Absence of Morphotropic Phase Boundary Effects in BiFeO3-PbTiO3 Thin Films Grown via a Chemical Multilayer Deposition Method

TL;DR

This study shows that BiFeO3-PbTiO3 thin films prepared via chemical multilayer deposition do not exhibit the expected morphotropic phase boundary effects seen in bulk materials, leading to different structural and functional properties.

Contribution

It demonstrates that multilayer chemical solution deposition alters the phase behavior and properties of BiFeO3-PbTiO3 films compared to bulk predictions, notably eliminating MPB effects.

Findings

Single-phase mixture in all compositions

No enhancement of polarization at MPB

Magnetization increases with BF content

Abstract

Here, we report the unusual behaviour shown by the (BiFeO3)1-x-(PbTiO3)x (BF-xPT) films prepared using a multilayer deposition approach by chemical solution deposition method. Thin film samples of various compositions were prepared by depositing several bilayers of BF and PT precursors by varying the BF or PT layer thicknesses. X-ray diffraction showed that final samples of all compositions show mixing of the two compounds resulting in a single phase mixture, also confirmed by transmission electron microscopy. In contrast to bulk equilibrium compositions, our samples show a monoclinic (MA type) structure suggesting disappearance of morphotropic phase boundary (MPB) about x = 0.30 as observed in the bulk. This is accompanied by the lack of any enhancement of remnant polarization at MPB as shown by the ferroelectric measurements. Magnetic measurements show that the magnetization of the samples increases with increasing BF content. Significant magnetization of the samples indicates melting of spin spirals in the BF-xPT arising from random distribution of iron atoms across the film. Absence of Fe2+ ions in the films was corroborated by X-ray photoelectron spectroscopy measurements. The results illustrate that used thin film processing methodology significantly changes the structural evolution in contrast to predictions from the equilibrium phase diagram as well as modify the functional characteristics of BP-xPT system dramatically.