Perovskites in low dimensional multi-layer structure types

Abstract

This study introduces examples of structure property relationships within the multi-layered Sillen-Aurivillius family (shown in Figure) and aims to investigate the effect of chemical doping and lattice matching effects. The first example involves doping 1/3 of the n = 3 ferroelectric perovskite layers with magnetic transition metal cations in Bi5PbTi3O14Cl [1] with charge balancing by removing Pb2+for Bi3+. A statistical 1:2 distribution of M3+and Ti4+across all three perovskite layers was found in Bi6Ti2MO14Cl, M = Cr3+, Mn3+, Fe3+, resulting in highly strained structures (enhancing the ferroelectricity compared to Bi5PbTi3O14Cl) and pronounced spin-glass behavior below Tirr(0) = 4.46 K. Ferroelectric transitions were observed at high temperature for each of the new compounds. Ferroelectric properties were also measured on Bi6Ti2FeO14Cl using piezoresponse force microscopy showing hysteretic phase behavior. A new n = 2 Sillen-Aurivillius compound Bi3Sr2Nb2O11Br, based on Bi3Pb2Nb2O11Cl [2], was synthesized by simultaneously replacing Pb2+with Sr2+and Cl-with Br-. Inter-layer mismatch prevented the formation of Bi3Sr2Nb2O11Cl and Bi3Pb2Nb2O11Br. Sr2+doping reduces the impact of the stereochemically active 6s2lone pair found on Pb2+and Bi3+, resulting in a stacking contraction in the lattice parameters by 1.22 % and an expansion of the a-b plane by 0.25 %, improving inter-layer compatibility with Br-. X-ray Absorption Near Edge Structure spectra analysis shows that the ferroelectric distortion of the B-site cation is less apparent in Bi3Sr2Nb2O11Br compared to Bi3Pb2Nb2O11Cl. Variable-temperature neutron diffraction data show no evidence for a ferroelectric distortion.