Abstract
High-temperature phase behavior in the system has been studied by using high-resolution neutron powder diffraction. Each of the three compositions studied in the Na-rich part of the phase diagram (viz., , and 0.12) shows evidence for distinct and complex structural modulations based on different tilting schemes of octahedral units. Whilst octahedral tilting is prevalent in the structural chemistry of perovskites the details of the long-range tilt phases are distinct from those previously observed in itself. A phase with a well-defined fourfold superlattice is observed for the composition , and yet more complex phases with modulations based on 20-fold and 30-fold repeats are observed for and , respectively. This peculiar structural frustration makes the system a most structurally complex “simple” perovskite.
2 More- Received 21 February 2018
DOI:https://doi.org/10.1103/PhysRevB.97.224105
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