Electrical properties of ZrO2TiO2Y2O3 system

doi:10.1016/0167-2738(92)90412-I

Solid State Ionics

Volumes 53–56, Part 1, July–August 1992, Pages 436-441

https://doi.org/10.1016/0167-2738(92)90412-I Get rights and content

Abstract

Electrical properties of the mixed conductor, ZrO₂TiO₂y₂O₃ system were measured in the temperature range from 400 to 1400°C. The oxygen partial pressure dependence of the electrical conductivity was measured in the oxygen partial pressure range from 0.21 to 1×10⁻²⁴ atm controlled by H₂CO₂ mixed gas. The total electrical conductivity decreases with increasing titania concentration due to the block of oxygen ions by titanium ions. With no sintering aids like silica and alumina, both bulk and grain boundary conductivity decrease. The electronic conduction is negligibly small and the ionic conduction is dominant in high oxygen partial pressure range. The electronic conductivity appears at low oxygen partial pressure: lower than 10⁻¹⁷ atm and at 1000°C in YSZ containing 10 mol% titania. The electronic conduction of this system is n-type and is due to small polaron hopping mechanism caused by electrons hopping between Ti³⁺ and Ti⁴⁺ ions.

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Mixed oxide-ionic and electronic conductors are required for various electrochemical applications, including electrode materials for solid oxide fuel cells and permeating membranes for syngas production. Strategies to enhance mixed conduction, either doping electrolytes with mixed-valence cations [1–4] or processing composites with an electrolyte and an electronic conductor [5–11], proved to be of limited effectiveness. The levels of electronic conductivity obtained by compositional excursions are usually modest, and undesirable reaction or development of ion-blocking interfaces is common in the case of composites.
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Taking advantage of the fact that TiO₂ additions to 8YSZ cause not only the formation of a titania-doped YSZ solid solution but also a titania-doped YTZP solid solution, composite materials based on both solutions were prepared by solid state reaction. In particular, additions of 15 mol% of TiO₂ give rise to composite materials constituted by 0.51 mol fraction titania-doped yttria tetragonal zirconia polycrystalline and 0.49 mol fraction titania-doped yttria stabilized zirconia (0.51TiYTZP/0.49TiYSZ). Furthermore, Y₂(Ti_1−yZr_y)₂O₇ pyrochlore is present as an impurity phase with y close to 1, according to FT-Raman results. Lower and higher additions of titania than that of 15 mol%, i.e., x=0, 5, 10, 20, 25 and 30 mol% were considered to study the evolution of 8YSZ phase as a function of the TiO₂ content. Furthermore, zirconium titanate phase (ZrTiO₄) is detected when the titania content is equal or higher than 20 mol% and this phase admits Y₂O₃ in solid solution according to FE-SEM-EDX.
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Electrical properties of ZrO2TiO2Y2O3 system

Abstract

Int. J. Hydrogen Energy

Solid State Ionics

Solid State Ionics

Solid State Ionics

J. Phys. Chem. Solids

Denki Kagaku

J. Am. Ceram. Soc.

Electrical properties of ZrO₂TiO₂Y₂O₃ system