Rong Ma

Relaxor ferroelectric 0.9BaTiO3–0.1Bi(Zn0.5Zr0.5)O3 ceramic capacitors with high energy density and temperature stable energy storage properties

A relaxor ferroelectric ceramic for high energy storage applications based on 0.9BaTiO3–0.1Bi(Zn0.5Zr0.5)O3 (0.9BT–0.1BZZ) was successfully fabricated via a conventional solid-state method. The sintered samples have a perovskite structure with a pseudocubic phase, showing a moderate dielectric constant (500–2000), low dielectric loss (tan δ < 0.15) and highly diffusive and dispersive relaxor-like behavior. The weak dielectric nonlinearity exhibits a dielectric constant change of ∼10% as the bias electric field increases from 0 kV cm−1 to 40 kV cm−1. Extra slim polarization–electric field loops accompanying the slow decrease of breakdown strength from 266.5 kV cm−1 to 217.7 kV cm−1 are observed in a measured temperature range of 30–150 °C. A maximum energy density of 2.46 J cm−3 was obtained at the electric field of 264 kV cm−1 close to the breakdown strength at ambient temperature. Temperature stability of both energy density and energy efficiency exists in a wide temperature range, which makes BT–BZZ ceramics promising candidates for high power electric applications.

Tuning conductivity and magnetism of CuFe2O4 via cation redistribution

Copper ferrite polycrystalline samples with different cation distributions are prepared via different thermal treatments. Combined studies including X-ray diffraction, PPMS, Mossbauer spectroscopy, and complex impedance spectroscopy show both conductivity and magnetism keep increasing, accompanied by an obvious phase transition from tetragonal symmetry (I41/amd) to cubic symmetry (Fdm) as Cu2+ ions migrate from Oh sites to Td sites. The changes of structural, electrical and magnetic properties due to the cation redistribution are also investigated by spin-polarized density functional theory. The simulated results indicate that the semiconducting band structure gradually transforms into a metallic band structure as Cu2+ ions migrate from Oh sites to Td sites. The conductivity and magnetism will increase during the same process, which matches well with the experimental observations. This work demonstrates that the cation redistribution in copper ferrite is effective in controlling both conductivity and magnetism, which can be further exploited in applications using interacting electron/spin systems.

Multifunctional hydrogel enables extremely simplified electrochromic devices for smart windows and ionic writing boards

A much simplified electrochromic structure is designed based on a multifunctional ionic hydrogel. The three-layered structure exhibits significant color change with large transmittance modulation and high coloration efficiency. Moreover, an ionic writing board is developed with the hydrogel to realize the first rewritable electrochromic display.

Highly Stable In-Plane Microwave Magnetism in Flexible Li0.35Zn0.3Fe2.35O4(111) Epitaxial Thin Films for Wearable Devices

With the advances in artificial intelligence and communication technologies, flexible microwave magnetic materials have become essential for flexible microwave detectors, wearable microwave sensors, and flexible spintronics. Here, a highly stable in-plane (IP) ferromagnetic resonance (FMR) and a tunable out-of-plane (OOP) FMR character are demonstrated in the flexible microwave magnetic Li0.35Zn0.3Fe2.35O4 (LZFO) (111) epitaxial thin films under external mechanical bending. Both the IP FMR line width and resonance field ( Hr) are basically unchanged when the sample was bent under an external tensile or compressive bending strain and deformation. However, the OOP FMR spectra (including Hr and absorption peak) could be tuned by mechanical bending, i.e., the LZFO sample possesses two OOP FMR absorption peaks at an external bending curvature. Meanwhile, excellent mechanical antifatigue and mechanical retention characteristics have also been obtained in the LZFO sample. The highly stable IP and the tunable OOP FMR spectra in the same LZFO sample with excellent mechanical antifatigue character have a promising prospect in microwave magnetic devices and flexible spintronics.

Thickness-modulated anisotropic ferromagnetism in Fe-doped epitaxial HfO2 thin films

Epitaxial tetragonal Fe-doped Hf0.95Fe0.05O2 (FHO) thin films with various thicknesses were deposited on (001)-oriented NdCaAlO4 (NCAO) substrates by using a pulsed laser deposition (PLD) system. The crystal structure and epitaxial nature of the FHO thin films were confirmed by typical x-ray diffraction (XRD) θ–2θ scan and reciprocal space mapping (RSM). The results indicate that two sets of lattice sites exist with two different crystal orientations [(001) and (100)] in the thicker FHO thin films. Further, the intensity of the (100) direction increases with the increase in thicknesses, which should have a significant effect on the anisotropic magnetization of the FHO thin films. Meanwhile, all the FHO thin films possess a tetragonal phase structure. An anisotropy behavior in magnetization has been observed in the FHO thin films. The anisotropic magnetization of the FHO thin films is slowly weakened as the thickness increases. Meanwhile, the saturation magnetization (Ms) of both in-plane and out-of-plane ...

Effect of thickness-dependent crystal mosaicity and chemical defect on electric properties in yttrium-stabilized epitaxial HfO2 thin films

Epitaxial pseudo cubic yttrium-stabilized Y0.05Hf0.95O2 (YHO) thin films with bottom electrode layers of Pr0.5Sr0.5CoO3 were deposited on (001)-oriented LaAlO3 (LAO) substrates by using the pulsed laser deposition system. The crystal structure and thickness of the films were confirmed by θ–2θ scan and X-ray reflectivity via X-ray diffraction technology, respectively. Reciprocal space mapping (RSM) was performed to clarify the microstructure of the epitaxial YHO films affected by LAO substrates, and the result of symmetric RSMs revealed that the crystal mosaicity of the YHO films increases with the increasing film thicknesses. Moreover, the dominant conduction mechanisms of all the YHO films were ohmic conduction in the low electric field. At a high applied electric field, the YHO-5.4 nm film was determined by the space-charge-limited current behavior, while the samples of the YHO-9.8 nm and YHO-19.2 nm films were determined by ohmic conduction. The temperature-dependent I–V characteristics of the YHO film...