Location and lattice dynamics of a proton in the perovskite structure

Abstract

A domain of locations of a proton in the perovskite structure is determined by studying the local structure and a hard sphere point charge model. Two intra- and one inter-octahedron processes with different energy barriers of ⟨E1⟩, ⟨E2⟩, and ⟨E3⟩ have been studied, respectively. The order of the energy barriers is predicted as ⟨E3⟩ > ⟨E1⟩ ≥ ⟨E2⟩ by studying both the changes of bonding in these processes and the charge imbalance between the acceptor dopant ion and the B type ion. The inter-octahedron hopping, ⟨E3⟩, is shown to be a necessary and rate limiting step by using percolation and charge imbalance argument. This result differs with earlier calculations, however, it agrees with the result of quasi-elastic neutron and other experimental results. Through studying the lattice dynamics of a 1D O–H chain and its monomer, we have developed new formulae for a hydrogen bond system and applied them to explain the experimentally observed red-shift and broadening of the O–H vibration peak. These phenomena are revealed as indications of the quasi-free state of a proton instead of the formation of hydrogen bond.