Ionic Conductivity of Mesostructured Yttria-Stabilized Zirconia Thin Films with Cubic Pore Symmetry—On the Influence of Water on the Surface Oxygen Ion Transport

Abstract

Thermally stable, ordered mesoporous thin films of 8 mol % yttria-stabilized zirconia (YSZ) were prepared by solution-phase coassembly of chloride salt precursors with an amphiphilic diblock copolymer using an evaporation-induced self-assembly process. The resulting material is of high quality and exhibits a well-defined three-dimensional network of pores averaging 24 nm in diameter after annealing at 600 °C for several hours. The wall structure is polycrystalline, with grains in the size range of 7 to 10 nm. Using impedance spectroscopy, the total electrical conductivity was measured between 200 and 500 °C under ambient atmosphere as well as in dry atmosphere for oxygen partial pressures ranging from 1 to 10(-4) bar. Similar to bulk YSZ, a constant ionic conductivity is observed over the whole oxygen partial pressure range investigated. In dry atmosphere, the sol-gel derived films have a much higher conductivity, with different activation energies for low and high temperatures. Overall, the results indicate a strong influence of the surface on the transport properties in cubic fluorite-type YSZ with high surface-to-volume ratio. A qualitative defect model which includes surface effects (annihilation of oxygen vacancies as a result of water adsorption) is proposed to explain the behavior and sensitivity of the conductivity to variations in the surrounding atmosphere.

Thermal stability, electrochemical and structural characterization of hydrothermally synthesised cobalt ferrite (CoFe2O4)

“…Thus, the total resistance of the sample is obtained at the intercept point of the rst semicircle on the x-axis. The merging of the semicircles at high frequencies representing the grain and the grain boundary contribution imply that the crystallites are in the nanosize range 46,49,54 in agreement with the SEM and XRD observation.…”

“…a third semi-circle, is observed which is caused by the electric charge transfer at the Pt electrode as oen observed for oxide materials. 48,49 However, this third semi-circle is not considered in the tting to ensure continuity between the different temperature regimes by using the same equivalent circle. The corresponding ts to the data are shown in Fig.…”

“…3 as solid lines. From the constant phase elements Q i the capacitance of the corresponding transport process can be calculated: [49][50][51]…”

“…with decreasing grain size the capacity shis to lower values resulting in an overlap of the bulk and grain boundary semicircle in nanocrystalline samples. 46,49,52 Not only the grain size, but also the temperature can result in a merging of the two semicircles due to the temperature dependence of the resistance as shown in Fig. 3(b).…”

Linking the Electrical Conductivity and Non-Stoichiometry of Thin Film Ce1−xZrxO2−δ by a Resonant Nanobalance Approach

“…Hence, accounting for the morphology of thin films studied herein, the influence of porosity and roughness (increasing with Zr fraction) should not be excluded. The effective charge of subsurface atoms in thin films with large surface area-to-volume ratios may be different from that in bulk materials [54][55][56]95], e.g., the surface oxygen vacancies may have fractional charges, which leads to conductivities with slopes between −1/3 and −1/2 at reducing conditions. Such steeper slopes are actually observed for Zr-rich CZO-33, CZO-50 and CZO-67 samples at 600 • C upon transition from conductivity plateau at pO 2 = 10 −14 bar (Figure 8c-e).…”