Total ionic conductivity

However, in the case of the perovskite even the application of sintering temperatures as high as 1200 °C did not result in a higher overall ionic conductivity. Since the total ionic conductivity is two orders of magnitude lower than the bulk conductivity in polycrystalline Li0 34La05] Ti 0294, an improvement by way of the preparation route is necessary rather than changes in the lattice by the addition of dopants,... 

The above theory can also be applied to account for the concentration dependence of transport numbers, especially in dilute solutions. Since the transport number can be defined as a ratio of the equivalent conductance of the given ion to the total ionic conductance (equation (6.7.6)), it is clear that a non-linear relationship can be derived describing the concentration dependence using equations (6.9.23) and (6.9.24). 

Because of the resistance to ion flow at the electrode-electrolyte interface, normal measurement of total ionic conductivity is not possible in polymer electrolytes. In order to overcome this problem the conductivity measurements are carried out by the ac impedance spectroscopy method, which minimizes the effects of cell polarization. The measurements are often made with the electrolyte sandwiched between a pair of electrochemically inert electrodes made of platinum or stainless steel. The detailed methodology of impedance spectroscopy is reviewed thoroughly elsewhere [45-47]. 

Attempts to obtain transport number information by various methods such as pulsed field gradient NMR [62], radio tracer diffusion [77], and potentiostat-ic polarization technique [46] have suggested that both cation and anion mobilities are important for the total ionic conductivity seen. In general, however, the nature of charge carriers in polymer electrolytes is quite complex and ion aggregates such as triple ions have been implicated in conductivity [78-79]. 

Molar ionic conductivities. At infinite dilution, each ionic species present contributes a fixed amount to the total ionic conductivity, regardless of the nature of any other ions present. This means that the total conductivity of a sufficiently dilute solution is given by the sum of the individual ionic conductivities of the i different ionic species present [Eq. (D.7)] ... 

Transport numbers vary with the nature of the dissolved salt and of the solution as well as with concentration of the electrolyte. Transport numbers do change with concentration in a solution of a single salt, but only slightly. However, because the transport number of an ion is the fraction of the total ionic conductance due to that ion, the transport number of any particular ion or ions can be reduced to virtually zero by the addition to the solution of a large concentration of some salt that does not contain them. Electrochemists often make use of this technique. 

La-doped ceria. A correlation between synthesis process, nanodomain size, and total ionic conductivity was observed for Yb, Ho, and Dy -doped ceria. Furthermore, recent results question the established solubility limits of rare-earth cations in ceria. Although the lattice parameter of ceria increases with La doping up to 40 mol% LaOi the true solubility turns out to be below 20 mol% LaOj 5 as evidenced from the formation of C-LagOg after annealing Ceo.sLao.aOi g at 1000 °C for 7 days. Pronounced deviations from Vegard s law have been consistently observed for the lattice constant of Gd-doped ceria. These may be rationalized by the formation of C-GdgOg domains within the ceria fluorite lattice. ... 

The electrolytic domain ti> 0.99) of doped ceria is limited at low PO2 due to the onset of electronic conductivity on reduction of Ce. The low p02 limit of the electrolytic domain depends on dopant type and doping level, and shifts to higher pOg with increasing temperature. The width of the electrolytic domain is maximized for 10-20 mol% Gd- or Sm-doped ceria, °° due to the optimized total ionic conductivity achieved in these compounds. The low pOg limit of these compounds shifts from ca. 10 atm at 400 °G and ca. 10" atm at 600 °C to ca. 10 atm at 800 For comparison, the... 

The behavior of the anion receptor TPEPB in a 1 M LiCl04 electrolyte in EC/DMC (1/2.5 v/v) was studied by Lee et al. [425]. The transference number of the lithium cation was enhanced by increasing the TPFPB content from 0.22 (0 M TPFPB) to 0.55 (0.1 M TPFPB), measured by the potentiostatic polarization method of Bruce and Vincent (see Section 17.4.6.4). The total ionic conductivity decreased due to the decreasing anionic conductivity, but the cationic conductivity increased. The interaction between TPFPB and Cl04, resulting in formation of a complex and advanced dissociation of LiCl04, was shown by FTIR analysis. 

In the case of granular LLTO, the ionic conductivity increases by replacing the titanium with a small amount of Al. On the other hand, the addition of sodium will decrease the conductivity. The substitution of oxygen with fluorine does not significantly improve the conductivity. Addition of Si into Lig sLao sTi03 increases the total ionic conductivity since Si affects the ion movement along the particle boundary. 

A feature of the behaviour of such concentrated systems is the preponderance of ion pairs and triple ions. The ionic transport then includes contributions from cations such as M2X+ and anions such as MX2. Most techniques for determining the individual conductivities of different species in fact only discriminate between two classes those that are reversible at a given non-blocking electrode and those that are not. If the test cell is configured so that the contribution of the cations to the total ionic conductivity can be determined, then the cationic transference number, x+, can be obtained. This may be defined as ... 

The total ionic conductivity is an important characterization parameter which has been used as the criterion for possible application in devices. A PE intended for use in diverse electrochemical applications must have adequate ionic conductivity, together with negligible electronic conductivity if self-discharge on standing is to be avoided. A PE is considered to be a promising candidate for commercial application if its ionic conductivity is as high as 10 S cm at room temperature. ... 

Typically the total ionic conductivity of the di-ureasils discussed here was measured by placing the sample between gold blocking electrodes, along the so-called electrode/di-ureasiUelectrode assembly, which was secured in a suitable constant-volume support, to form a symmetrical cell. 

The conductivity isotherms derived from conductivity measurements revealed the presence of a maximum conductivity for the electrolyte system located in the composition interval 8 < n < 10. Ionic conductivity in this hybrid electrolyte increases gradually with salt content for compositions with n > 10. This parameter is generally expected to increase with the number of charge carriers, up to a limit found at about n = 8. Further increase in salt content beyond this concentration resulted in a decrease in total ionic conductivity. This observation can be explained by the formation of associated ionic species (e.g. contact ion pairs, triplets or higher multi-plets or ultimately ion aggregates) and an increased tendency for ions to form bridging interactions between adjacent polymer chains a process... 

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