The sintering behavior of nanocrystalline ZnO was investigated at only 250 °C. Densification was achieved by the combined effect of uniaxial pressure and the addition of water both in a Field Assisted Sintering Technology/Spark Plasma Sintering apparatus and a warm hand press with a heater holder. The final pure ZnO materials present high densities (> 90 % theoretical density) with nano-grain sizes. By measuring the shrinkage rate as a function of applied stress it was possible to identify the stress exponent related to the densification process. A value larger than one points to non-linear relationship going beyond single solid-state diffusion or liquid phase sintering. Only a low amount of water (1.7 wt.%) was needed since the process is dictated by the adsorption on the surface of the ZnO particles. Part of the adsorbed water dissociates into H + and OH -ions, which diffuse into the ZnO crystal structure, generating grain boundaries/interfaces with high defect chemistry. As characterized by Kelvin Probe Force Microscopy, and supported by impedance spectroscopy, this highly defective grain boundary area presents much higher surface energy than the bulk. This highly defective grain boundary area with high potential reduces the activation energy of the atomic diffusion, leading to sinter the compound at low temperature.

Solid polymer electrolytes (SPEs) are promising candidates for the realization of lithium metal batteries. However, the popular SPE based on poly(ethylene oxide) (PEO) reveals a "voltage noise"-failure during charge, for example, with high energy/high voltage electrodes like LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622), which can be attributed to short-circuits via penetrating Li dendrites. This failure disappears when integrating PEO-based SPE in a semi interpenetrating network, which mainly consists of PEO units, as well. In this work, it is shown that this SPE allows performance improvement via elimination of the crystalline domains without significant sacrifice of mechanical integrity. Hence, a highly amorphous SPE can be obtained by a simple increase of plasticizing Li salts, which overall is beneficial, not only for the ionic conductivity, but also the homogeneity, while remaining mechanically stable and solid in its original shape even after storage at 60 °C for 7 days. These aspects are crucial for the performance of the modified SPE as they can suppress the failure-causing Li dendrite penetration while the electrochemical aspects, that is, anodic stability, are rather unaffected by the modification and remain stable (4.6 V vs Li│Li +). Overall, this optimized SPE enables stable cycling performance in NMC622│SPE│Li cells, even at 40 °C operation temperature.

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The effect of addition of transition metal oxides on the charge transport of commercially available Gd-doped ceria (Ce 0.9 Gd 0.1 O 2-δ ) was assessed with special emphasis on the electronic partial conductivity. The samples were doped by adding 2, 4 or 6 cat% of CoO 3/4 or FeO 2/3 , or 2 mol% of the transition metal oxides V 2 O 5 , MnO 2 , and CuO, respectively. It was found that even small amounts of transition metal oxides severely change the partial electronic conductivity of ceria while the majority oxygen ion conductivity was only mildly affected: for high oxygen ion conductivity, Fe or Mn oxide addition as well as small amounts of Co oxide are beneficial, as especially the grain boundary conductivity is slightly increased. Addition of V or Cu oxide in contrast increases the minority charge carrier conductivity of electrons and thus enhances the mixed ionic-electronic conductivity. For Co oxide addition, an increasing electronic conductivity with decreasing oxygen partial pressure from 10 −8 to 10 −4 bar at temperatures below 600 • C indicates the changing redox state of Co from divalent at low oxygen partial pressures to trivalent under ambient oxygen partial pressure.

Reactive sintering of dual phase composites for the use as oxygen transport membrane is a promising method enabling lower sintering temperatures as well as low cost raw materials. Ce0.8Gd0.2O2−δ -...