Structural phase transitions in the relaxor ferroelectric Pb{sub 2}Bi{sub 4}Ti{sub 5}O{sub 18}

• Published in: Journal of solid state chemistry Vol. 182; no. 10
• Main Authors: Goff, Richard J., Lightfoot, Philip
• Format: Journal Article
• Language: English
• Published: United States 15-10-2009
• Subjects: BISMUTH COMPOUNDS; CHALCOGENIDES; COHERENT SCATTERING; CRYSTAL LATTICES; CRYSTAL STRUCTURE; CRYSTALLOGRAPHY; CURIE POINT; DIELECTRIC MATERIALS; DIFFRACTION; ELECTRICAL PROPERTIES; ELECTRON DIFFRACTION; FERROELECTRIC MATERIALS; LEAD COMPOUNDS; MATERIALS; MATERIALS SCIENCE; NEUTRON DIFFRACTION; OXIDES; OXYGEN COMPOUNDS; PHASE TRANSFORMATIONS; PHYSICAL PROPERTIES; POLARIZATION; POWDERS; SCATTERING; SPACE GROUPS; SYMMETRY GROUPS; TETRAGONAL LATTICES; THERMODYNAMIC PROPERTIES; TITANIUM COMPOUNDS; TRANSITION ELEMENT COMPOUNDS; TRANSITION TEMPERATURE
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2009.06.038

The relaxor ferroelectric Pb{sub 2}Bi{sub 4}Ti{sub 5}O{sub 18} has been studied by Rietveld refinement of powder neutron diffraction data collected at temperatures of 100, 250 and 400 deg. C. Our refinements are compatible with the 'average' crystal structure of Pb{sub 2}Bi{sub 4}Ti{sub 5}O{sub 18} undergoing the phase transition sequence F2mm->I4mm->I4/mmm as a function of increasing temperature, with the latter phase being observed above the known ferroelectric Curie temperature, T{sub m}, and the intermediate phase consistent with a previously observed dielectric anomaly around 207 deg. C. The results are, however, in conflict with both observation of a symmetry lowering (to space group B2eb) in the lowest temperature phase, observed by electron diffraction, and also with electrical property measurements, which suggest both a- and c-axis polarisation up to T{sub m}. Nevertheless, these crystallographic results are consistent with the observation of relaxor behaviour in this material, and underline the importance of considering 'long-range' versus 'local' structural effects in relaxor materials. - Abstract: A powder neutron diffraction study suggests that the relaxor ferroelectric Pb{sub 2}Bi{sub 4}Ti{sub 5}O{sub 18} undergoes the phase transition sequence F2mm-I4mm-I4/mmm with increasing temperature. Display Omitted