内田 寛

Ferroelectric hafnium and zirconium oxides have undergone rapid scientific development over the last decade, pushing them to the forefront of ultralow-power electronic systems. Maximizing the potential application in memory devices or supercapacitors of these materials requires a combined effort by the scientific community to address technical limitations, which still hinder their application. Besides their favorable intrinsic material properties, HfO2–ZrO2 materials face challenges regarding their endurance, retention, wake-up effect, and high switching voltages. In this Roadmap, we intend to combine the expertise of chemistry, physics, material, and device engineers from leading experts in the ferroelectrics research community to set the direction of travel for these binary ferroelectric oxides. Here, we present a comprehensive overview of the current state of the art and offer readers an informed perspective of where this field is heading, what challenges need to be addressed, and possible applications and prospects for further development.

Abstract Aiming at applications of ferroelectric and optical devices, we investigated the fabrication of one-axis-oriented lead zirconate titanate Pb(Zr,Ti)O₃ (PZT) thin films on glass substrates with a processing temperature below the glass-transition point of the substrate. Chemical solution deposition (CSD)-derived PZT thin films with a preferential crystal orientation of (00l)/(h00)PZT were grown on an ITO/glass substrate with a crystalline buffer layer of calcium niobate Ca₂Nb₃O₁₀ (ns-CN). This ns-CN buffer layer lowered the crystallization temperature of the CSD-derived thin films, resulting in crystalline PZT thin films with one-axis (00l) orientation and ferroelectricity of P_r = 4 μC cm⁻² deposited on transparent glass substrates at a crystallization temperature of 500 °C.

Epitaxial films of (K,Na,Li)NbO3 with 10 over line m thickness and various Li contents were fabricated at 240 degrees C on (001)La:SrTiO3 substrates by a hydrothermal method, and their crystal structures and piezoelectric properties were investigated. The film thickness was controlled by varying the deposition time (up to 3.5 h) and the number of deposition cycles. Scanning electron microscopy observations showed that dense thick films were formed. X-ray diffraction (XRD) measurements showed that {001}c-oriented epitaxial films were deposited, and the outof-plane lattice constant changed with an increase in the nominal composition A = [LiOH]/([KOH] + [NaOH] + [LiOH]) of the alkaline source solution. High-temperature XRD measurement revealed that with an increase in A, the Curie temperature increased, while the orthorhombic-tetragonal phase transition temperature decreased from 210 to 120 degrees C. These structural changes indicate that the Li content in the thick films can be controlled by varying A. The dielectric properties depend on the measurement frequency, and the minimum relative dielectric permittivity at all frequencies was observed at A = 0.02. Curves of field-induced strain vs. electric field showed that the maximum normalized strain of Smax/Emax = 40 pm/V was observed at A = 0.03, indicating that Li substitution is an effective way to improve the piezoelectricity of the hydrothermally deposited (K,Na)NbO3 thick films. Interestingly, all thick films exhibited a piezoelectric response despite the applied electric field being lower than the coercive field. Moreover, the Smax/Emax value did not change significantly with an increasing applied electric field. These results suggest that the hydrothermally deposited (K,Na,Li)NbO3 thick films adopt a selfpolarized state without poling treatment. (c) 2022 The Ceramic Society of Japan. All rights reserved.

The aqueous extract of the leaves of Odontonema strictum (OSM) is used in folk medicine for its antihypertensive properties, and it contains a wide range of secondary metabolites, mostly polyphenols such as verbascoside and isoverbascoside, which could play a major role in the preparation of silver nanoparticles. In this study, we aimed to prepare AgNPs for the first time using the OSM leaf extract (OSM-AgNPs) to investigate their free radical-scavenging potency against 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydrogen peroxide (H2O2). Dynamic light scattering (DLS), UV/Vis, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS) were used to characterize the OSM-AgNPs. With a size around 100 nm and a ζ-potential of -41.1 mV, OSM-AgNPs showed a good stability and a better colloidal property due to electrostatic repulsion and the dispersity. The strong absorption peak at 3 keV in the EDX spectra indicated that silver was the major constituent. Additionally, the existence of silver atoms was confirmed by the Ag 3d5/2 peak around 367 eV in the XPS spectra. IC50 values of 116 μg/mL and 4.4 μg/mL were obtained for the scavenging activities of DPPH and H2O2, respectively. The synthetic OSM-AgNPs can be further exploited as potential antioxidant agents.