Search for: All records

Antiferroelectric (Pb0.87Sr0.05Ba0.05La0.02)(Zr0.52Sn0.40Ti0.08)O3 thin film capacitors were fabricated for dielectric energy storage. Thin films with excellent crystal quality (FWHM 0.021°) were prepared on (100) SrRuO3/SrTiO3 substrates by pulsed laser deposition. The out-of-plane lattice constant of the thin film was 4.110 ± 0.001 Å. An average maximum recoverable energy storage density, 88 ± 17 J cm−3 with an efficiency of 85% ± 6% at 1 kHz and 80 ± 15 J cm−3 with an efficiency of 91% ± 4% at 10 kHz, was achieved at room temperature. The capacitor was fatigue resistant up to 106 cycles at an applied electric field of 2 MV cm−1. These properties are linked to a low level of hysteresis and slow polarization saturation. PbZrO3-derived oxide thin film capacitors are promising for high efficiency and low loss dielectric energy storage applications. 

The effect of an electric field on local domain structure near a 24° tilt grain boundary in a 200 nm-thick Pb(Zr_0.2Ti_0.8)O₃bi-crystal ferroelectric film was probed using synchrotron nanodiffraction. The bi-crystal film was grown epitaxially on SrRuO₃-coated (001) SrTiO₃24° tilt bi-crystal substrates. From the nanodiffraction data, real-space maps of the ferroelectric domain structure around the grain boundary prior to and during application of a 200 kV cm⁻¹electric field were reconstructed. In the vicinity of the tilt grain boundary, the distributions of densities ofc-type tetragonal domains with thecaxis aligned with the film normal were calculated on the basis of diffracted intensity ratios ofc- anda-type domains and reference powder diffraction data. Diffracted intensity was averaged along the grain boundary, and it was shown that the density ofc-type tetragonal domains dropped to ∼50% of that of the bulk of the film over a range ±150 nm from the grain boundary. This work complements previous results acquired by band excitation piezoresponse force microscopy, suggesting that reduced nonlinear piezoelectric response around grain boundaries may be related to the change in domain structure, as well as to the possibility of increased pinning of domain wall motion. The implications of the results and analysis in terms of understanding the role of grain boundaries in affecting the nonlinear piezoelectric and dielectric responses of ferroelectric materials are discussed. 

The rapid development of computation power and machine learning algorithms has paved the way for automating scientific discovery with a scanning probe microscope (SPM). The key elements toward operationalization of the automated SPM are the interface to enable SPM control from Python codes, availability of high computing power, and development of workflows for scientific discovery. Here, we build a Python interface library that enables controlling an SPM from either a local computer or a remote high-performance computer, which satisfies the high computation power need of machine learning algorithms in autonomous workflows. We further introduce a general platform to abstract the operations of SPM in scientific discovery into fixed-policy or reward-driven workflows. Our work provides a full infrastructure to build automated SPM workflows for both routine operations and autonomous scientific discovery with machine learning. 

In many commercially utilized ferroelectric materials, the motion of domain walls is an important contributor to the functional dielectric and piezoelectric responses. This paper compares the temperature dependence of domain wall motion for BaTiO3 ceramics with different grain sizes, point defect concentrations, and formulations. The grain boundaries act as significant pinning points for domain wall motion such that fine-grained materials show smaller extrinsic contributions to the properties below the Curie temperature and lower residual ferroelectric contributions immediately above the Curie temperature. Oxygen vacancy point defects make a modest change in the extrinsic contributions of undoped BaTiO3 ceramics. In formulated BaTiO3, extrinsic contributions to the dielectric response were suppressed over a wide temperature range. It is believed this is due to a combination of reduced grain size, the existence of a core-shell microstructure, and a reduction in domain wall continuity over the grain boundaries. 

Flexoelectricity offers an energy harvesting alternative to piezoelectric materials. Although flexoelectricity is generally weak in most materials, recent findings show that bending a semiconductor with insulating barrier layers could induce a significantly enhanced flexoelectric response. We call this effect the Space Charge Induced Flexoelectric (SCIF) effect. This study explores the induced polarization resulting from free charge redistribution in a doped silicon beam. To understand the underlying physics, a 3D numerical model combining flexoelectric principles and the drift-diffusion theory of semiconduction was developed. The effective flexoelectric coefficient was computed by comparing the differential charge accumulation at the top and bottom of the beam and compared that with the experimental observations.