Takao Ishii

Structural phase transition and ionic conductivity in 0.88ZrO2(0.12 − x)Sc2O3xAl2O3

Abstract The structural phase transition and ionic conductivity of 0.88ZrO2(0.12 − x)Sc2O3xAl2O3 (0 ≤ x ≤ 0.005) was examined to clarify the mechanism of the cubic phase stabilization in this system. The temperature of the transition from rhombohedral to cubic decreases monotonously from 660 °C (x = 0) to 500 °C (x = 0.004) and no transition is observed at x = 0.005. The stabilization mechanism may be closely related to the strain induced in the crystalline lattice caused by adding the second dopant Al2O3. This is supported by the experimental result which reveals that the compositional dependence of the transition temperature in the 0.88ZrO2(0.12 − x)Sc2O3xM2O3 system strongly depends on the ionic radius of second dopant.

Temperature dependence of ionic conductivity in (1 − x)ZrO2−(x − y)Sc2O3−yYb2O3 electrolyte material

The temperature dependence of the ionic conductivity of (1 − x)ZrO2−(x − y)Sc2O3−yYb2O3 (x = 0.07–0.15, y = 0.00–0.03) was examined to clarify the origins of the ionic conductivity decrease at low temperature. For y = 0.02–0.03 in this system, the cubic phase was stabilized at room temperature and discontinuity in the ionic conductivity disappears. The Arrhenius plots of the ionic conductivity for the stabilized samples were curved. The grain boundary resistance for (1 − x)ZrO2−(x − 0.03)Sc2O3−0.03Yb2O3 (x = 0.07–0.15) was separated from the total resistance with the AC impedance method. This allowed us to conclude that grain boundary resistance is not the cause of the curvature in the Arrhenius plots for this system.

Structural phase transition and ion conductivity in 0.88ZrO2−0.12Sc2O3

It is found that oxygen ion conductor 0.88ZrO2−0.12Sc2O3 shows a discontinuous change in ion conductivity and a structural phase transition at around 650°C. The temperature dependence of ion conductivity shows a clear hysteresis at transition temperature. The crystal structure changes reversibly from rhombohedral to cubic at the transition temperature. The compound 0.88ZrO2− 0.12Sc2O3 exhibits a first-order phase transition to a fast oxygen-ion conductor. The high temperature phase with fast ion conductivity is stabilized in the low temperature region by the addition of a dopant such as Gd2O3.

Ionic conductivity and morphology in Sc2O3 and Al2O3 doped ZrO2 films prepared by the sol–gel method

Abstract We used the sol–gel method to deposit zirconia films doped with Sc2O3 and Al2O3 on alumina substrates. We investigated the annealing temperature dependence of the ionic conductivity and morphology in the films whose composition was 0.85ZrO2–0.11Sc2O3–0.04Al2O3. The film thickness was controlled from about 0.1 to 1.0 microns by controlling the coating time. The films prepared by this method are stabilized in the cubic phase. Annealing at 1200°C produces isotropic and well-sintered films. The ionic conductivity of the annealed film was 7.6×10−2 S/cm at 800°C, which is comparable to that of bulk samples prepared by solid reaction at 1620°C.

Low temperature operation of solid oxide fuel cell with a ZrO[sub 2]-Sc[sub 2]O[sub 3]-Al[sub 2]O[sub 3] system electrolyte

This paper describes the low temperature operation of a solid oxide fuel cell using cubic stabilized zirconia in the ZrO[sub 2]-Sc[sub 2]O[sub 3]-Al[sub 2]O[sub 3] system as an electrolyte. The hydrogen-oxygen fuel cell was fabricated by using La[sub 0.8]Sr[sub 0.2]MnO[sub 3] as the cathode material and Ni-YSZ as the anode material. The maximum power density is 0.63 W/cm[sup 2] at 800 C and 1.0 W/cm[sup 2] at 880 C. The current-voltage performance of this fuel cell suggests that the present electrolyte is a good candidate for fuel cells operating in the temperature range between 800 and 900 C.