Investigation about the electrochemical reduction in 3YSZ, related phase transition and consequences

TL;DR

This study investigates how electrochemical reduction of 3YSZ varies with oxygen partial pressure and atmosphere, revealing a phase transition from tetragonal to FCC rocksalt ZrO or ZrON, affecting electrical and structural properties.

Contribution

It provides new insights into the phase transition mechanisms of 3YSZ under electrochemical reduction at high temperature and electric field.

Findings

Identification of two distinct states during reduction

Observation of rapid phase transition to FCC rocksalt ZrO or ZrON

Correlation between phase change and electrical conductivity increase

Abstract

In this research the electrochemical reduction of 3YSZ was investigated in various atmospheres with different oxygen partial pressures under an electric field of 25 V/cm at an environmental temperature of 800 {\deg}C. At a certain oxygen partial pressure insufficient incorporation of oxygen in the sample led to electrochemical reduction of YSZ which shows two clearly distinguishable states. First, greying of the material without a significant change in properties was detected which then transitioned into a second stage where a fundamental phase transition in the material happened within seconds from tetragonal 3YSZ towards FCC rocksalt ZrO or ZrON, dependent on the atmosphere. This phase transition is accompanied by blackening of the material, sudden increase in electrical conductivity, current concentration, and an obvious change in Raman spectrum.