Unfolding grain size effects in barium titanate ferroelectric ceramics

Grain size effects on the physical properties of polycrystalline ferroelectrics have been extensively studied for decades; however there are still major controversies regarding the dependence of the piezoelectric and ferroelectric properties on the grain size. Dense BaTiO3 ceramics with different grain sizes were fabricated by either conventional sintering or spark plasma sintering using micro- and nano-sized powders. The results show that the grain size effect on the dielectric permittivity is nearly independent of the sintering method and starting powder used. A peak in the permittivity is observed in all the ceramics with a grain size near 1μm and can be attributed to a maximum domain wall density and mobility. The piezoelectric coefficient d33 and remnant polarization Pr show diverse grain size effects depending on the particle size of the starting powder and sintering temperature. This suggests that besides domain wall density, other factors such as back fields and point defects, which influence the domain wall mobility, could be responsible for the different grain size dependence observed in the dielectric and piezoelectric/ferroelectric properties. In cases where point defects are not the dominant contributor, the piezoelectric constant d33 and the remnant polarization Pr increase with increasing grain size

Synthesis, physics, and applications of ferroelectric nanomaterials

Improvement of both solution and vapor-phase synthetic techniques for nanoscale ferroelectrics has fueled progress in fundamental understanding of the polar phase at reduced dimensions, and this physical insight has pushed the boundaries of ferroelectric phase stability and polarization switching to sub-10 nm dimensions. The development and characterization of new ferroelectric nanomaterials has opened new avenues toward future nonvolatile memories, devices for energy storage and conversion, biosensors, and many other applications. This prospective will highlight recent progress on the synthesis, fundamental understanding, and applications of zero- and one-dimensional ferroelectric nanomaterials and propose new directions for future study in all three areas

Cellulose-based magnetoelectric composites

Since the first magnetoelectric polymer composites were fabricated more than a decade ago, there has been a reluctance to use piezoelectric polymers other than poly(vinylidene fluoride) and its copolymers due to their well-defined piezoelectric mechanism and high piezoelectric coefficients that lead to superior magnetoelectric coefficients of > 1 V.cm−1 Oe−1. This is the current situation despite the potential for other piezoelectric polymers, such as natural biopolymers, to bring unique, added-value properties and functions to magnetoelectric composite devices. Therefore, we demonstrate a cellulose-based magnetoelectric laminate composite that produces considerable magnetoelectric coefficients of 1.5 V.cm−1 Oe−1 at low magnetic fields. Simple solution processing induces alignment of cellulose fibrils, leading to amplification of nanoscale piezoelectric domains and the magnetoelectric coefficient. The magnetoelectric frequency line shape shows a Fano-resonance that is ubiquitous in the field of physics, such as photonics, though never experimentally observed in magnetoelectric composites. This fundamental phenomenon is due to the inherent chemical structure of cellulose and important for understanding the magnetoelectric mechanisms. The work successfully demonstrates the concept of exploring new advances in using biopolymers in magnetoelectric composites, particularly cellulose, which is increasingly employed as a renewable, low-cost, easily processable and degradable material.The authors would like to acknowledge the financial support from the ARC Australian Research Fellowship (A/Prof. Michael Higgins) and ARC DP110104359 and ARC Centre of Excellence for Electromaterials Science (ACES, Project Number CE 140100012), University of Wollongong (UOW) We acknowledge assistance from Yi Du and Long Ren (UOW) for scanning electron microscopy. The authors would also like to acknowledge the FCT - Fundação para a Ciência e Tecnologia -for financial support under project PTDC/EEI-SII/5582/2014 and FCTgrant SFRH/BPD/96227/2013 (PM). SLM thanks financial support from the Basque Government Industry Department under the ELKARTEK Program and the Diputación Foral de Bizkaia for finantial support under the Bizkaia Talent program; European Union’s Seventh Framework Programme; Marie Curie Actions – People; Grant agreement nº 267230. like to acknowledge the FCT - Fundação para a Ciência e Tecnologia - for financial support under project PTDC/EEI - SII/5582/2014 and FCT grant SFRH/BPD/96227/2013 (PM). SLM thanks financial support from the Basque Government Industry Department under the ELKARTEK Program and the Diputación Foral de Bizkaia for finantial support under the Bizkaia Talent program; European Union’s Seventh Framework Programme; Marie Curie Actions – People; Grant agreement nº 267230info:eu-repo/semantics/publishedVersio