Structure–property correlations in the new ferroelectric Bi5PbTi3O14Cl and related layered oxyhalide intergrowth phases

Abstract

The crystal structure and electrophysical properties of the layered intergrowth phase Bi₅PbTi₃O₁₄Cl have been studied using powder neutron diffraction, ac impedance and second harmonic generation methods. This phase adopts a structure based on a regular intergrowth of Aurivillius-like and Sillén-like blocks in the layer sequence ⋯[M₂O₂][M₂Ti₃O₁₀][M₂O₂][Cl]⋯, and is therefore closely structurally related to the well-known ferroelectric Bi₄Ti₃O₁₂. The phase adopts the polar orthorhombic space group P2an at temperatures below 590 °C, and transforms directly to a centrosymmetric tetragonal phase, space group P4/mmm, at that temperature. This abrupt structural phase transition is consistent with a sudden loss of SHG signal and a dielectric maximum at the same temperature. The structural features and electrophysical behaviour of this phase in relation to Bi₄Ti₃O₁₂ and related layered oxides/oxyhalides are discussed.