Structure and thermodynamic stability of hydrogen interstitials in BaZrO₃ perovskite oxide from density functional calculations

Density functional calculations have been used to study the electronic structure, preferred sites in the lattice, formation energies and vibrational frequencies for hydrogen interstitials in different charge states in the cubic phase of perovskite-structured BaZrO₃. By combining ab initio results with thermodynamic modeling, defect formation at finite temperature and pressure has been investigated. We demonstrate how the site selectivity and spatial distribution of dopant atoms in the lattice can be affected by changes in the environmental conditions (atomic chemical potentials, oxygen partial pressure and temperature) used during processing of the material. In addition, we have calculated the thermodynamic parameters of the water uptake reaction for an acceptor-doped BaZrO₃ crystal in equilibrium with a humid atmosphere. The interaction energies between a protonic defect and the investigated Ga, Gd, In, Nd, Sc, and Y dopants were found to be attractive, and we show that a simple model of defect association may reproduce an experimentally observed trend in the hydration enthalpy.