High DC-Bias Stability and Reliability in BaTiO3-Based Multilayer Ceramic Capacitors: The Role of the Core-Shell Structure and the Electrode.

With the miniaturization of multilayer ceramic capacitors (MLCCs) and the increase of the electric field on a single dielectric layer, dielectric constant DC-bias stability and reliability have gradually aroused attention in the advanced electronics industry. In this study, MLCCs with outstanding DC-bias stability and reliability were prepared by using dielectric ceramic optimization and electrode optimization strategies. The effect of the Dy-Y doping concentration on the microstructure, dielectric properties, and reliability of BaTiO3-based ceramics was investigated. The shell ratio and effective shell doping concentration of the core-shell structure in ceramic grains play important roles in defects and electrical performances. The ceramic with appropriate doping contents shows a dielectric constant of 1800 and a dielectric constant change rate of -17% under a DC field of 4 kV/mm, which was fabricated into prototype MLCCs with different Ni electrodes. MLCCs exhibit outstanding DC-bias stability with a -28% degradation in the dielectric constant under a DC field of 4 kV/mm while possessing a dielectric constant of 2300 and satisfying the EIA X7S specification. Additionally, it was discovered that MLCCs prepared by using fine-size Ni particle electrodes have low electrode roughness and high interfacial Schottky barriers, resulting in better reliability. This study provides promising candidate materials and theoretical references for high-end and high DC-bias stability MLCCs.

An Ion-Enhanced Oncolytic Virus-Like Nanoparticle for Tumor Immunotherapy.

T lymphocytes (T cells) are essential for tumor immunotherapy. However, the insufficient number of activated T cells greatly limits the efficacy of tumor immunotherapy. Herein, we proposed an oncolytic virus-mimicking strategy to enhance T cell recruitment and activation for tumor treatment. We constructed an oncolytic virus-like nanoplatform (PolyIC@ZIF-8) that was degraded in the acidic tumor environment to release PolyIC and Zn2+ . The released PolyIC exhibited an oncolytic virus-like function that induced tumor cell apoptosis and promoted T cell recruitment and activation through a tumor antigen-dependent manner. More importantly, the released Zn2+ not only enhanced T cell recruitment by inducing CXCL9/10/11 expression but also promoted T cell activation to increase interferon-γ (INF-γ) expression by inducing the phosphorylation of ZAP-70 via a tumor antigen-independent manner. This Zn2+ -enhanced oncolytic virus-mimicking strategy provides a new approach for tumor immunotherapy.

Efficient perpendicular magnetization switching by a magnetic spin Hall effect in a noncollinear antiferromagnet.

Current induced spin-orbit torques driven by the conventional spin Hall effect are widely used to manipulate the magnetization. This approach, however, is nondeterministic and inefficient for the switching of magnets with perpendicular magnetic anisotropy that are demanded by the high-density magnetic storage and memory devices. Here, we demonstrate that this limitation can be overcome by exploiting a magnetic spin Hall effect in noncollinear antiferromagnets, such as Mn3Sn. The magnetic group symmetry of Mn3Sn allows generation of the out-of-plane spin current carrying spin polarization collinear to its direction induced by an in-plane charge current. This spin current drives an out-of-plane anti-damping torque providing the deterministic switching of the perpendicular magnetization of an adjacent Ni/Co multilayer. Due to being odd with respect to time reversal symmetry, the observed magnetic spin Hall effect and the resulting spin-orbit torque can be reversed with reversal of the antiferromagnetic order. Contrary to the conventional spin-orbit torque devices, the demonstrated magnetization switching does not need an external magnetic field and requires much lower current density which is useful for low-power spintronics.

Multiphase Engineered BNT-Based Ceramics with Simultaneous High Polarization and Superior Breakdown Strength for Energy Storage Applications.

