The crystal structure and physical properties of Bi3Pb2Nb2O11Cl, a member of the Sillen−Aurivillius phase intergrowth family, have been probed using powder neutron diffraction,
high-resolution transmission electron microscopy (HRTEM), second harmonic generation
(SHG) tests, and alternating current impedance methods. It is shown that this compound
undergoes a diffuse ferroelectric type phase transition at T
c ∼ 683 K. Although the powder
neutron diffraction data show that the crystal structure has pseudo-tetragonal symmetry
(parent space group P4/mmm, a
p = 3.910 38(6) and c
p = 18.8342(3) Å at 298 K), electron
diffraction data clearly show a weak superlattice (a
o ∼ b
o ∼ (2)1/2
a
p, c
o = c
p) compatible with
a reduction of symmetry to orthorhombic, analogous to that observed in the related Aurivillius
phases, such as SrBi2Ta2O9. Detailed analysis of the SHG data as a function of temperature
suggests the existence of ordered polar nanodomains, compatible with the observation of
“average” tetragonal symmetry in the neutron diffraction data. These observations, together
with the presence of marked frequency dependence of T
c, point toward a relaxor type
ferroelectric behavior. The nature of the crystal structure, namely, a regular intergrowth of
Aurivillius-like and Sillen-like blocks, [M2O2]/[MNb2O7]/[M2O2]/[Cl] [M = Bi, Pb], has been
established from both Rietveld refinement of the powder neutron data and directly from
HRTEM images. The observation of ferroelectricity in this material suggests the existence
of a wider family of new ferroelectrics analogous to the Aurivillius phases.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.