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High resolution neutron and X‐ray diffraction studies as a function of temperature and electric field of the ferroelectric phase transition of RDP
Author(s) -
Mattauch S.,
Heger G.,
Michel K. H.
Publication year - 2004
Publication title -
crystal research and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.377
H-Index - 64
eISSN - 1521-4079
pISSN - 0232-1300
DOI - 10.1002/crat.200410289
Subject(s) - ferroelectricity , tetragonal crystal system , orthorhombic crystal system , phase transition , crystallography , neutron diffraction , condensed matter physics , materials science , dielectric , phase (matter) , crystal structure , chemistry , physics , optoelectronics , organic chemistry
Neutron and high resolution X‐ray diffraction investigations on perfect single crystals of RbH 2 PO 4 (RDP), a hydrogen bonded ferroelectric of KDP type are reported. The results of crystal structure analysis from diffraction data, below and above the paraelectric ‐ ferroelectric phase transition, support a disorder ‐ order character of [PO 4 H 2 ] ‐ ‐groups. The tetragonal symmetry of the paraelectric phase with the double well potential of the hydrogen atoms obtained by diffraction, results simply from a time‐space average of orthorhombic symmetry. According to the group ‐ subgroup relation between the tetragonal space group I42d and the orthorhombic Fdd 2 a short range order of ferroelectric clusters in the tetragonal phase is observed. With decreasing temperature the ferroelectric clusters increase and the long range interaction between their local polarisation vectors leads to the formation of lamellar ferroelectric domains with alternating polarisation directions at T C = 147 K. From the high resolution X‐ray data it is concluded that below T C the ferroelastic strain in the (a,b)‐plane leads to micro‐angle grain boundaries at the domain walls. The tilt angle is enhanced by an applied electric field parallel to the ferroelectric axis. The resulting dislocations at the domain walls persist in the paraelectric phase leading to a memory effect for the arrangement of twin lamellae. With increased electric field the phase transition temperature T C is decreased. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)