Dielectric ceramics are crucial for high-temperature, pulse-power energy storage applications. However, the mutual restriction between the polarization and breakdown strength has been a significant challenge. Here, multiphase engineering controlled by the two-step sintering heating rate is adopted to simultaneously obtain a high polarization and breakdown strength in 0.8(0.95Bi0.5Na0.5TiO3-0.05SrZrO3)-0.2NaNbO3 (BNTSZNN) ceramic systems. The coexistence of tetragonal (T) and rhombohedral (R) phases benefits the temperature stability of BNTSZNN ceramics. Increasing the heating rate during sintering reduces the diffusion of SrZrO3 and NaNbO3 into Bi0.5Na0.5TiO3, which results in a high proportion of the R phase and a finer grain size. The overall polarization is enhanced by increasing the proportion of the high-polarization R phase, which is demonstrated using a first-principles method. Meanwhile, the finer grain size enhances the breakdown strength. Following this design philosophy, an ultrahigh Wdis of 5.55 J/cm3 and η above 85% is achieved in BNTSZNN ceramics as prepared with a fast heating rate of 60 °C/min given a simultaneously high polarization of 43 µC/cm2 and high breakdown strength of 350 kV/cm. Variations in the discharge energy density from room temperature to 160 °C are less than 10%. Additionally, such BNTSZNN ceramics exhibit an ultrafast discharge speed with τ0.9 at approximately 60 ns, which shows great potential in pulse-power system applications.

Colossal permittivity behavior and its origin in rutile (Mg1/3Ta2/3)xTi1-xO2.

This work investigates the synthesis, chemical composition, defect structures and associated dielectric properties of (Mg2+, Ta5+) co-doped rutile TiO2 polycrystalline ceramics with nominal compositions of (Mg2+1/3Ta5+2/3) x Ti1-x O2. Colossal permittivity (>7000) with a low dielectric loss (e.g. 0.002 at 1 kHz) across a broad frequency/temperature range can be achieved at x = 0.5% after careful optimization of process conditions. Both experimental and theoretical evidence indicates such a colossal permittivity and low dielectric loss intrinsically originate from the intragrain polarization that links to the electron-pinned [Formula: see text] defect clusters with a specific configuration, different from the defect cluster form previously reported in tri-/pent-valent ion co-doped rutile TiO2. This work extends the research on colossal permittivity and defect formation to bi-/penta-valent ion co-doped rutile TiO2 and elucidates a likely defect cluster model for this system. We therefore believe these results will benefit further development of colossal permittivity materials and advance the understanding of defect chemistry in solids.

Bimetallic Ions Codoped Nanocrystals: Doping Mechanism, Defect Formation, and Associated Structural Transition.

Ionic codoping offers a powerful approach for modifying material properties by extending the selection of potential dopant ions. However, it has been a major challenge to introduce certain ions that have hitherto proved difficult to use as dopants (called "difficult-dopants") into crystal structures at high concentrations, especially through wet chemical synthesis. Furthermore, the lack of a fundamental understanding of how codopants are incorporated into host materials, which types of defect structures they form in the equilibrium state, and what roles they play in material performance, has seriously hindered the rational design and development of promising codoped materials. Here we take In3+ (difficult-dopants) and Nb5+ (easy-dopants) codoped anatase TiO2 nanocrystals as an example and investigate the doping mechanism of these two different types of metal ions, the defect formation, and their associated impacts on high-pressure induced structural transition behaviors. It is experimentally demonstrated that the dual mechanisms of nucleation and diffusion doping are responsible for the synergic incorporation of these two dopants and theoretically evidenced that the defect structures created by the introduced In3+, Nb5+ codopants, their resultant Ti3+, and oxygen vacancies are locally composed of both defect clusters and equivalent defect pairs. These formed local defect structures then act as nucleation centers of baddeleyite- and α-PbO2-like metastable polymorphic phases and induce the abnormal trans-regime structural transition of codoped anatase TiO2 nanocrystals under high pressure. This work thus suggests an effective strategy to design and synthesize codoped nanocrystals with highly concentrated difficult-dopants. It also unveils the significance of local defect structures on material properties.