Journal of Advanced Dielectrics

High performance dielectric capacitors are ubiquitous components in the modern electronics industry, owing to the highest power density, fastest charge–discharge rates, and long lifetime. However, the wide application of dielectric capacitors is limited owing to the low energy density. Over the past decades, multiscale structures of dielectric ceramics have been extensively explored and many exciting developments have been achieved. Despite the rapid development of energy storage properties, the atomic structure of dielectric materials is rarely investigated. In this paper, we present a brief overview of how scanning transmission electron microscopy (STEM) is used as a tool to elucidate the morphology, local structure heterogeneity, atomic resolution structure phase evolution and the correlation with energy storage properties, which provides a powerful tool for rational design and synergistic optimization.

This paper focuses on the problems encountered in the production process of electronic-grade polycrystalline silicon. It points out that the characterization of electronic-grade polycrystalline silicon is mainly concentrated at the macroscopic scale, with relatively less research at the mesoscopic and microscopic scales. Therefore, we utilize the method of physical polishing to obtain polysilicon characterization samples and then the paper utilizes metallographic microscopy, scanning electron microscopy-electron backscatter diffraction technology, and aberration-corrected transmission electron microscopy technology to observe and characterize the interface region between silicon core and matrix in the deposition process of electronic-grade polycrystalline silicon, providing a full-scale characterization of the interface morphology, grain structure, and orientation distribution from macro to micro. Finally, the paper illustrates the current uncertainties regarding polycrystalline silicon.

Large-size electronic-grade polycrystalline silicon is an important material in the semiconductor industry with broad application prospects. However, electronic-grade polycrystalline silicon has extremely high requirements for production technology and currently faces challenges such as carbon impurity breakdown, microstructure and composition nonuniformity and a lack of methods for preparing large-size mirror-like polycrystalline silicon samples. This paper innovatively uses physical methods such as wire cutting, mechanical grinding and ion thinning polishing to prepare large-size polycrystalline silicon samples that are clean, smooth, free from wear and have clear crystal defects. The material was characterized at both macroscopic and microscopic levels using metallographic microscopy, scanning electron microscopy (SEM) with backscattered electron diffraction (EBSD) techniques and scanning transmission electron microscopy (STEM). The crystal structure changes from single crystal silicon core to the surface of the bulk in the large-size polycrystalline silicon samples were revealed, providing a technical basis for optimizing and improving production processes.

Developing environmental-friendly materials with high-density energy storage is of paramount importance to meet the burgeoning demands for energy storage. In this study, we harness the modulation of a multicomponent solid solution by introducing KNN as a third element into the BNT–BST system, thereby achieving a marked enhancement in both energy storage performance and the temperature stability of the dielectric constant. BNBST–4KNN stands out for its exceptional dielectric stability, with a dielectric constant variation rate within 10% across a broad temperature range of $40^{\circ }$C to $400^{\circ }$C, a feat attributed to the flattening and broadening of the $T_m$ peak. BNBT–2KNN exhibits superior energy storage capabilities, with an energy storage density of 1.324 J/cm³ and an energy storage efficiency of 72.3%, a result of the P–E loop becoming more slender. These advancements are pivotal for the sustainable progression of energy storage technologies.

In this study, BNBT-KNN-xTa₂O₅ was designed and synthesized, successfully achieving a reduction in the relaxor-ferroelectric phase transition temperature. Synergy between temperature-dependent ferroelectric testing and dielectric spectroscopy confirmed that the depoling temperature gradually decreased with increasing doping concentration. Fitting of the relaxation parameter and freezing temperature substantiated that the incorporation of Ta₂O₅ increased the degree of relaxation in BNBT-KNN-xTa₂O₅, thereby effectively lowering the relaxor-ferroelectric phase transition temperature.

