Ionic Transport in Glassy Networks with High Electronic Polarizabilities: Conductivity Spectroscopic Results Indicating a Vacancy-Type Transport Mechanism

Time-Temperature Scaling of Conductivity Spectra of Organic Plastic Crystalline Conductors

Organic plastic crystalline soft matter ion conductors are interesting alternatives to liquid electrolytes in electrochemical storage devices such as lithium-ion batteries. The solvent dynamics plays a major role in determining the ion transport in plastic crystalline ion conductors. We present here an analysis of the frequency-dependent ionic conductivity of succinonitrile-based plastic crystalline ion conductors at varying salt composition (0.005 to 1 M) and temperature (-20 to 60 °C) using time-temperature superposition principle (TTSP). The main motivation of the work has been to establish comprehensive insight into the ion transport mechanism from a single method viz. impedance spectroscopy rather than employing cluster of different characterization methods probing various length and time scales. The TTSP remarkably aids in explicit identification of the extent of the roles of solvent dynamics and ion-ion interactions on the effective conductivity of the orientationally disordered plastic crystalline ion conductors.

Time-humidity-superposition principle in electrical conductivity spectra of ion-conducting polymers

We analyze the scaling properties of the ac conductivity spectra of ion-conducting polyelectrolyte complexes of different compositions. Spectra were taken at ambient temperature but at different relative humidities. For the first time, we report on a scaling principle for conductivity spectra termed "time-humidity-superposition principle" in analogy with the well-known time-temperature-superposition principle. This model-free scaling holds for different materials over several decades in frequency. It implies that the hydration is activating ion motion over short and long distances in a similar general way, a concept so far only established for thermal energy.

Mechanisms of Ion Conduction in Polyelectrolyte Multilayers and Complexes

This paper reviews the progress made in understanding of the mechanisms of ion conduction in polyelectrolyte multilayers (PEM) and polyelectrolyte complexes (PEC). The basis are experimental conductivity data obtained by impedance spectroscopy as a function of relative humidity and temperature, respectively. Mechanically stable thin films of PEM have interesting perspectives as ion conductors, however, being prepared by self-assembly, their stoichiometry and content of ionic charge carriers is unknown. Therefore PEC act as a model material with a variable stoichiometry and known ion content.

Employing poly(sodium 4-styrene sulfonate) (NaPSS) and poly(diallyldimethyl ammoniumchloride) (PDADMAC), we present conductivity spectra of dried polyelectrolyte complexes of type xNaPSS·(1-x)PDADMAC as a function of temperature and composition, respectively. The dependence of the dc conductivity is discussed along with scaling properties of the spectra. The results show that the conductivity is always determined by the sodium ions, even in PEC with an excess of PDADMAC. The ion dynamics and transport mechanisms are, however, different in PDADMAC-rich than in NaPSS-rich PEC.

PEM of different polyionic compounds are investigated in dependence on relative humidity. A general law of an exponential increase of the dc conductivity with relative humidity is found. Absolute values of the conductivity and the strength of the humidity dependence are different for different polyion materials, however, they do not depend on the type of small counterion employed in layer formation. Therefore, it is concluded that in hydrated PEM, protons are the dominant charge carriers.

For both PEM and PEC we show that the MIGRATION concept developed by Funke and co-workers can be used for describing the experimental spectra over wide ranges in frequency. This implies that forward-backward hopping motions of small ions play a vital role in solid polyelectrolyte materials. Apart from these potentially successful hops, localized motions of charged particles are found to influence the conductivity spectra as well.

Unconventional scaling of electrical conductivity spectra for PSS-PDADMAC polyelectrolyte complexes

For the first time, we analyze ac conductivity spectra of various dried ionically cross-linked polyelectrolyte complexes in terms of the time-temperature superposition principle. The temperature-dependent spectra of some complexes show scaling properties that are distinctly different from the behavior of all other ion-conducting materials reported so far, but in agreement with model predictions by Roling [B. Roling, Phys. Chem. Chem. Phys. 3, 5093 (2001).10.1039/b105094j]. We conclude that the dc conductivity of the investigated PEC is always governed by the Na+ ions, even in complexes with excess of polycations and chloride anions.

Structural integration of tellurium oxide into mixed-network-former glasses: connectivity distribution in the system NaPO(3)-TeO(2)

Sodium phosphate tellurite glasses in the system (NaPO(3))(x)(TeO(2))(1-) (x) were prepared and structurally characterized by thermal analysis, vibrational spectroscopy, X-ray photoelectron spectroscopy (XPS) and a variety of complementary solid-state nuclear magnetic resonance (NMR) techniques. Unlike the situation in other mixed-network-former glasses, the interaction between the two network formers tellurium oxide and phosphorus oxide produces no new structural units, and no sharing of the network modifier Na(2)O takes place. The glass structure can be regarded as a network of interlinked metaphosphate-type P(2) tetrahedral and TeO(4/2) antiprismatic units. The combined interpretation of the O 1s XPS data and the (31)P solid-state NMR spectra presents clear quantitative evidence for a nonstatistical connectivity distribution. Rather, the formation of homoatomic P--O--P and Te--O--Te linkages is favored over mixed P--O--Te connectivities. As a consequence of this chemical segregation effect, the spatial sodium distribution is not random, as also indicated by a detailed analysis of (31)P/(23)Na rotational echo double-resonance (REDOR) experiments.