Oxide ion conducting glasses: Synthetic strategies based on liquid state and solid state routes

We describe two different approaches to the formation of glasses in which the oxide ion has high mobility and which therefore may act as solid state anionic conductors. The first is a liquid state approach, utilizing the "barely stable compound" principle. The second avoids the liquid state completely by using the direct transformation of crystal to glass by pressure-induced amorphization. Both methods are applied to obtain glasses high in ZrO₂ content. The glasses obtained have ionic conductivities that are as high as those of pyrochlores, but fall short of those of stabilized zirconia, but may also have a high electronic conductivity depending on state of oxidation. The decoupling index, R_τ, at the glass transition temperature, which measures the freedom of mobile conducting species to move without coupling to their environment, is high, and is comparable to values for the best fluoride ion-conducting glasses. Prospects for broadening the range of oxide ion conducting glasses are considered.