The modelling of electro-diffusion in the multicomponent system in open space and time domains has been only recently addressed and made numerous applications in biology, fuel cells, electrochemical sensors and reference electrodes possible. In this work we show the numerical simulations of electrical potential over time and resulting electrochemical impedance spectra of ion-selective membrane electrodes (ISE’s). The numerical results are obtained by use of the coupled Nernst-Planck, Poisson and continuity equations (forming the NPP model). The equations are solved by means of the finite difference method, the Rosenbrock solver with the use of Matlab (by MathWorks) platform. The potential-time response of the ISEs in open- and closed-circuit conditions as a function of varying heterogeneous rate constants, ionic concentrations and membrane thickness are computed. The potential-time response to small-current perturbation is applied for simulations of the impedance spectra. The results obtained show that the membrane with Nernstian response presents only one capacitive arc in the impedance spectra, related to conductivity and dielectric properties of the membrane material. Non-Nernstian behaviour is related to slow ionic transport through the membrane|solution interfaces and is manifested by the appearance of an additional (capacitive) arc between the highfrequency bulk and the low-frequency (Warburg) arcs. The presented approach directly relates the diffusivities in the membrane and the interface properties (heterogeneous rate constants determining the transport across interfaces) to the characteristic properties of the impedance spectra (characteristic radial frequencies). It is concluded that the Matlab platform allows solving the NPP problem and simulating the non-linear effects in electrodiffusion in a convenient way.

Long-range Li diffusion parameters of amorphous LiNbO3 are probed by 7Li two-time spin-alignment echo NMR spectroscopy which is sensitive to slow Li dynamics. The jump rates which were extracted from the spin-alignment echo decay curves exhibit Arrhenius behaviour between 293 K and 413 K. The activation energy (0.41(1)eV) is in good agreement with that of the high-temperature flank of the 7Li NMR spinlattice relaxation rate peak. The latter was predicted to be about 0.4 eV when taking into account the frequency dependence of the corresponding spin-lattice relaxation rates on the low-T flank (see Wilkening et al., Phys. Chem. Chem. Phys. 4 (2002) 3246). Previous measurements of the spin-lattice relaxation rate had to be restricted to temperatures below 450 K in order to avoid crystallization of the material. Thus, only the low-temperature flank of the diffusion induced spin-lattice relaxation rate peak had been accessible yielding information about short-range Li diffusion.

High temperature properties such as electrical conductivity (σ) and resonance behaviour of stoichiometric lithium niobate (LiNbO3) are determined in the temperature range from 20 to 950 °C. The activation energy of the conductivity is found to be 0.9 and 1.7 eV in the temperature range from 500 to 750 °C and from 800 to 950 °C, respectively. During thermal treatments in ambient air up to 950 °C and back, the conductivity remains unchanged at a given temperature, i.e., the crystal is stable under these conditions. The oxygen partial pressure (pO2) dependence of the conductivity shows two distinct ranges. At 750 °C, the property remains unchanged down to 10−15 bar. Below 10−15 bar, the conductivity increases according to σ ~ (pO2)−1/5. Z-cut LiNbO3 plates can be excited to thickness mode vibrations up to at least 900 °C. At this temperature, the quality factor Q is found to be between 30 and 100. As for changes of the conductivity, a decrease of the resonance frequency is observed below 10−15 bar indicating a correlation of both properties. In order to evaluate the lithium evaporation, the crystals are tempered at 900 °C in ambient air for 24 h. A depth profile of the constituents does not indicate lithium loss within the accuracy of the secondary ion mass spectroscopy. The preliminary results underline the potential of stoichiometric LiNbO3 for high-temperature applications and justify its closer investigation.

Zirconia powders doped with different amounts of dopants (CeO2, Gd2O3, and CaO) were synthesized by a citrate technique. X-ray diffraction for samples sintered at 1500 °C revealed that the zirconia ceramics were stabilized in the cubic phase above 12 mole % CaO and 10 mole % Gd2O3, while tetragonal zirconia is obtained above 15 mole % CeO2. Relative densities up to 99.5% were obtained. The effect of dopant concentration on the lattice parameter, average crystallite size, microstrain was studied. The cubic lattice parameter increases nearly linearly with increasing the concentration in case of CaO and Gd2O3. The tetragonal lattice parameters at and ct increase nearly linearly with increasing the concentration of CeO2. The average crystallite size was found to be larger than 600 nm for the samples investigated.

Cation doped zirconium oxynitrides (for example zirconium oxide doped with yttrium oxide and nitrogen, \''YZrON\''), having a fluorite-based structure, are suggested to have fairly high nitrogen diffusivity, besides their high oxygen mobility. In the present work, the tracer-diffusion of nitrogen and oxygen was measured in single crystalline \''YZrON\''. Results are compared to the migration pathways and migration enthalpies of nitrogen and oxygen ions as determined by elastic neutron diffraction studies. Excellent agreement of the measured activation enthalpies of nitrogen diffusion (about 2 eV) and oxygen diffusion (about 1 eV) determined by the two methods is found.

Amorphous precursor derived ceramics with the composition Si26C41N33 were isothermally annealed at 1500 °C for 5 minutes up to 190 minutes. Two series of measurements were carried out: one at a nitrogen partial pressure of 1 bar and one at a nitrogen partial pressure of 1 mbar. Small angle X-ray scattering was used to determine the diameter of the amorphous domains. The Guinier radius was found to vary from 9.5 Å to 13 Å irrespective of the partial pressure of nitrogen. This finding is quite surprising since crystallization of this material strongly depends on the partial pressure of nitrogen.

In the present work the effect of compressive stress on self-diffusion of Fe in nanocrystalline FeN(Zr) alloys has been investigated. Two different types of Fe64N26Zr10 samples, one without applied stress and another with applied compressive stress of 42 GPa, were deposited under identical conditions using magnetron sputtering. The stress has been applied to the sample by bending the substrate during the deposition using a three point bending device. The self-diffusivities of Fe were determined by measuring the broadening of 57Fe marker layers by Secondary Ion Mass Spectrometry after annealing at 443 K, 483 K and 523 K for 1 hour. The activation energy and preexponential factor for Fe diffusion is comparatively higher in the stressed sample. The higher activation energy might be due to the fact that the system transforms into a more dense state when compressive stress is applied.

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