This paper delves into the analysis of shear wave propagation with a sandwiched structure comprising a piezoelectric layer and an elastic layer, with a transversely isotropic layer in between. The frequency equation has been derived following Biot’s theory. The dimensionless phase velocities numerical values are computed and visually depicted to demonstrate their dependencies on anisotropy, piezoelectricity, initial stress and porosity in a comparative manner. The explicit demonstration of the relationship between each parameter and the geometry has been presented. The observation shows that as porosity in the medium increases, the phase velocity also increases. Furthermore, the existence of medium anisotropy results in a decrease in the phase velocity of shear waves. Moreover, a correlation is observed where higher tensile initial stress within the medium leads to a corresponding reduction in the phase velocity of shear waves. We conclude that considered parameters (viz. piezoelectricity, anisotropy, porosity, initial stress and thickness of layers) affect the velocity profile of the shear waves significantly. This study holds practical significance in the development of innovative-layered composites, surface acoustic wave (SAW) devices and sensors utilizing intelligent piezoelectric devices for engineering purposes.

Interfacial engineering is important for ferroelectric thin-film heterostructures because of the modulation of boundary conditions of the spontaneous polarizations and their switching behaviors, which are essential for ferroelectric electronics. In this work, we study the effects of interfacial buffering layer, 5-nm-thick SrTiO₃ (STO), on the imprint and domain switching of epitaxial Pt/Pb(Zr,Ti)O₃/SrRuO₃ (SRO) thin-film heterostructures and capacitors. By buffering the ultrathin SrTiO₃ layer at the Pb(Zr,Ti)O₃ surface, the imprint effect can be dramatically alleviated as observed in the piezoresponse force microscopy (PFM)-measured domain structures and polarization–electric field hysteresis loops in thin-film capacitors. However, when the SrTiO₃ layer is buffered at the Pb(Zr,Ti)O₃/SrRuO₃ interface, the imprint effect is slightly increased. These phenomena are explained based on the band alignments among the Pt and SrRuO₃ electrodes and the Pb(Zr,Ti)O₃ layer associated with the existence of oxygen vacancies in the SrTiO₃ layer. With the reduction of imprint effect, the domain switching dynamics are also improved in the SrTiO₃-buffered Pb(Zr,Ti)O₃ capacitor, in which the switching activation field is decreased by about 45.3% in comparison with that of the pristine capacitor. These results facilitate the design and optimization of ferroelectric devices with the improvements in domain configurations, switching behaviors and band alignments.

The development of multifunctional materials with optical and electrical properties has become a research hotspot in recent years. In this work, multifunctional 0.935(Bi${}_{0.5}$Na${}_{0.5}$)TiO₃–0.065BaTiO₃ (BNT–BT)-based ferroelectric ceramics doped with small amounts of CaMAlO₄ ($\mathrm{\text{M}}=\mathrm{\text{Dy}}$, Ho) were prepared, and the effect of CaMAlO₄ on the electrostrain and photoluminescence properties of the ceramics was studied. The results showed that the CaMAlO₄ addition weakened the ferroelectric properties of the BNT–BT matrix, and promoted the improvement of the electrostrain performance. For samples doped with 1.5mol% CaMAlO₄, the unipolar strain $S_{\mathrm{\text{uni}}}$ reached the largest values, which were 0.33% ($\mathrm{\text{M}}=\mathrm{\text{Dy}}$) and 0.38% ($\mathrm{\text{M}}=\mathrm{\text{Ho}}$) under an electric field of 70kV/cm, corresponding to a large signal $d_{33}^{\ast }$ ($S_{max}∕E_{max}$) of 471pm/V ($\mathrm{\text{M}}=\mathrm{\text{Dy}}$) and 543pm/V ($\mathrm{\text{M}}=\mathrm{\text{Ho}}$), respectively. In addition, due to the existing Dy${}^{3+}$ and Ho${}^{3+}$ luminescent ions, the modified samples exhibited excellent photoluminescence performance, which exhibited bright yellow emission ($\mathrm{\text{M}}=\mathrm{\text{Dy}}$) and green emission $(\mathrm{\text{M }}=\mathrm{\text{Ho}})$ under the blue excitation. Due to their multifunctional features, these materials have potential applications as “on-off” actuators, optical-electro integration and coupling devices.