Journal of Advanced Dielectrics

In this paper, silver (Ag) nanoparticle-modified zinc oxide (ZnO) nanowall photoconductive ultraviolet photodetector was prepared by using magnetron sputtering technology, electron beam evaporation method and hydrothermal method. The results showed that ZnO nanowalls exhibited a hexagonal wurtzite structure. ZnO nanowalls grew uniformly perpendicular to the substrate, and metallic Ag nanoparticles were uniformly attached to the surface of ZnO nanowalls, effectively improving the ZnO nanowall absorption capability in the ultraviolet light region. The dark current of the Ag-modified ZnO nanowall UV detector deposited by sputtering for 40s was 0.042mA, revealing a decrease of 44%. Under the irradiation of ultraviolet light with a wavelength of 325nm, the photocurrent reached 3.088mA, which increased by four times. The responsivity increased from 27.29 to 101.07mA/W, and the sensitivity increased from 8.07 to 73.52. In addition to the good repeatability and stability, the response time was reduced by 64%, and the recovery time was decreased by 50%.

An analysis of heterophase states was carried out for ferro-active solid solutions of the system ($1-x-y$)NaNbO${}_3-x$KNbO${}_3-y$CdNb₂O₆. A complete stress relief at interfaces between phases in solid solutions with $y=0.05$ and $x=0.10$, 0.40, and 0.45 is realized at the single-domain state of the tetragonal and orthorhombic phases. In solid solutions with $y=0.05$ and $x=0.05$ and 0.20, as well as with $y=0.075$ and 0.10, and $x=0.15$, the formation of a planar interphase boundary being parallel to a zero-net-strain plane occurs at the elastic matching of the single-domain tetragonal and polydomain orthorhombic phases. In contrast to this, at $y=0.05$ and $x=0.25$, 0.30, and 0.35, the complete stress relief is associated with a co-existence of the single-domain orthorhombic and polydomain tetragonal phases, however in some cases, the tetragonal phase aims at a monodomainization.

0.7Bi${}_{(1-x)}$Nd_xFeO₃–0.3BaTiO₃ (BNFO–BTO, $x=0.005$, 0.010, 0.020 and 0.050) ceramics were fabricated using the high-temperature solid-state reaction method. The X-ray diffraction (XRD) patterns revealed that the primary phase in these ceramics was pseudocubic. The Scanning Electron Microscopy (SEM) micrographs exhibited dense microstructures throughout all BNFO–BTO ceramics. Furthermore, the temperature dependence of dielectric behaviors and ferroelectric hysteresis loop shapes suggested the occurrence of a relaxor ferroelectric-type phase transition in BNFO–BTO ceramics. Additionally, the frequency dispersion characteristics and remnant polarization were enhanced with increasing substitution of Bi${}^{3+}$ by Nd${}^{3+}$. Conducted impedance analysis on 0.7Bi${}_{(1-x)}$Nd_xFeO₃–0.3BaTiO₃ ceramics and two dielectric responses of the grain at high frequency and grain boundary at low frequency were illustrated, respectively. The combination of imaginary impedance ($Z^{″})$ and imaginary modulus ($M^{″})$ versus logf plots revealed that the charge carriers’ motion was not entirely long-range, short-range migration also exists. Through calculations based on Curie–Weiss Law, the relaxation activation energy ($E_a)$ and conductance activation energy ($E_c)$ were investigated, confirming that doping Nd${}^{3+}$ effectively mitigates the concentration of oxygen vacancies (OVs) and prevents the formation of oxygen vacancies clusters, ultimately suppressing conductivity in BNFO–BTO ceramics.

In this paper, based on the developed statistical-thermodynamic model, which is based on data on the local structure of the compound and taking into account the striction interaction caused by the large sizes of the Ba and K cations, the formation of ferroelectric phases in BaTiO₃ and KNbO₃ perovskites has been studied. Based on the modified eight-minimum model, it has been possible to qualitatively identify the factors that determine the features of the thermodynamic behavior of these crystals and to reproduce the process of formation of the whole set of phase states observed in BaTiO₃ and KNbO₃.

Electronic and dielectric properties are essential for understanding many functional materials, predicting their behavior and optimizing their performance across different shapes, geometries and scales. Several approaches were developed and explored to investigate more or less deeply the appropriate properties. One of the most appealing, accurate and efficient approach is first principle simulations based on modern theory of polarization. Especially with the increased availability of powerful computational resources and techniques. Building upon these advancements, our contribution aims to elucidate an efficient methodology for studying electronic and dielectric properties by applying the Berry phase and Maximally Localized Wannier functions methods. Our exploration will initially focus on a systematic study of the electronic, chemical bonding, ferroelectric and piezoelectric properties of the well-known prototypical bulk system PbTiO₃. Subsequently, we will extend our study to examine slab properties as surface termination and slab thickness effect on electronic properties, utilizing the robust Wannier-justified Tight Binding model.

