Structure and decomposition of ceramic Ba3Y4O9
Abstract We report the results of X-ray and neutron scattering examination of the compound Ba 3 Y 4 O 9 , which has been reported as an ionic conductor above 370°C. We have identified that the compound is isostructural with Ba 3 Yb 2 Y 2 O 9 and that there are no partially filled oxygen sites which might support a high ionic conductivity nor any sign of a phase transition at temperatures up to 700°C. It is also shown that the observed enhanced ionic conductivity upon exposure to moist air is associated with decomposition of the Ba 3 Y 4 O 9 phase. We have further demonstrated, using electron diffraction and Raman spectroscopy, that during the early stages of the decomposition there is a growth of amorphous barium hydroxides which are likely to be the source of the observed ionic conductivity.