent Devices.

Overcoming the trade-off between the mechanical robustness and conductivity of ionic conductors is a crucial challenge for deformable ionotronics. In this work, we propose a simple but effective gelation strategy for selectively improving the mechanical robustness of ionogels without compromising their ionic conductivity. To achieve this, we introduce dynamic metal-ligand coordination chemistry into the ionic liquid (IL)-insoluble domains of a physically crosslinked ionogel network structure. As a result, the overall mechanical property is remarkably improved with the aid of additional chemical crosslinking. This strategy does not require any additional heat/light (UV) treatments to induce chemical crosslinking. The homogeneous physically/chemically dual crosslinked ionogel films can be readily obtained by simply casting a solution containing Ni2+ sources, copolymer gelators, and ILs. The effects of adjusting fundamental parameters on the ionogel properties are investigated systematically. The optimized mechanically robust and highly conductive ionogels are successfully employed as deformable ionic electrodes in alternating-current electroluminescent displays, indicating their high practicality. Overall, these results validate that exploiting metal-ligand coordination dynamic bonding is an extremely straightforward strategy for selectively improving the mechanical characteristics of conductive ionogels, which are promising platforms for deformable ionotronics.

Fabrication of ZrO2(MgO)/CaAl2O4+CaAl4O7 Bilayer Structure Used for Sulfur Sensor by Laser Cladding

The ZrO2(MgO)/CaAl2O4+CaAl4O7 bilayer structure used for sulfur sensor was fabricated by the laser powder cladding (LPC) method using the MgO partially stabilized zirconia (2.7 wt% MgO-PSZ) as the substrate and the CaAl2O4 + CaAl4O7 composites as the coating material. The microstructure, phase composition and ionic conductivity of this bilayer structure were investigated for better application in the sulfur determination. The results indicated that the structure of the coating was dense and well-distributed with a thickness of 100 μm. The ionic conductivity of the ZrO2(MgO)/CaAl2O4+CaAl4O7 bilayer structure was up to 2.06 × 10−3 S·cm−1 at 850 °C that met the required ionic conductivity of ionic conductor for solid electrolyte sulfur sensor. Furthermore, the sulfur sensor Mo|Cr+Cr2O3| ZrO2(MgO)| CaAl2O4+CaAl4O7|[S]Fe| Mo was assembled used this bilayer structure and tested in carbon-saturated liquid iron at 1773 K and 1823 K. The stability and reproducibility of the sulfur sensor were satisfactory and could be used for sulfur determination in the liquid iron.

Analytical approximation for the frequency dependent conductivity in ionic conductors

Solid ion conductors exhibit a frequency dependent conductivity that is well described by the coupling model, which includes stretched-exponential relaxation to describe ion-ion interactions. As yet, materials characterization taking this frequency dependence into account is inaccessible to non-experts in numerical analysis, since it requires computer-assisted evaluation of complex integrals. On the other hand, commonly used impedance models lead to inaccurate results and have limited applicability. The purpose of this article is to provide an approximation to the coupling model in terms of elemental functions. With fits to multiple reference data sets we demonstrate the advantages of our approach over commonly used methods. We then apply our model to the characterization of polyethylene oxide based electrolytes, used in all-solid-state batteries, and show that such a case could not be accurately studied with standard impedance models.

Impact of particle size on conductivity and storage capacity as derived from the core–space charge model

The impact of interfaces on variety of materials properties scales with the density of interfaces within a material. This statement holds true independent of the specific interfacial mechanism, as long as the density of interfaces is rather low. If the spacing between interfaces is being further reduced, interesting non-trivial effects are expected and have also been observed. In this paper, the ionic conductivity in ionic conductors and the storage capacity (non-stoichiometry) of mixed conductors as a function of size are considered. The discussion is based on the core–space charge model in which we assume that only the core of an interface exhibits its own defect energetics, while the energetics of the space charge layers remain unaltered (compared to the bulk). It is shown that in the case of Schottky profiles anomalous conductivity effects are predicted. As regards the non-stoichiometry effects, it is demonstrated that at sizes small compared to the Debye length the difference between a composite consisting of an ionic and an electronic conductor and a «true» mixed conductor becomes blurred. The latter effect has recently been detected in the field of Li-batteries and is here commented on.

