Search

In this work, the resistive switching and electrical-control of magnetization in Pt/CoFe2O4/Nb:SrTiO3 heterostructures have been investigated. The films exhibit a classic bipolar resistive switching effect with a maximum switch ratio of about 5 × 103 and good anti-fatigue performance. Associated with resistive switching, the saturated magnetization of the thin film at high resistance state is found to be larger than that at low resistance state. Meanwhile, polarized neutron reflectivity of the thin film under different resistance states was in situ measured. The results reveal that the interfacial migration of oxygen vacancies driven by an applied electric field plays an important role in the modulation of resistive and magnetism of CoFe2O4 resistive switching devices. [ABSTRACT FROM AUTHOR]

• Investigation of magnetic and electronic properties of PBMO thin films by modulating oxygen vacancies. • Correlation between oxygen vacancy content, lattice structure, and physical properties in PBMO films observed by XRD, STEM, and PNR analyses. • Quantitatively depth profile of the oxygen stoichiometry and corresponding magnetization of PBMO thin films by PNR. In this work, the magnetic and electronic transport properties of the epitaxial Pr 0.5 Ba 0.5 MnO 3-δ (PBMO) thin films via the modulation of the oxygen vacancies have been investigated. PBMO thin films were fabricated by pulsed laser deposition (PLD) at different oxygen ambient pressures (20, 50, 70, and 250 mTorr). From the XRD and STEM measurements, the oxygen vacancies content in the film increases with the decrease of growth pressure, leading to an expansion of the out-of-plane lattice constant of the film. The PNR (Polarized Neutron Reflectometry) was employed for a precise magnetization and oxygen stoichiometry depth profile of the PBMO thin films and further quantitatively characterize the oxygen vacancies' content of the films. Thus, an increasing number of oxygen vacancies suppress the double exchange interaction and carriers hopping are suppressed, resulting in a significant increase in resistivity, as well as a decrease in saturation magnetization and ferromagnetic Curie temperature. [ABSTRACT FROM AUTHOR]

Bismuth sodium titanate (BNT)‐based lead‐free piezoceramics are promising for replacing lead‐based piezoceramics in piezoelectric actuators due to their large strains. However, achieving low‐hysteresis large‐strain BNT‐based ceramics over a broad temperature range is challenging, owing to the complexity of the composition design and phase transformation. Herein, a lead‐free relaxor‐ferroelectric (1−x)Bi0.47Na0.47Ba0.06TiO3‐xK0.47Na0.47Li0.06Nb0.99Sb0.01O2.99 system (BNBT‐KNLNS) near the morphotropic phase boundary (MPB), achieved by phase‐field simulations and rational composition design (i.e., BNBT with the MPB as the base and the ferroelectric phase of KNLNS as the dopant) is reported. This ceramic exhibits large strains (0.32–0.51%) and low strain hysteresis (11.1–59.9%) over a wide temperature range (25–125 °C), outperforming many state‐of‐the‐art lead‐free piezoceramics. A small fraction of ferroelectric states embedded in the relaxor matrix is experimentally observed, where these states act as seeds, facilitating the reversible relaxor‐to‐ferroelectric transition. In addition, the MPB composition with low energy barriers yields large strain responses, owing to the easy polarization reversal and extension. Consequently, low‐hysteresis large strains are obtained over a broad temperature range. This work provides a novel design route for discovering high‐performance piezoceramics for actuator applications. [ABSTRACT FROM AUTHOR]

Epitaxial (Pr0.5Ba0.5MnO3)1−x:(CeO2)x (PBMO:CeO2, x = 0, 10%, 20%, 35%, and 50% stands for the molar ratio of the CeO2 secondary phase) vertically aligned nanocomposite (VAN) thin films were successfully fabricated on single crystalline (001) (La,Sr)(Al,Ta)O3 substrates by pulsed laser deposition. With increasing x, a structural transition induced by the vertical strain from the CeO2 secondary phase was observed at 20% ≤x≤ 35% by reciprocal space mapping. What's more, it is not only the enhancement of magnetoresistance that was observed but also the increasing magnetization. The maximum magnetization and magnetoresistance were achieved at x = 35%, which are almost 4.7 times (at 20 K) and 1.6 times (at 110 K) as high as those at x = 0%, respectively. Such great enhancement of magnetization can be attributed to the vertical strain induced structural transition. Our research indicates that the structural transition induced by the introduction of secondary phase CeO2 plays an important role in improving the magnetic and transport properties of VAN thin films. [ABSTRACT FROM AUTHOR]

We report a giant strain (0.72%) with a low degree of hysteresis ( ca . 36.2%) and a giant S max / E max ratio (916 pm V −1 , S max and E max denote the maximum strain and the corresponding electric field, respectively) for lead-free (1− x )(0.8Bi 0.5 Na 0.5 TiO 3 -0.2Bi 0.5 K 0.5 TiO 3 )- x Sr 0.8 Bi 0.1 □ 0.1 Ti 0.8 Zr 0.2 O 2.95 piezoceramics with x = 0.06. The giant strain originates from a reversible transition between the ergodic relaxor and ferroelectric states under applied electric fields. A-site vacancies (V A ) and oxygen vacancies (V O ), deliberately introduced to the system, induce a randomly distributed local polarization field. The local field induces embryonic polarization domains that have a broad distribution of maturity and thus smears the transition between the ferroelectric and relaxor states. This leads to a narrow hysteresis loop. The poling field required for the relaxor-to-ferroelectric transition is reduced significantly, due to the remanent ferroelectric phase at zero field acting as the seed, and the point defects synergistically facilitating the nucleation and growth of the ferroelectric phase. Our work provides a novel route for designing piezoelectric materials with both a giant strain and a narrow hysteresis for practical actuator applications. [ABSTRACT FROM AUTHOR]

