Correlative chemical and structural nanocharacterization of a pseudo‐binary 0.75Bi(Fe0.97Ti0.03)O3‐0.25BaTiO3 ceramic

Shane J Mccartan,Robert W H Webster,David A Hall,Ilkan Calisir,Ian Maclaren,Gary W Paterson,Thomas A Macgregor

doi:10.1111/jace.17599

Abstract

AbstractFast cooling after sintering or annealing of BiFeO3‐BaTiO3 mixed‐oxide ceramics yields core‐shell structures that give excellent functional properties, but their precise phase assemblage and nanostructure remains an open question. By comparing conventional electron energy loss spectroscopy (EELS) with scanning precession electron diffraction (SPED) mapping using a direct electron detector, we correlate chemical composition with the presence or absence of octahedral tilting and with changes in lattice parameters. This reveals that some grains have a three‐phase assemblage of a BaTiO3‐rich pseudocubic shell; a BiFeO3‐rich outer core with octahedral tilting consistent with an R3c structure; and an inner core richer in Ba and even poorer in Ti, which seems to show a pseudocubic structure of slightly smaller lattice parameter than the shell region. This last structure has not been previously identified in these materials, but the composition and structure fit with previous studies. These inner cores are likely to be non‐polar and play no part in the ferroelectric properties. Nevertheless, the combination of EELS and SPED clearly provides a novel way to examine heterogeneous microstructures with high spatial resolution, thus revealing the presence of phases that may be too subtle to detect with more conventional techniques.

Highlights

Mixed-oxide electroceramics are of great interest due to their unique functional properties and their abundance of technological applications such as piezoelectric sensors, transducers and actuators[1,2,3,4]
By comparing conventional electron energy loss spectroscopy (EELS) with scanning precession electron diffraction (SPED) mapping using a direct electron detector, we correlate chemical composition with the presence or absence of octahedral tilting and with changes in lattice parameters. This reveals that some grains have a three-phase assemblage of a BaTiO3-rich pseudocubic shell; a BiFeO3-rich outer core with octahedral tilting consistent with an R3c structure; and an inner core richer in Ba and even poorer in Ti, which seems to show a pseudocubic structure of slightly smaller lattice parameter than the shell region
To make progress in correlating structure and chemistry, here we study thin sections using a combination of the high spatial resolution techniques of electron diffraction and EELS in the transmission electron microscope/scanning transmission electron microscope (TEM/STEM)

Summary

Introduction

Mixed-oxide electroceramics are of great interest due to their unique functional properties and their abundance of technological applications such as piezoelectric sensors, transducers and actuators[1,2,3,4]. It is well known that tuning material properties, such as stoichiometry, elemental composition or epitaxial strain, can enhance piezoelectric properties[5,6]. These properties are greatly enhanced around the morphotropic phase boundary – a region in the phase diagram in which two structurally competing phases coexist within a narrow range of stoichiometry. Addition of BaTiO3 into the solid solution has been reported to stabilize the BiFeO3 perovskite structure and improve the electrical properties[20,21,22]

Methods

Results

Discussion

Conclusion