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A new family of ferroelectric tetragonal tungsten bronze phases, Ba2MTi2X3O15

Authors
Journal
Journal of the European Ceramic Society
0955-2219
Publisher
Elsevier
Publication Date
Volume
25
Issue
12
Identifiers
DOI: 10.1016/j.jeurceramsoc.2005.03.198
Keywords
  • Powders-Solid State Reaction
  • Dielectric Properties
  • Ferroelectric Properties
  • Electron Microscopy
  • Neutron Diffraction

Abstract

Abstract The compositions Ba 2MTi 2X 3O 15: M = La, Pr, Nd, Sm, Eu, Gd, Dy, Bi; X = Nb, Ta form a new family of ferroelectric phases. With larger M cations, La, Bi, the materials exhibit relaxor behaviour with sub-ambient Tc. With decreasing M size, a sharp first order ferroelectric phase transition is observed and Tc rises to a maximum at ∼330 °C for Gd. The phases are tetragonal tungsten bronzes with A-site order (BaM) and non-statistical B-site disorder (of Ti, Nb for M = La). All phases show a weak superstructure with doubled c and multiple periodicity parallel to [1 1 0] that is incommensurate for the relaxor ferroelectrics (M = La, Bi) but commensurate for the remainder. The phases exhibit complex non-stoichiometry with variable Ba:M and Ti:X ratios as well as variable oxygen content.

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