Decomposition of -alumina in an oxygen potential gradient

Single phase sodium/3-alumina solid electrolyte was found to undergo isothermal phase separation in electrochemical ceils, where a large oxygen potential gradient was imposed across the electrolyte and electrodes, not reversible to sodium ions, were short circuited. The experimental conditions and evidence of decomposition are outlined and a thermodynamic explanation for the phenomenon is given. This finding may lead to new methods for making multi-layered ceramic materials involving ionic conductors.