Journal of Advanced Dielectrics

Two 0.93(Na${}_{0.5}$Bi${}_{0.5})$TiO₃–0.07BaTiO₃ ceramics were sintered for 2h and 3 h, respectively, by a conventional solid reaction method. The ceramic sintered for 2h showed a normal ferroelectric hysteresis loop and paramagnetic behavior, while the ceramic sintered for 3h showed a pinched ferroelectric hysteresis loop, weak ferromagnetism, and enhanced magnetoelectric coupling. The origins of the sintering time-related multiferroic properties are discussed in detail. The work offers a new way to induce multiferroicity in ceramics by tuning sintering time.

Piezocatalysis has emerged as a promising environmental remediation technique, and the exploration of environmentally friendly and high-performance piezocatalysts is crucial for their practical applications. In this work, the bismuth sodium titanate (Na${}_{0.5}$Bi${}_{0.5}$TiO₃ (NBT)) exhibited efficient piezocatalytic activity toward typical organic pollutants degradation, including acid orange 7, methylene blue, rhodamine B and methyl orange. Notably, rhodamine B was degraded by 98.1% within 30min with a reaction rate constant of 0.130min${}^{-1}$. Furthermore, the NBT achieved a hydrogen peroxide production efficiency of 538$\mu$mol/g⋅h without the sacrificial agent, indicating that the NBT is a superior piezocatalyst for dye degradation and hydrogen peroxide generation. This work demonstrated that by using mechanical energy, the NBT can be used for degrading organic pollutants in wastewater and hydrogen peroxide generation.

An n-type channel transparent thin film field-effect transistor (FET) using a top-gate configuration on a sapphire substrate is presented. ZnO:Li film was used as a channel, and MgF₂ film as a gate insulator. Measurements showed that ZnO:Li films are ferroelectrics with spontaneous polarization $P_S=1$–5$\mu$C/cm² and coercive field $E_C=5$–10kV/cm. The dependences of drain–source current on drain–source voltage at various gate–source voltages in two antiparallel $P_S$ states were measured and the values of field-effect mobility and threshold voltage were determined for two $P_S$ states are as follows: (a) $\mu =1.5$cm²/Vs, $U_{\mathrm{\text{th}}}=30$V; (b) $\mu =1.7$cm²/Vs, $U_{\mathrm{\text{th}}}=23$V. Thus, $P_S$ switching leads to a change in FET channel parameters. Results can be used to create a bistable or, more precisely, digital FET.

N-doped titanium dioxide (TiO${}_2)$ hollow nanospheres with abundant oxygen vacancies were successfully synthesized by coupling urea treatment and annealing in an N₂ atmosphere. The pristine TiO₂ hollow nanospheres exhibit a shallow donor level for electron trapping, while the urea treatment generates a N 2p acceptor level for hole trapping. After annealing in N₂, the sufficient N atoms generate abundant oxygen vacancies for trapping electrons, resulting in further improved charge separation efficiency. The N-doped TiO₂ exhibits the highest H₂ evolution rate, reaching 2867$\mu$molg${}^{-1}$h${}^{-1}$, which is six times higher than that of pristine TiO₂ hollow nanospheres. The introduction of oxygen vacancies by interstitial N provides a promising way to improve the photocatalysis activity of photocatalysts.

In this work, dense CdCu₃(Al${}_{1∕2}$Ta${}_{1∕2}{)}_x$Ti${}_{4-x}$O${}_{12}$ ceramics were prepared by a conventional solid phase method. The effect of Al${}^{3+}$/Ta${}^{5+}$ dopants on the dielectric properties of CdCu₃Ti₄O${}_{12}$ ceramics was systematically investigated. Upon Al${}^{3+}$/Ta${}^{5+}$ co-doping, the dielectric properties of CdCu₃(Al${}_{1∕2}$Ta${}_{1∕2}{)}_x$Ti${}_{4-x}$O${}_{12}$ were significantly enhanced. Particularly, the CdCu₃(Al${}_{1∕2}$Ta${}_{1∕2}{)}_{0.05}$Ti${}_{3.95}$O${}_{12}$ material displays a decent dielectric property, where dielectric constants (${\epsilon }_{\text{r}}\sim 27181$), loss tangent (tan $\delta \sim 0.069$) at a test frequency of 1kHz are able to satisfy the application temperature requirement of the Y6R capacitor. Surprisingly, the refined grains resulting from Al${}^{3+}$/Ta${}^{5+}$ co-doping lead to heightened resistance at grain boundaries, which is closely associated with enhanced dielectric properties. Meanwhile, the giant dielectric property of the materials can be attributed to the effect of the internal barrier layer capacitance. The obtained results are expected to provide a new idea for obtaining high dielectric constant and low loss tangent in CdCTO-based materials and promote the practical application of such materials.

Orientation anisotropy is a well-known essential character for polarization characteristics of ferroelectric materials, which has been widely investigated in conventional ferroelectric random access memories. In this work, we study the effects of orientation on the tunneling electroresistance (TER) of ferroelectric tunnel junctions (FTJs). Rhombohedral Pb(Zr${}_{0.7}$,Ti${}_{0.3}$)O₃ (PZT) that has the polar axis along the $〈111〉$ orientation is adopted as potential barriers and two kinds of FTJs that are composed of (001)- and (111)-oriented PZT barriers and Nb:SrTiO₃ (Nb:STO) electrodes, respectively, are fabricated. The (111)-oriented Pt/PZT/Nb:STO FTJ exhibits a giant ON/OFF ratio of $\sim 1.9\times 10^5$, about 30 times that of the (001)-oriented device, due to the lowered PZT barrier in the ON state and the widen Schottky barrier in the OFF state based on current and capacitance analyses. In addition, compared to the (001)-oriented device, the (111)-oriented FTJ shows a sharper and faster switching between the ON and OFF states according to the nucleation-limited-switching dynamics model, giving rise to good linearity in memristive behaviors for synaptic plasticity and reliable retention and endurance properties for the resistance switching. The improved TER properties are ascribed to larger effective polarizations and 180^∘ switching in the (111)-oriented PZT barrier. These results facilitate the design and fabrication of high-performance FTJ devices with the optimization of crystallographic orientation and polarization switching characteristics.

