Highly Responsive Polar Vortices in All-Ferroelectric Heterostructures.

The discovery of polar vortices and skyrmions in ferroelectric-dielectric superlattices [such as (PbTiO)/(SrTiO)] has ushered in an era of novel dipolar topologies and corresponding emergent phenomena. The key to creating such emergent features has generally been considered to be related to counterpoising strongly polar and non-polar materials thus creating the appropriate boundary conditions. This limits the utility these materials can have, however, by rendering (effectively) half of the structure unresponsive to applied stimuli.

Strain-Driven Mixed-Phase Domain Architectures and Topological Transitions in Pb Sr TiO Thin Films.

The potential for creating hierarchical domain structures, or mixtures of energetically degenerate phases with distinct patterns that can be modified continually, in ferroelectric thin films offers a pathway to control their mesoscale structure beyond lattice-mismatch strain with a substrate. Here, it is demonstrated that varying the strontium content provides deterministic strain-driven control of hierarchical domain structures in Pb Sr TiO  solid-solution thin films wherein two types, c/a and a /a , of nanodomains can coexist. Combining phase-field simulations, epitaxial thin-film growth, detailed structural, domain, and physical-property characterization, it is observed that the system undergoes a gradual transformation (with increasing strontium content) from droplet-like a /a  domains in a c/a domain matrix, to a connected-labyrinth geometry of c/a domains, to a disconnected labyrinth structure of the same, and, finally, to droplet-like c/a domains in an a /a  domain matrix.

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.

Probing Metastable Domain Dynamics Automated Experimentation in Piezoresponse Force Microscopy.

The dynamics of complex topological defects in ferroelectric materials is explored using automated experimentation in piezoresponse force microscopy. Specifically, a complex trigger system (, "FerroBot") is employed to study metastable domain-wall dynamics in PbSrTiO thin films. Several regimes of superdomain wall dynamics have been identified, including smooth domain-wall motion and significant reconfiguration of the domain structures.

Resonant domain-wall-enhanced tunable microwave ferroelectrics.

Ordering of ferroelectric polarization and its trajectory in response to an electric field are essential for the operation of non-volatile memories, transducers and electro-optic devices. However, for voltage control of capacitance and frequency agility in telecommunication devices, domain walls have long been thought to be a hindrance because they lead to high dielectric loss and hysteresis in the device response to an applied electric field. To avoid these effects, tunable dielectrics are often operated under piezoelectric resonance conditions, relying on operation well above the ferroelectric Curie temperature, where tunability is compromised.

Intrinsic Two-Dimensional Ferroelectricity with Dipole Locking.

Out-of-plane ferroelectricity with a high transition temperature in ultrathin films is important for the exploration of new domain physics and scaling down of memory devices. However, depolarizing electrostatic fields and interfacial chemical bonds can destroy this long-range polar order at two-dimensional (2D) limit. Here we report the experimental discovery of the locking between out-of-plane dipoles and in-plane lattice asymmetry in atomically thin In_{2}Se_{3} crystals, a new stabilization mechanism leading to our observation of intrinsic 2D out-of-plane ferroelectricity.

Pyroelectric energy conversion with large energy and power density in relaxor ferroelectric thin films.

The need for efficient energy utilization is driving research into ways to harvest ubiquitous waste heat. Here, we explore pyroelectric energy conversion from low-grade thermal sources that exploits strong field- and temperature-induced polarization susceptibilities in the relaxor ferroelectric 0.68Pb(MgNb)O-0.

Large polarization gradients and temperature-stable responses in compositionally-graded ferroelectrics.

A range of modern applications require large and tunable dielectric, piezoelectric or pyroelectric response of ferroelectrics. Such effects are intimately connected to the nature of polarization and how it responds to externally applied stimuli. Ferroelectric susceptibilities are, in general, strongly temperature dependent, diminishing rapidly as one transitions away from the ferroelectric phase transition (T).