The crossover from the near constant loss to ion hopping ac conductivity in ionic conductors: the crossover times

We show how the near constant loss (NCL) crosses over to cooperative ion hopping from extensive dielectric measurements of the glass-forming molten salt 0.4Ca(NO 3) 2–0.6KNO 3 (CKN) of Lunkenheimer and co-workers at temperatures below and above the glass transition temperature. The NCL ends when time exceeds t x1 and cooperative hopping becomes prominent beyond t x2 . The crossover, occurring over the time region t x1 < t< t x2 , is not sharp but t x1 and t x2 are not far from each other in order of magnitude. At most temperatures the primitive relaxation time τ 0 of an ion in the coupling model calculated from the experimental data lies inside the crossover region and is not much shorter than t x2 Since τ 0 is the relaxation time of a caged ion in a potential well to overcome the energy barrier by thermal activation, the findings here support the proposal that the origin of the NCL comes from the very slow decay with time of the cage confining the ion in its potential well. A simple theoretical model of a caged particle that has its cage decaying very slowly with time is solved numerically and a NCL over many decades of frequency is reproduced.

Test of universal scaling of ac conductivity in ionic conductors

Electrical relaxation data of crystalline yttria-stabilized zirconia are used to analyze the permittivity change observed in the spectra of the real part of the permittivity in ionic conducting materials. It is found that this permittivity change is independent of both temperature and mobile-ion concentration, and it is determined solely by the degree of interaction among ions in the relaxation process. This finding is at odds with an expression for the permittivity change in the framework of a proposed universal ac conductivity scaling law for glassy ionic conductors. On the other hand, not only the total permitivity change, but also the particular frequency dependence of the permittivity spectra is found to be consistent with the analysis of electrical relaxation in terms of the electric modulus. The results of this work give further support to the use of the electric modulus in describing electrical relaxation in ionic conductors.

The characteristic frequencies for ionic conduction in 12 mol.% Y2O3 doped ZrO2

DC conductivity in ionic conductors is proportional to the hopping rate of the charge carriers. The hopping of the charge carriers can result in a dielectric loss peak and the DC conductivity is also proportional to the loss peak frequency. In the present study, the AC conductivity of 12 mol.% Y 2 O 3 doped ZrO 2 has been measured and the relationship between the hopping frequencies characteristic of the AC conductivities and dielectric loss peak frequencies has been examined. In addition, the peak frequencies in the complex impedance plane were also measured, to compare with the hopping frequencies. It has been demonstrated that two sample constants can be used to connect the three frequencies. It is suggested that the three frequencies are a consequence of a common phenomena and that all result from the hopping process of the charge carriers.

Particle-size effect on the percolation and conductivity of dispersed ionic conductors: A random sequential packing model.

The particle-size effect on the percolation and conductivity of ionic conductors containing a dispersed second phase is investigated on the generalized random resistor networks model. A random sequential packing model different from the one used by Roman and Yussouff is proposed, and by computer simulations we find that there is a maximum critical particle size above which the second critical concentration ${\mathit{p}}_{\mathit{c}}^{\mathrm{\ensuremath{''}}}$ at which the conductor-insulator transition takes place, will disappear. The first critical concentration ${\mathit{p}}_{\mathit{c}}^{\ensuremath{'}}$ at which the interface percolation transition occurs may also disappear above the critical particle size. The particle-size effect on the conductivity property of the present model is studied with a powerful and efficient Y-\ensuremath{\nabla} transformation algorithm, and the numerical results are in good agreement with experiment results and previous conclusion. \textcopyright{} 1996 The American Physical Society.

Conductivity of dispersed ionic conductors: A percolation model with two critical points.

The conductivity of ionic conductors containing a dispersed insulating second phase is investigated from the point of view of percolation theory. Using Monte Carlo simulations, we study a resistor model in two and three dimensions, which emphasizes the role of an enhanced interface conductivity. The existence of two critical concentrations ${p}_{c}^{\mathcal{'}}$ and ${p}_{c}^{2\mathrm{sprime}}$ of an insulating phase leads to a characteristic dependence of the overall conductivity on composition which is in remarkable agreement with experiment. Detailed calculations near the two thresholds ${p}_{c}^{\mathcal{'}}$ and ${p}_{c}^{2\mathrm{sprime}}$ yield critical properties in accord with random superconducting and random resistor networks. The question of a possible experimental verification of those critical properties is also discussed.