Dual strain mechanisms in a lead-free morphotropic phase boundary ferroelectric

Abstract

Electromechanical properties such as d33 and strain are significantly enhanced at morphotropic phase boundaries (MPBs) between two or more different crystal structures. Many actuators, sensors and MEMS devices are therefore systems with MPBs, usually between polar phases in lead (Pb)-based ferroelectric ceramics. In the search for Pb-free alternatives, systems with MPBs between polar and non-polar phases have recently been theorized as having great promise. While such an MPB was identified in rare-earth (RE) modified bismuth ferrite (BFO) thin films, synthesis challenges have prevented its realization in ceramics. Overcoming these, we demonstrate a comparable electromechanical response to Pb-based materials at the polar-to-non-polar MPB in Sm modified BFO. This arises from ‘dual’ strain mechanisms: ferroelectric/ferroelastic switching and a previously unreported electric-field induced transition of an anti-polar intermediate phase. We show that intermediate phases play an important role in the macroscopic strain response, and may have potential to enhance electromechanical properties at polar-to-non-polar MPBs.

Temperature dependent piezoelectric response and strain–electric-field hysteresis of rare-earth modified bismuth ferrite ceramics

“…These regions with visible domains were previously identified as the R3c phase, and the regions exhibiting no PFM contrast (i.e. no visible domains) were identified as the Pbam phase 33,41 . While PFM with its detection limitation (>40 nm) was unable to identify a domain structure in the Pbam phase, previous reports demonstrate that nanosized regions with greyscale contrast are visible with TEM, but are unidentified 33 .…”

“…Depoling temperatures were measured ex-situ, meaning that the samples were annealed to the desired temperature and then cooled to room temperature before measuring the d 33 . The d 33 was determined at room temperature with a Take Control® piezometer system PM10 at ~200 Hz of driving stress frequency.…”

“…The d 33 was determined at room temperature with a Take Control® piezometer system PM10 at ~200 Hz of driving stress frequency. The onset temperature of depoling was defined as the temperature at which the d 33 first drops below its initial room temperature value.…”

“…Peak-to-peak strains (S pp ) for asymmetric loops were determined as an absolute maximum value obtained by taking the difference between maximum and minimum values in strain-time plots. 33 analysis samples were poled with a DC electricfield using a Spellman SL150 amplifier. Samples were submerged in a silicone-oil bath and kept at room temperature while the DC field was applied for 15 min at the maximum magnitudes of 140 kV/cm.…”

“…Please do not adjust margins morphotropic phase boundary (MPB) by Refs 10,32,33 ). This suggests that each RE species has a different influence on the polar-to-nonpolar phase transition temperature (i.e.…”