Ionomigration of Neutral Phases in Ionic Conductors

Without sensing any physical force, a neutral object in an ion conducting solid can move in a uniform electrochemical fi eld by coupling a global ion wind with localized counterion diffusion at the interface. This happens to pores and gas bubbles at 840 ° C in a fast O 2– conductor, yttria-stabilized zirconia (YSZ), despite having cations that are essentially frozen with lattice diffusivities 10 12 times slower than the O 2 − diffusivity. Through-thickness migration and massive electro-sintering in thin YSZ ceramics are observed at voltages similar to those in YSZ fuel cells and electrolysis cells. This effect should apply to any electrochemically-loaded multiphase ionic conducting solid, with or without an electric fi eld, and can lead to electrolyte sintering, phase accumulation and electrode debonding, resulting in unexpected benefi t or damage in electrochemical devices. As the velocity obeys a pseudo StokesEinstein equation, inversely proportional to the object size, an especially enhanced size effect is expected in nanocomposites.