Structural and electrical behaviour in Bi14YO22.5
Abstract
Structure and electrical conductivity in the oxide ion conducting compound Bi14YO22.5 have been investigated by powder X-ray and neutron diffraction, a.c. impedance spectroscopy, measurements of transference number and ab initio molecular dynamics (MD) simulations. Phase behaviour was studied using variable temperature X-ray diffraction and differential thermal analysis. The structure at room temperature is of the βIII tetragonal-type, details of which are discussed, including its relationship to both β and δ phases of Bi2O3. Bi14YO22.5 undergoes a reversible phase transition to a cubic δ-Bi2O3 type phase at high temperatures. This phase exhibits very high electrical conductivity, with transference numbers indicating that this conductivity is almost purely ionic in nature. MD simulations confirm 3-dimensional oxide ion transport in the βIII-phase.