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Antiferroelastic structural transitions in PrAlO 3 by means of neutron diffraction
Author(s) -
Watanabe S.,
Hidaka M.,
Yoshizawa H.,
Wanklyn B. M.
Publication year - 2006
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.200541211
Subject(s) - octahedron , crystallography , neutron diffraction , phase transition , phase (matter) , ion , perovskite (structure) , bar (unit) , chemistry , diffraction , crystal structure , materials science , physics , condensed matter physics , optics , organic chemistry , meteorology
Structural phase transitions of the perovskite‐type PrAlO 3 have been studied by using neutron diffraction. The results show that, on cooling, the structures are successively transformed from R $ \bar 3 $ c (Phase II) to Imma (Phase III), Imma (Phase IV), I4/mcm (Phase V) by the 215‐K, 153‐K, and 122‐K transitions. The tilting schemes in Phase III, IV and V are mainly characterized by ( ψ a = ψ c , ψ b = 0), ( ψ a ≠ ψ c , ψ b = 0), and ( ψ c , ψ a = ψ b = 0), respectively, where ψ a , ψ b and ψ c are rotational angles around a ‐, b ‐, and c ‐primitive axes of the AlO 6 octahedron. The refreezes of the condensed R 25 yand R 25 xoptical soft modes occurring at about 215 K and 122 K are interpreted by correlation with the cooperative Jahn–Teller distortion (JTD) of the Pr 3+ –4f orbitals in the PrO 12 polyhedra. The phase IV is characterized as an intermediate state, in which the ψ a tilts are continuously reduced by the JTD and disappear just above the 122‐K transition. The easy mobility of the domain walls suggests the PrAlO 3 crystal to be of antiferroelastic nature, an unusual property that results from the cooperative displacements of O ions induced by the correlation between the antiphase tilts along primitive axes of the AlO 6 octahedra and the JTD around Pr +3 ions in PrO 12 polyhedra. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)