Sillen-Aurivillius intergrowth phases as templates for naturally layered multiferroics

Abstract

The ferroelectric Sillen-Aurivillius phase Bi5PbTi3O14Cl, a layered structure containing three-layer perovskite-type blocks, has been modified by substituting magnetic transition metal cations M3+ = Cr3+, Mn3+, or Fe3+ for1/3 of the Ti4+ cations, accompanied by co-doping of Bi3+ for Pb2+. The aim of the modification was to produce naturally layered ferroelectromagnetic compounds. Rietveld refinements against high-temperature synchrotron X-ray powder diffraction data show that the resulting new compounds Bi6Ti2MO14Cl undergo non-centrosymmetric (P2an) to centrosymmetric (P4/mmm) ferroelectric phase transitions for Bi6Ti2CrO14Cl at 974.6(2) K, Bi6Ti2MnO14Cl at 913.5(6) K, and Bi6Ti2FeO14Cl at 1044.8(1) K. Ferroelectric properties were measured on Bi6Ti2FeO14Cl using piezoresponse force microscopy which showed typical ferroelectric hysteresis behavior in the polarization with varying field strength as well as a piezoelectric strain. Combined Rietveld refinements against X-ray and neutron powder diffraction data indicate a statistical 1:2 distribution of M3+ and Ti4+ across all three perovskite layers, resulting in highly strained structures (enhancing the ferroelectricity compared to Bi5PbTi3O14Cl) and pronounced spin-glass (cluster glass-type) behavior below Tirr(0) = 4.46 K that we have characterized by detailed magnetic susceptibility and heat capacity measurements.