title: Incommensurate modulations of relaxor ferroelectric Ca0.24Ba0.76Nb2O6 (CBN24) and Ca0.31Ba0.69Nb2O6 (CBN31).
abstract: CBN crystals show a one- and a two-dimensionally modulated modification. The former is isotypic with orthorhombic Ba4Na2Nb10O30 and the latter with the tetragonal tungsten bronze type of crystal structure. The orthorhombic form irreversibly transforms to the tetragonal polymorph at the ferroelectric phase transition near 603 K. Orthorhombic and tetragonal CBN24 slightly differ in the distribution of the Ba and Ca atoms over the incompletely filled Me1 and Me2 sites. The tetragonal symmetry is further broken in orthorhombic CBN24 by different amplitudes of the positional modulations of O atoms which are symmetrically equivalent in the TTB structure. A similar orthorhombic phase of CBN31 could be obtained by quenching from 1473 K.
authors: Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, Universitätsstraße 150, Bochum D-44801, Germany.
authors: Heribert A
authors: HA
authors: Graetsch
authors: Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, Universitätsstraße 150, Bochum D-44801, Germany.
authors: Chandra Shehkar
authors: CS
authors: Pandey
authors: Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, Universitätsstraße 150, Bochum D-44801, Germany.
authors: Jürgen
authors: J
authors: Schreuer
authors: Institut für Kristallographie, Universität zu Köln, Zülpicher Straße 49b, Köln D-50674, Germany.
authors: Manfred
authors: M
authors: Burianek
authors: Institut für Kristallographie, Universität zu Köln, Zülpicher Straße 49b, Köln D-50674, Germany.
authors: Manfred
authors: M
authors: Mühlberg
keywords: incommensurate modulations; relaxor ferroelectric structures; solid solution series