  BaZrO3 exhibits excellent proton conductivity and good high-temperature
stability. It is therefore a promising electrolyte material for solid oxide
fuel cells. The stability of BaZrO3 at high temperatures is generally explained
by the low diffusivity of the O vacancy. Present first-principle
Density-Functional-Theory calculations show that the slow migration of the
doubly positively charged O vacancy at high temperature cannot be solely caused
by the ground-state migration energy but by the contribution of phonon
excitations to the free migration energy. With increasing temperature, the
effective barrier for oxygen vacancy migration increases. At about 1000K, which
is the operating temperature of fuel cells, the calculated O vacancy
diffusivity is more than one order of magnitude lower than that determined
using solely the ground-state migration barrier. The calculated diffusivity
data agree well with experimental results from literature. The present work
reveals that the high-temperature stability of BaZrO3 is mainly due to the
phonon contribution to the free migration energy of the O vacancy.
