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Title: The crystal structures of Pb2ScTaO6 and Pb2ScNbO6 in the paraelectric and ferroelectric states
Authors: Baba-Kishi, K
Woodward, P
Knight, K
Keywords: Neutron diffraction
Relaxor ferroelectric oxides
Issue Date: 2001
Publisher: Taylor & Francis Inc.
Source: Ferroelectrics, 2001, v. 261, no. 1-4, p. 685-690 How to cite?
Journal: Ferroelectrics 
Abstract: Two systems were studied on high-resolution neutron time-of-flight powder diffraction (HRDP), a totally B-site disordered ceramic disk of Pb2ScNbO6, and a partially ordered ceramic block of Pb2ScTaO6. We found Pb2ScNbO6 to be fully disordered, space group Pm3m with lattice constant 4.08153(1)Angstrom, whereas Pb2ScTaO6 was found to be 86(1)% ordered with space group Fm3m and lattice constant 8.14866(1)Angstrom. The high-resolution on HRDP allowed the crystal system in both compounds to be identified as rhombohedral. Two space groups, R3 and R3m were tested. A large asymmetry was found in the 3.0Angstrom co-ordination sphere of Pb, which changes its coordination number from 12 to 9 on the ferroelectric transition. The co-ordination of oxygen around the Pb suggests that the phase transition is related to the de-localisation of a stereochemically active lone pair. In both Pb2ScTaO6 and Pb2ScNbO6, the major displacements occurred for the Pb(s) in the order of 0.25Angstrom, whilst the displacements in the B-site octahedra were much smaller.
Description: 3rd Asian Meeting on Ferroelectricity (AMF-3), Hong Kong, Peoples R China, 12-15 December 2000
ISSN: 0015-0193
EISSN: 1563-5112
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