Hydration entropy of BaZrO3 from first principles phonon calculations

摘要: The impact of phonons on the hydration and defect thermodynamics undoped acceptor (Sc, In, Y Gd) doped BaZrO3 is addressed by means first principles supercell calculations. In contrast to previous, similar investigations, we evaluate contributions from all phonon modes, also pressure/volume effects properties. calculations are performed at GGA-level with PBE RPBE functionals, both which predict for a stable cubic perovskite structure. For dopants, vibrational formation entropy doubly positively charged oxygen vacancy significantly lower than that protonic , therefore dominant contribution hydration, in addition loss H2O(g). large, negative stems large local structural relaxations, contraction entire corresponding blue-shift spectrum. Neglect free energy leads considerable error (100 kJ mol−1 1000 K). systems, calculated becomes more order < Gd Sc, volume become increasing dopant ion size. Both functionals give entropies undoped, Sc- In-doped BaZrO3. However, larger Y- Gd-ions, underestimates (too negative) due poor representation low frequency modes R point Brillouin zone. good agreement experimental results, lending support applicability adopted method.