We study the switching characteristics of nanoscale junctions between a metallic tip and a silver film covered by a thin Ag2S ionic conductor layer. Resistive switching phenomena are studied on samples of various Ag2S layer thicknesses. Metallic and semiconductor behavior are distinguished by current-voltage characteristics measured at room temperature and at 4.2 K.

Interfacial polarization in electrolytes or other ionic media is a well-known phenomenon in connection with the relative surface potential difference. The created space charge affects the distribution of charge carriers in an electrolyte itself similarly to the field effects in semiconductors. This results in a number of secondary effects, from dielectrophoresis to the varied conductivity of the media. Some of these effects, including dielectrophoresis, and electric field sensing in the electrolytes, are analyzed analytically, modeled numerically, and evaluated experimentally. The physical nature of the thermoelectric effect in gels and a totally ionic field effect transistor is revealed, and the correspondence to experimental data is demonstrated.

Linking the bond valence mismatch to the absolute energy scale, a generally applicable Morse-type force-field is developed and applied to study ion conduction in mixed conducting solids using both an energy landscape approach and molecular dynamics (MD) simulations. Exploring strategies to enhance the power performance of safe low cost lithium ion battery cathode materials, amblygonite-type “high voltage” cathode materials LiVPO4F and LiFeSO4F are used as examples. The amblygonite-type structure exhibits channels for low-energy migration in combination with moderate energy thresholds for "back-up" pathways in perpendicular directions mitigating the effects of channel blocking in mixed conductors with strictly one-dimensional Li+ motion.

The perovskite Ba0.5Sr0.5Co0.8Fe0.2O3-d (BSCF 5582) has attracted great interest as an oxygen reduction catalyst for solid oxide fuel cells and as an oxygen permeation membrane material. Mixed ionic and electronic conductivity is essential to the high catalytic activity it exhibits, however its electronic behavior and overall defect chemistry are not well understood. The related material SrCo0.9Nb0.1O3-d (SCN 091) is another promising composition that may have comparable performance, but with defect chemistry that is simpler to study. From a combination of thermogravimetric, impedance, and diffraction measurements we find SCN 091 to exhibit somewhat smaller oxygen nonstoichiometry, five times higher electronic conductivity, lower enthalpy of hole migration, and greater structural stability than BSCF 5582. We also observe that the enthalpy of hole migration in such materials tends to increase as oxygen content decreases; the origins of this behavior are unclear.

Hetero-interface between two oxides sometimes forms a dipole layer which is experimentally observable macroscopically, as an electric potential barrier at the interface. Investigation of the flatband voltage shift of the metal-insulator-semiconductor capacitors with bilayer oxides as the insulator is suitable to characterize the dipole formation at the interface of two oxides. A model to explain the driving force to form the dipole is discussed by taking account of the areal density difference of oxygen atoms at the interface, which should be a guideline to predict both the direction and magnitude of the interface dipoles. Based on this model the requirement for the oxides to form the dipoles is also discussed.

We investigate the electronic structure of interstitial Li and Li vacancy in Li7P3S11 by first principles calculations. We find that Li7P3S11 is a good insulator with a wide band gap of 3.5 eV. We find that the Li vacancy and interstitial Li+ ion do not introduce states in the band gap hence they do not deteriorate the electronic properties of Li7P3S11. The calculated formation energies of Li vacancies are much larger than those of Li interstitials, indicating that the ion conductivity may arise from the migration of interstitial Li.

Yttria-stabilized zirconia’s high oxygen diffusivity and corresponding high ionic conductivity, and its structural stability over a broad range of temperatures, have made the material of interest for use in a number of applications, for example, as solid electrolytes in fuel cells. At low concentrations, the stabilizing yttria also serves to increase the oxygen diffusivity through the presence of corresponding oxygen vacancies, needed to maintain charge neutrality. At higher yttria concentration, however, diffusivity is impeded by the larger number of relatively high energy migration barriers associated with yttrium cations. In addition, there is evidence that oxygen vacancies preferentially occupy nearest-neighbor sites around either dopant or Zr cations, further affecting vacancy diffusion. We present the results of ab initio calculations that indicate that it is energetically favorable for oxygen vacancies to occupy nearest-neighbor sites adjacent to Y ions, and that the presence of vacancies near either species of cation lowers the migration barriers. Kinetic Monte Carlo results from simulations incorporating this effect are presented and compared with results from simulations in which the effect is not present.

Lithium ion conducting argyrodite-type Li6PS5X (X = Cl, Br, I) compounds were prepared using mechanical milling followed by annealing. XRD characterization reveals the formation and growth of Li6PS5X crystals in samples under varying annealing conditions. Temperature dependent XRD data showed the monotonic increase of lattice constant within the range of study. For Li6PS5Cl and Li6PS5Br an ionic conductivity of the order of 10-3 S/cm is reached at room temperature, which is close to the Li mobility in conventional liquid electrolytes and well suitable for all-solid-state safe electrochemical energy storage devices. Bond valence analysis of Li ion migration paths for the argyrodites showed the formation of low energy pathway cages around halide ion for Li6PS5Cl, around the sulfide ion for Li6PS5I. For higher activation energies these cages are interconnected to form a 3-D pathway network. In the case of Li6PS5Br cages around Cl and Br require about the same activation energy.

In nano-crystalline ceramics, the grain boundary volume fraction is large relative to that in micro-crystalline materials and can therefore become the dominant factor in determining its electrical, chemical, and mechanical properties. Reduced enthalpies of defect formation for nanocrystalline Pr0.1Ce0.9O2-δ , derived from thermo-gravimetric and impedance spectroscopy measurements, are reported. In addition, observations of cerium carbonate formation on nanoporous materials and implications for thermo-gravimetric analysis are discussed.