Interface Effects on the Ionic Conductivity of Doped Ceria / Yttria-stabilized Zirconia Heterostructures

TL;DR

This study investigates how interface effects in multilayered ceria-zirconia heterostructures influence ionic conductivity, revealing that thinner layers confine charge transport and can lead to insulating behavior in doped ceria layers.

Contribution

It provides new insights into the impact of layer thickness and interfaces on ionic conductivity in doped ceria/zirconia heterostructures, highlighting the role of reduced mobility of oxygen vacancies.

Findings

Conductivity decreases with reducing layer thickness.

Interfacial regions contribute negligibly to total conductivity.

At 2 nm thickness, ceria layers become insulating.

Abstract

Multilayered heterostructures of Ce0.85Sm0.15O2-delta and Y0.16Zr0.92O2-delta of a high crystallographic quality were fabricated on (001) - oriented MgO single crystal substrates. Keeping the total thickness of the heterostructures constant, the number of ceria-zirconia bilayers was increased while reducing the thickness of each layer. At each interface Ce was found primarily in the reduced, 3+ oxidation state in a layer extending about 2 nm from the interface. Concurrently, the conductivity decreased as the thickness of the layers was reduced suggesting a progressive confinement of the charge transport along the YSZ layers. The comparative analysis of the in-plane electrical characterization suggests that the contribution to the total electrical conductivity of these interfacial regions is negligible. For the smallest layer thickness of 2 nm the doped ceria layers are electrically insulating and the ionic transport only occurs through the zirconia layers. This is explained in terms of a reduced mobility of the oxygen vacancies in the highly reduced ceria.