Bulk-Rashba Effect with Suppressed Spin Relaxation in a Polar Phase of Bi In O.

The Rashba effect enables control over the spin degree of freedom, particularly in polar materials where the polar symmetry couples to Rashba-type spin splitting. The exploration of this effect, however, has been hindered by the scarcity of polar materials exhibiting the bulk-Rashba effect and rapid spin-relaxation effects dictated by the D'yakonov-Perel mechanism. Here, a polar LiNbO-type R3c phase of Bi In O with x ≈0.

Colossal Electromechanical Response in Antiferroelectric-based Nanoscale Multilayers.

The pursuit of smaller, energy-efficient devices drives the exploration of electromechanically active thin films (<1 µm) to enable micro- and nano-electromechanical systems. While the electromechanical response of such films is limited by substrate-induced mechanical clamping, large electromechanical responses in antiferroelectric and multilayer thin-film heterostructures have garnered interest. Here, multilayer thin-film heterostructures based on antiferroelectric PbHfO and ferroelectric PbHfTiO overcome substrate clamping to produce electromechanical strains >4.

High sound pressure piezoelectric micromachined ultrasonic transducers using sputtered potassium sodium niobate.

This work presents air-coupled piezoelectric micromachined ultrasonic transducers (pMUTs) with high sound pressure level (SPL) under low-driving voltages by utilizing sputtered potassium sodium niobate KNaNbO (KNN) films. A prototype single KNN pMUT has been tested to show a resonant frequency at 106.3 kHz under 4 V with outstanding characteristics: (1) a large vibration amplitude of 3.

Clamping enables enhanced electromechanical responses in antiferroelectric thin films.

Thin-film materials with large electromechanical responses are fundamental enablers of next-generation micro-/nano-electromechanical applications. Conventional electromechanical materials (for example, ferroelectrics and relaxors), however, exhibit severely degraded responses when scaled down to submicrometre-thick films due to substrate constraints (clamping). This limitation is overcome, and substantial electromechanical responses in antiferroelectric thin films are achieved through an unconventional coupling of the field-induced antiferroelectric-to-ferroelectric phase transition and the substrate constraints.

3D Printing and processing of miniaturized transducers with near-pristine piezoelectric ceramics for localized cavitation.

The performance of ultrasonic transducers is largely determined by the piezoelectric properties and geometries of their active elements. Due to the brittle nature of piezoceramics, existing processing tools for piezoelectric elements only achieve simple geometries, including flat disks, cylinders, cubes and rings. While advances in additive manufacturing give rise to free-form fabrication of piezoceramics, the resultant transducers suffer from high porosity, weak piezoelectric responses, and limited geometrical flexibility.

Defect-Induced, Ferroelectric-Like Switching and Adjustable Dielectric Tunability in Antiferroelectrics.

Antiferroelectrics, which undergo a field-induced phase transition to ferroelectric order that manifests as double-hysteresis polarization switching, exhibit great potential for dielectric, electromechanical, and electrothermal applications. Compared to their ferroelectric cousins, however, considerably fewer efforts have been made to understand and control antiferroelectrics. Here, it is demonstrated that the polarization switching behavior of an antiferroelectric can be strongly influenced and effectively regulated by point defects.

Size-Induced Ferroelectricity in Antiferroelectric Oxide Membranes.

Despite extensive studies on size effects in ferroelectrics, how structures and properties evolve in antiferroelectrics with reduced dimensions still remains elusive. Given the enormous potential of utilizing antiferroelectrics for high-energy-density storage applications, understanding their size effects will provide key information for optimizing device performances at small scales. Here, the fundamental intrinsic size dependence of antiferroelectricity in lead-free NaNbO membranes is investigated.

Thin-Film Ferroelectrics.

Over the last 30 years, the study of ferroelectric oxides has been revolutionized by the implementation of epitaxial-thin-film-based studies, which have driven many advances in the understanding of ferroelectric physics and the realization of novel polar structures and functionalities. New questions have motivated the development of advanced synthesis, characterization, and simulations of epitaxial thin films and, in turn, have provided new insights and applications across the micro-, meso-, and macroscopic length scales. This review traces the evolution of ferroelectric thin-film research through the early days developing understanding of the roles of size and strain on ferroelectrics to the present day, where such understanding is used to create complex hierarchical domain structures, novel polar topologies, and controlled chemical and defect profiles.

Exploring the Pb Sr HfO System and Potential for High Capacitive Energy Storage Density and Efficiency.

The hafnate perovskites PbHfO (antiferroelectric) and SrHfO ("potential" ferroelectric) are studied as epitaxial thin films on SrTiO (001) substrates with the added opportunity of observing a morphotropic phase boundary (MPB) in the Pb Sr HfO system. The resulting (240)-oriented PbHfO (Pba2) films exhibited antiferroelectric switching with a saturation polarization ≈53 µC cm at 1.6 MV cm , weak-field dielectric constant ≈186 at 298 K, and an antiferroelectric-to-paraelectric phase transition at ≈518 K.

Ultrahigh capacitive energy density in ion-bombarded relaxor ferroelectric films.

Dielectric capacitors can store and release electric energy at ultrafast rates and are extensively studied for applications in electronics and electric power systems. Among various candidates, thin films based on relaxor ferroelectrics, a special kind of ferroelectric with nanometer-sized domains, have attracted special attention because of their high energy densities and efficiencies. We show that high-energy ion bombardment improves the energy storage performance of relaxor ferroelectric thin films.

Nanomechanical responses of human hair.

Here we report the first ever studies on nanomechanical properties e.g., nanohardness and Young׳s modulus for human hair of Indian origin.