Dielectric relaxation behaviors of (1–x)BaTiO₃–xBi(Zn${}_{1∕2}$Zr${}_{1∕2})$O₃ (BT–BZZ, $0.04\le x\le 0.20$) have been analyzed at various temperatures. Both Havriliak–Negami (H–N) and Jurlewicz–Weron–Stanislavsky (J–W–S) relaxations are identified in these ceramic compositions. H–N relaxation happens in compositions with a small mole ratio of Bi(Zn${}_{1∕2}$Zr${}_{1∕2})$O₃ (BZZ), while J–W–S type relaxation appears in compositions with a large mole ratio. Static dielectric constant, relaxation time and Jonscher indices are also obtained. The general trend of static dielectric constants decreases with increasing mole ratio of BZZ, while the relaxation time increases dramatically correspondingly. The low Jonscher index m is about 0.45 at low temperature for compositions with high mole ratio and increases with increasing of temperature. The high Jonscher index 1–n is around 0.1 at low temperature for compositions with high mole ratio and slightly decreases with increasing of temperature. Jonscher indices diagram with compositions of different mole ratios is plotted for easy identification of the relaxation types. Our results indicate that the relaxation behaviors in this BT–BZZ system show a strong deviation from the standard Debye model.

Via the method of cold sintering with post-annealing, the lead-free ceramics ${\text{K}}_{0.45}$${\text{Na}}_{0.45}$${\text{Li}}_{0.1}$NbO₃ were prepared. The cold sintered pellet without post-annealing shows a relative density (${\rho }_r)$ of 77.9%, which is larger than ${\rho }_r$ of the green pellet via the conventional solid-state sintering (SSS) method ($\sim 65.1\%$). The cold sintered pellets were post-annealed at temperatures between $975^{\circ }$C and $1075^{\circ }$C. The effect of post-annealing temperatures on microstructure, dielectric, ferroelectric and piezoelectric properties of the ceramics was studied in detail. After being post-annealed, the relative densities and grain sizes of the ceramics were increased. The ceramics post-annealed at $1050^{\circ }$C show excellent dielectric, ferroelectric and piezoelectric properties. Compared to the conventional SSS method, the method of cold sintering with post-annealing is successful in preparing dense ${\text{K}}_{0.45}$${\text{Na}}_{0.45}$${\text{Li}}_{0.1}$NbO₃ lead-free ceramics in a wide temperature range and at relatively low temperatures.

The Curie point of barium titanate (BaTiO₃) has been a focal point of research since the discovery of its ferroelectric properties. Exploring methods to elevate the Curie point without relying on Pb as a dopant presents fresh opportunities for lead-free dielectric and/or piezoelectric materials. It is essential to avoid introducing ions like K${}^{+}$ and Na${}^{+}$, which could jeopardize the functional ceramic characteristics. This study delves into the stoichiometry of barium titanate, examining how impurities, point defects and doping techniques influence its Curie point, focus on the potential of doping and processing to enhance this property. BaTiO₃ nanopowders were synthesized directly with varying Ba:Ti ratios in an ethanol–water solution at 60^∘C, followed by sintering at 1280^∘C and characterization through dielectric spectroscopy. A comparison was made with samples doped with Si, vapor-doped with Bi and vapor-doped with Pb. Results revealed that even minimal Si doping could boost the ferroelectric properties and elevate the Curie point, while vapor-doping with trace amounts of PbO or Bi₂O₃ significantly increased the Curie point, particularly in samples with higher Ti content. The impact of vapor dopants of PbO and Bi₂O₃ was similar, with a nominal doping level of 1mol% shifting the Curie point above 140^∘C. Notably, in samples with a Ba:Ti ratio of 0.95 vapor-doped with PbO, the Curie point rose to 146^∘C, a notable increase of 16^∘C, surpassing the traditional doping efficiency. This study offers fresh insights into enhancing the Curie point of barium titanate-based materials, exploring the intricate connections among chemical stoichiometry, dopants, point defects and dielectric properties. It highlights the significant influence of chemical composition, impurities, defects and doping strategies on the dielectric characteristics of barium titanate.

X-ray diffraction and dielectric studies were performed on synthesized ceramic samples of the section (1–x) (0.8PbMg${}_{1∕3}$Nb${}_{2∕3}$O${}_3\cdot 0.2$BiScO₃)⋅ x(0.8PbTiO${}_3\cdot 0.2$BiScO₃) with $x=0$–1 of the ternary BiScO₃–PbTiO₃–PbMg${}_{1∕3}$Nb${}_{2∕3}$O₃ (BS–PT–PMN) system, including the temperature dependence of thermally stimulated depolarization currents (TSDC). It was found that the samples are solid solutions with a perovskite structure, which have cubic symmetry in the range of x = 0–0.587 and tetragonal symmetry in the range of x = 0.680–1. In the intermediate composition range of x = 0.587–0.680 (morphotropic region — MR), the samples consist of a mixture of solid solutions of different symmetries. Data on the change in dielectric properties and TSDC(T) dependencies of solid solutions with a change in their composition were obtained. It was found that samples of compositions x =0–0.625 and 0.6875–1 exhibit relaxor-ferroelectric and conventional ferroelectric properties, respectively, while samples of compositions x = 0.625–0.6875 combine ferroelectric and relaxor-ferroelectric properties.