Keywords: lead-free piezoceramics; morphotropic phase boundaries; phase-field simulations; piezoresponse force microscopy; strain EN lead-free piezoceramics morphotropic phase boundaries phase-field simulations piezoresponse force microscopy strain 1 1 1 08/11/22 20220808 NES 220808 B Lead-Free Piezoceramics b In article number 2202307, Linglong Li, Dong Wang, and Xiaojie Lou, and co-workers report a computationally aided composition design for discovering high-performance lead-free perovskite piezomaterials. Lead-free piezoceramics, morphotropic phase boundaries, phase-field simulations, piezoresponse force microscopy, strain The obtained bismuth sodium titanate-based relaxor-ferroelectric ceramic demonstrates low-hysteresis large strains over a wide range of temperatures, which holds great promise for practical applications of actuator devices operating at room to high temperatures. [Extracted from the article]

As a member of the ternary metal oxide family, nickel cobaltite is considered as a promising electrode material. This is due to its high theoretical capacity, low diffusional resistance to protons, ease of electrolyte penetration, superior ionic/electronic conductivity and higher electrochemical activity compared to single metallic oxides such as NiO or Co 3 O 4 . However, NiCo 2 O 4 's relatively low electrical conductivity and its tendency to pulverize due to the volume changes experienced during the charge–discharge process remain a pressing issue to be solved. Here we demonstrate a simple co-precipitation and calcination routine to graft ultrathin NiCo 2 O 4 nanosheets onto highly-ordered mesoporous carbon CMK-3 to form a new mesoporous-nanosheet structure which can accommodate stresses induced by volume changes and provide favourable conducting paths. The material exhibits a high specific surface area and excellent electrochemical performance, which can be ascribed to the ultrathin NiCo 2 O 4 nanosheets and the interconnected conductive network of the mesoporous matrix. The nanosheets and the inner channels of CMK-3 are more beneficial to the diffusion of Li + while the interconnected conductive network favours fast electron conduction. [ABSTRACT FROM AUTHOR]

In this work, we report the synthesis of one-dimensional (1-D) hierarchical NiO nanosheets covering bamboo-like amorphous CNT composites (NiO@CNT) via a facile and a low-cost solution route based on sulfonated polymeric nanotubes (PNTs) used simultaneously as both, a template, and a source of nano-structured carbon derived by a low-temperature thermal carbonization treatment. The electrochemical performance of the NiO@CNT composite electrode indicate that this novel hybrid nanostructure is potentially capable of delivering excellent reversible capacity when used as an anode material in a lithium-ion battery (LIB). A large discharge capacity of 1034 mAh g −1 is delivered by the NiO@CNT composite even after 300 cycles at a relatively high current density of 800 mA g −1 , with an average coulombic efficiency of 98.1%. A significant achievement in the reversible capacity of the NiO@CNT composite is attributed to the outstanding nanostructure resulting in synergistic effects of the hollow amorphous CNT backbone and ultrathin NiO nanosheets. Furthermore, the generic solution method to fabricate 1-D metal oxides@amorphous CNT nanostructures, developed in this work, is expected to have a wide range of applications in improving the properties of transition metal oxides. [ABSTRACT FROM AUTHOR]

Abstract: Self-assembled ZnO/Ag nanocomposite thin films have been fabricated on Si (111) by a reactive radio-frequency magnetron sputtering system. Microstructural characterizations by transmission electron microscopy indicated that the Ag nano-particles are uniformly embedded into the ZnO films. The intensity of resonance Raman scattering spectra is significantly enhanced with the increase of Ag contents in the film, compared with the pure ZnO film, while the intensity of reflection spectrum is reduced, which is assigned to the interaction between localized Surface Plasmons in the Ag nanoparticles and the incident light. [Copyright &y& Elsevier]

Nanoscaled HfO 2 -based ferroelectric thin films are a favored candidate for the integration of next-generation memory and logic devices. The unique advantage is that the ferroelectric polarization becomes more robust than the traditional perovskite ferroelectrics when the size is reduced. Understanding and controlling the ferroelectricity requires high-quality epitaxial thin films to explore intrinsic ferroelectric mechanism and evaluate device applications. Here, we report a semicoherent growth of ITO as a bottom electrode that enables genuine ultrathin epitaxial films of Si-doped HfO 2 on YSZ [001]/[110]/[111] substrates. The deposited films, which are under epitaxial compressive strain, display large ferroelectric polarization values up to 42 μC/cm2 and do not need wake-up cycling. Structural characterization reveals the presence of crystalline domains with short axes of the tetragonal structure oriented perpendicular to the substrate. Using piezoforce microscopy, polar domains can be written and read and can be reversibly switched with a phase change of 180o. Ferroelectric polarization can be controlled by ITO surface polarity which can easily exploit the interfacial valance mismatch to influence the electrostatic potential across the interface. These findings have implications for our understanding of ferroelectric switching and offer easy method to manipulate domain reversal state in HfO 2 -based ferroelectric materials. Image, graphical abstract [ABSTRACT FROM AUTHOR]