Search

In this work, the magnetocaloric effect in Ni50Mn36In5Sb9 alloy was increased by more than 50% through directional solidification, and the magnetic entropy change increased to 36.2 J kg−1 K−1 under the field of 5 T. The calculated results of differential scanning calorimetry curves confirmed the enhanced entropy change, which also increased from 29.7 to 40.7 J kg−1 K−1. Moreover, first-principles calculations show that the surface formation energy along the L21 (220) plane is the lowest at room temperature, and it is easy to form and undergo martensitic transformation from the (220) crystal plane. Directional solidification causes the alloy to grow basically toward the (220) crystal plane, improve atomic ordering, reduce grain boundaries, and increase grain size. Thereby, the magnetic entropy change is enhanced. [ABSTRACT FROM AUTHOR]

Liquid-liquid phase separation (LLPS) phenomenon are widely recognized to be of vital importance for physics, materials science, and biology. It is highly desired to develop powerful tools to study the LLPS behavior and related physical mechanisms. For this purpose, a phase-field method was developed here which combines the Cahn-Hilliard diffusion equation and the Navier-Stokes equation. The morphological evolution of LLPS behavior with the change in composition was comprehensively investigated under a prototypical ternary theoretical phase diagram. The phase-field simulation results indicated that the microstructural evolution was controlled by the phase diagram and driven by the coupling of diffusion and gravity effect. Moreover, the intermediate morphological microstructures and corresponding interfacial properties during LLPS could be tuned by selecting different composition change pathways. Furthermore, gravity-dependent density overturning and consequent Rayleigh-Taylor instability were observed in a unique LLPS process, demonstrating that the proposed model can capture the critical features of LLPS phenomenon. [ABSTRACT FROM AUTHOR]

Dielectric capacitors, as one of the important electronic devices, are widely used in various fields. However, most ferroelectric capacitors with high energy storage density require excessively high electric fields. In this work, we have prepared 0.9(Bi0.5Na0.5)0.7Sr0.3TiO3-0.1 Bi(Mg2/3Nb1/3)O3 relaxor ferroelectric ceramics with different BaZrO3 doping levels. A high energy storage (Wr) of 4.07 J/cm3 and efficiency (η) of 91% are simultaneously obtained in 0.94[0.9(Bi0.5Na0.5)0.7Sr0.3TiO3-0.1 Bi(Mg2/3Nb1/3)O3]-0.06BaZrO3 ceramic under a medium electric field of 260 kV/cm. Additionally, the ceramic also exhibits excellent temperature and frequency stability. Furthermore, the phase field simulation is used to simulate the evolution of domain structure and hysteresis loops of the ceramics with different doping levels. The results of phase field simulation explicitly explain the influence of different relaxation degrees on energy storage density and efficiency of the ceramics. We believe that the ceramic prepared in this work is one of the most promising candidate materials for some miniaturized energy storage devices operating under low or medium electric fields. [ABSTRACT FROM AUTHOR]

High-precision piezo actuators necessitate dielectrics with high electrostrain performance with low hysteresis. Polarity-modulated (Sr 0.7 Bi 0.2□0.1 )TiO 3 -based ceramics exhibit extraordinarily discrete multiphase coexistence regions: (i) the relaxor phase coexistence (RPC) region with local weakly polar tetragonal ( T ) and pseudocubic (Pc) short-range polar nanodomains and (ii) the ferroelectric phase coexistence (FPC) region with T long-range domains and Pc nanodomains. The RPC composition features a specially high and pure electrostrain performance with near-zero hysteresis ( S ∼ 0.185%, Q 33 ∼ 0.038 m 4 ·C -2 ), which is double those of conventional Pb(Mg 1/3 Nb 2/3 )O 3 -based ceramics. Particular interest is paid to the RPC and FPC with multiscale characterization to unravel local structure-performance relationships. Guided by piezoelectric force microscopy, scanning transmission electron microscopy, and phase-field simulations, the RPC composition with multiphase low-angle weakly polar nanodomains shows local structural heterogeneity and contributes to a flat local free energy profile and thus to nanodomain switching and superior electrostrain performance, in contrast to the FPC composition with a macroscopic domain that shows stark hysteresis. This work provides a paradigm to design high-precision actuator materials with large electrostrain and ultralow hysteresis, extending our knowledge of multiphase coexistence species in ferroelectrics.

Dielectric capacitors possessing the inherent superiorities of high power density and ultrafast charge-discharge speed make their utilization in energy-storage devices extremely propitious, although the relatively low recoverable energy-storage density ( W rec ) may impede their applications. In this work, unlike the mainstream approach of destroying long-range ferroelectric/antiferroelectric order and inducing relaxor properties to achieve a high W rec value, we have selected end members with a high polarization gene to promote the polarization behavior of the typical relaxor Sr 0.7 Bi 0.2 TiO 3 . Therefore, an ultrahigh W rec ∼ 8 J/cm 3 and a superior efficiency (η) ∼ 91% are accomplished in the 0.98[0.56(Sr 0.7 Bi 0.2 )TiO 3 -0.44(Bi 0.5 Na 0.5 )TiO 3 ]-0.02 Bi(Mg 0.5 Ti 0.5 )O 3 sample. The achieved W rec value is record high in Sr 0.7 Bi 0.2 TiO 3 -based systems as far as we know. The polarization-enhancement behavior can be explained by the phase field simulation results, phase content variance in X-ray diffraction Rietveld refinement, hardening trend in Raman spectroscopy, domain morphology, and local symmetry in transmission electron microscope analysis. Meanwhile, the ceramic possesses excellent thermal stability (Δ W rec < 12.7% and Δη < 10.4%, -50-200 °C), frequency (Δ W rec < 2.69% and Δη < 2.06%, 0.5-500 Hz), and fatigue-resistant stability (Δ W rec < 0.08% and Δη < 0.2%, up to 1 × 10 5 cycles). Accordingly, this work proposes a design idea to tailor the polarization behavior and energy-storage properties of typical relaxors.