An in-situ neutron diffraction study of the crystal structure of PrBaCo2O5+δ at high temperature and controlled oxygen partial pressure

Neutron powder diffraction was used to characterize the layered perovskite PrBaCo 2 O 5 + δ (PBCO) under in-situ conditions from 573 to 852 °C and at p O 2 = 10 − 1 –10 − 4 atm. The data were fit to a tetragonal model in space group P4/mmm . The oxygen vacancies were found to be localized within the Pr layer, with total oxygen stoichiometry between 5.57(1) and 5.17(2). This was verified by coulometric titration. The location of these vacancies and the anisotropic displacement of the surrounding oxygen anion sites indicate that ion transport occurs via a hopping mechanism between O sites in the Pr layer and the nearest neighbor sites in the Co layer. While the direct hopping distance between these sites was found to be greater for PBCO than previously reported for NdBaCo 2 O 5 + δ , the larger radius of Pr 3 + stabilizes a higher concentration of mobile anions within the Ln layer.