Yttrium oxide–magnesium oxide (Y₂O₃–MgO) composite nanopowders were synthesized via three distinct methods: sol–gel, co-precipitation and glycine–nitrate process. The synthesized powders were calcined at various temperatures, and their microstructure, specific surface area and particle size were characterized. A comparative study was conducted to assess the impact of the synthesis method on the microstructure and transparency of the resulting ceramic sintering. Notably, the powder synthesized by the sol–gel technique exhibited the highest specific surface area and superior light transmittance, reaching a maximum of 85.33% at a wavelength of 5.31$\mu$m.

In this paper, we present the study of the shape change on the polar surface and in the bulk of the walls of lamellar domains as a result of local switching by focused ion beam. Periodical lamellar domain structures (PDS) are created alternatively by two methods: (i) electric-field poling using photolithographically defined electrodes and (ii) ion beam poling. The dot irradiation of Z${}^{+}$ areas near the walls of lamellar domains leads to the formation of faceted or rounded hexagonal domains. For e-field PDS additional formation of nanodomain ensembles was observed. We have revealed two types of domain wall shape changes induced by irradiation: (1) merging of the hexagonal domain with the domain wall for Z${}^{+}$ areas; (2) formation of rounded distortion of the domain wall for Z⁻ areas. For Z${}^{+}$ areas irradiation, the domain wall distortion was described by a simple model of independent growth of isolated domain with its subsequent merging with a static domain wall. For Z⁻ surface irradiation, the domain wall shift increases linearly with the distance between the irradiation dot and the wall. It was revealed that the merging between the growing hexagonal pyramid domain and lamellar domain can be obtained in the bulk even for absence of merging at the surface. All obtained results have been explained within a kinetic approach to the domain wall motion by step generation. The switching field consists of inputs produced by: (i) the charges injected during dot irradiation into the photoresist layer and crystal bulk, (ii) the charges injected during the creation of i-beam PDS, (iii) the depolarization fields. The transition of the shapes of isolated domains and wall distortions from faceted to rounded ones with field increase was attributed to the transition from determined step generation to stochastic one.

This paper presents the results of an experimental study of the percolation behavior of the complex dielectric constant of ceramic matrix composites (CMC). Samples of piezoactive CMC were obtained by joint sintering of synthesized PZT piezoceramic powder (matrix) and crushed particles of sintered PZT piezoceramics (filler) of different compositions. The experimental dependencies of real and imaginary parts of the complex dielectric constant of CMC on the porosity of piezoceramic matrix and volume content of ceramic filler particles were measured and analyzed. It was shown that the additional porosity of the ceramic matrix resulting from sintering of the CMC masks the dielectric percolation transition, that actually occurs at the volume concentration of ceramic filler close to percolation threshold (V ∼ 1/3).

In this work, a series of BiFeO₃/ZnO composites with varying molar ratio of BiFeO₃ to ZnO (Bi:Zn = 2.5:1, 5:1, 10:1, 20:1) have been synthesized via a one-step hydrothermal method and evaluated for their efficiency in rhodamine B (RhB) degradation performance. The morphology results reveal that the microsphere-shaped ZnO is dispersed on the surface of the blocky-like BiFeO₃, with intimate contact between the two phases. It has been found that the maximum piezocatalytic activity could be achieved at BiFeO₃/ZnO molar ratio of 5:1, with a degradation rate up to 92% for RhB. Compared with pure BiFeO₃ and ZnO, the composites have superior piezocatalytic degradation performance. The reason for the enhanced piezocatalytic dye degradation rate may be that the BiFeO₃/ZnO composites effectively separate the positive and negative charges to reduce the recombination of positive and negative charges. These active species, such as superoxide radicals (${\text{O}}_2•-$) in the process of piezocatalytic, are proved on the active species capture experiments. The BiFeO₃/ZnO composites have good piezocatalytic degradation performance, which provides an option for collecting vibration energy to degradation dye wastewater in the future.

Dielectrics with high permittivity and temperature stability are important for the development of high-temperature multilayer ceramic capacitors (MLCCs). In this study, Ca${}_{1-x}$Na_xTi${}_{1-x}$Nb_xSiO₅ (abbreviated as CTS$-x$NN) ceramics were prepared by solid-phase reaction method. The introduction of NN weakens the long-range ordered displacement of Ti, leading to a significant increase in the dielectric temperature stability. The CTS−2%NN samples exhibit high permittivity (53) and TCC $\le \pm 170$ ppm/^∘C in the range of $-55^{\circ }$C to 300^∘C. The CTS-based ceramics behave high dielectric temperature stability. In addition, the bandgap of the CTS-based ceramics increased significantly, which is favorable for improving the breakdown strength of the material. For $x=4$% samples, the breakdown strength reaches 621kV/cm. Thus, the designed CTS-based dielectrics are promising for high-temperature capacitors.