Quenching-assisted actuation mechanisms in core–shell structured BiFeO₃–BaTiO₃ piezoceramics

Abstract

Electromechanical actuation in piezoceramics is usually enhanced by creating chemically homogeneous materials with structurally heterogeneous morphotropic phase boundaries, leading to abrupt changes in ion displacement directions within the perovskite unit cell. In the present study, an alternative mechanism to enhance electromechanical coupling is found in both chemically and structurally heterogeneous BiFeO 3 -BaTiO 3 lead-free piezoceramics. Such a mechanism is observed in a composition exhibiting core-shell type microstructure, associated with donor-type substitution of Ti 4+ for Fe 3+ , and is primarily activated by thermal quenching treatment. Here, we describe the use of in situ highenergy synchrotron X-ray powder diffraction upon the application of a high electric field to directly monitor the ferroelectric and elastic interactions between these composite-like components, formed as core and shell regions within grains. Translational short or long-range ordering is observed in the BiFeO 3 -depleted shell regions which undergo significant structural alterations from pseudocubic Pm % 3mrelaxor-ferroelectric in slow-cooled ceramics to rhombohedral R3c or R3m with long-range ferroelectric order in the quenched state. The strain contributions from each component are calculated, leading to the conclusion that the total macroscopic strain arises predominantly from the transformed shell after quenching. Such observations are also complemented by investigations of microstructure and electrical properties, including ferroelectric behaviour and temperature-dependent dielectric properties.

Fatigue resistant lead-free multilayer ceramic capacitors with ultrahigh energy density

“…Immiscibility in part can be suppressed by quenching and by careful selection of dopants. 70,71,[74][75][76] The core-shell structure in BF-BT-0.13BLN ceramics was investigated further by transmission electron microscopy (TEM) (Fig. S8, ESI †) and exhibits small tweed domains (core) and a shell of nanodomains, similar to previous reports in BF-BTbased ceramics.…”

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

“…This either suggests that the structure is an untilted pseudocubic perovskite, as has been suggested in previous reports on the more BaTiO 3 -rich phases in this system (23,47), or a rhombohedral phase with very small tilting such that the intensity in the superlattice spots is undetectably small (26). Unsurprisingly, these areas are generally those with the largest lattice parameter, as was already expected from previous publications on this system (23,26).…”

“…It is clear from the data presented that the core‐shell structure in the quenched samples is a three‐phase one, not the two‐phase structure previously posited 25,26 . The three phases will be discussed in turn in the forthcoming paragraphs.…”

“…Samples were synthesised by the solid state reaction method based on the chemical formula of 0.75(3% Ti-doped BiFeO 3 )−0.25BaTiO 3 . More details are given by Calisir et al (26).…”

“…Using precession electron diffraction, this area consistently did not show ½{ooo} reflections, which are a sign of antiphase tilting (23,26,34) -even careful examination of the raw data focusing on those positions found no evidence for these. This either suggests that the structure is an untilted pseudocubic perovskite, as has been suggested in previous reports on the more BaTiO 3 -rich phases in this system (23,47), or a rhombohedral phase with very small tilting such that the intensity in the superlattice spots is undetectably small (26). Unsurprisingly, these areas are generally those with the largest lattice parameter, as was already expected from previous publications on this system (23,26).…”