Why is it so difficult to realize Dy4+ in as‐synthesized BaZrO3?

Abstract

AbstractRare‐earth doped barium zirconate (BaZrO3) ceramics are of interest as proton‐conducting and luminescent materials. Here, we report a study of dysprosium (Dy) and other relevant point defects in BaZrO3 using hybrid density‐functional defect calculations. The tetravalent Dy4+ is found to be structurally and electronically stable at the Zr lattice site (i.e., as DyZr0), but most often energetically less favorable than the trivalent Dy3+ (i.e., DyZr–) in as‐synthesized BaZrO3, due to the formation of low‐energy, positively charged oxygen vacancies and the mixed‐site occupancy of Dy in the host lattice. The Dy4+/Dy3+ ratio can, in principle, be increased by preparing the material under highly oxidizing and Ba‐rich conditions and co‐doping with acceptor‐like impurities; however, a post‐synthesis treatment may still be needed to realize a nonnegligible Dy4+ concentration. We also find that certain unoccupied Dy 4f states and the O 2p states in the DyZr0 configuration are strongly hybridized, a feature not often seen in rare‐earth‐containing materials, and that the isolated DyZr defect might be the source of a broad blue emission in band‐to‐defect (“charge‐transfer”) luminescence.