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. Intrinsic point defects created by ion bombardment reduce leakage, delay low-field polarization saturation, enhance high-field polarizability, and improve breakdown strength. We demonstrate energy storage densities as high as ~133 joules per cubic centimeter with efficiencies exceeding 75%. Deterministic control of defects by means of postsynthesis processing methods such as ion bombardment can be used to overcome the trade-off between high polarizability and breakdown strength.

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Integrating the diverse functionalities of complex oxides into semiconductor [1-7] and flexible [8-12] electronics is a major technological challenge that has motivated extensive work. But despite considerable effort, the structural, chemical, and thermal mismatches between such substrates and complex-oxide materials often yield films with considerably worse crystal quality than that attained on single-crystal perovskite substrates. Alternative strategies for hetero-integration via substrate release and transfer, mimicking the fabrication processes of van-der-Waals heterostructures, [13-15] are just now beginning to yield single-crystal oxide films on arbitrary substrates, [16-21] thus circumventing the constraints of epitaxial growth. Moreover, these detached films no longer experience mechanical constraint from the substrate, giving more flexibility in structural manipulation and heterostructure assembly. Strain control over the lattice structure is particularly impactful in ferroelectrics where the polarization is directly connected to structural distortions. [22,23] In thin films, strain can define the optimal operating temperature regime [24-26] or domain configuration [27-29] that will boost electro-mechanical or thermal functionalities, Strain engineering in perovskite oxides provides for dramatic control over material structure, phase, and properties, but is restricted by the discrete strain states produced by available high-quality substrates. Here, using the ferroelectric BaTiO 3 , production of precisely strain-engineered, substratereleased nanoscale membranes is demonstrated via an epitaxial lift-off process that allows the high crystalline quality of films grown on substrates to be replicated. In turn, fine structural tuning is achieved using interlayer stress in symmetric trilayer oxide-metal/ferroelectric/oxide-metal structures fabricated from the released membranes. In devices integrated on silicon, the interlayer stress provides deterministic control of ordering temperature (from 75 to 425 °C) and releasing the substrate clamping is shown to dramatically impact ferroelectric switching and domain dynamics (including reducing coercive fields to <10 kV cm −1 and improving switching times to <5 ns for a 20 µm diameter capacitor in a 100-nm-thick film). In devices integrated on flexible polymers, enhanced room-temperature dielectric permittivity with large mechanical tunability (a 90% change upon ±0.1% strain application) is demonstrated. This approach paves the way toward the fabrication of ultrafast CMOS-compatible ferroelectric memories and ultrasensitive flexible nanosensor devices, and it may also be leveraged for the stabilization of novel phases and functionalities not achievable via direct epitaxial growth. Perovskite ABO 3 oxides can display an immense number of phases and functions by merely changing the A-and B-site cations. Even within a single chemistry, multiple phases can be in competition, and their stability can be tuned statically by fixing The ORCID identification number(s) for the ...

Ferroelectric semiconductors are rare materials with both spontaneous polarizations and visible light absorptions that are promising for designing functional photoferroelectrics, such as optical switches and ferroelectric photovoltaics. The emerging halide perovskites with remarkable semiconducting properties also have the potential of being ferroelectric, yet the evidence of robust ferroelectricity in the typical three-dimensional hybrid halide perovskites has been elusive. Here, we report on the investigation of ferroelectricity in all-inorganic halide perovskites, CsGeX 3 , with bandgaps of 1.6 to 3.3 eV. Their ferroelectricity originates from the lone pair stereochemical activity in Ge (II) that promotes the ion displacement. This gives rise to their spontaneous polarizations of ~10 to 20 μC/cm 2 , evidenced by both ab initio calculations and key experiments including atomic-level ionic displacement vector mapping and ferroelectric hysteresis loop measurement. Furthermore, characteristic ferroelectric domain patterns on the well-defined CsGeBr 3 nanoplates are imaged with both piezo-response force microscopy and nonlinear optical microscopic method.

Using pulsed ferroelectric measurements, we probe switching dynamics in multiferroic BiFeO 3 , revealing low-ns switching times and a clear pathway to sub-ns switching. Our data is well described by a nucleation and growth model, which accounts for the various timescales in the switching process, namely (1) the ferroelectric polarization switching (bound-charge) dynamics and (2) the RC-limited movement of free charge in the circuit. Our model shows good agreement with observed data and begins to bridge the gap between experiment and theory, indicating pathways to study ferroelectric switching on intrinsic timescales.