Narrow Results

Au/n-Si metal-semiconductor (MS) and Au/Bi₄Ti₃O₁₂/n-Si metal-ferroelectric-semiconductor (MFS) structures were fabricated and admittance measurements were held between 5 kHz and 1 MHz at room temperature so that dielectric properties of these structures could be investigated. The ferroelectric interfacial layer Bi₄Ti₃O₁₂ decreased the polarization voltage by providing permanent dipoles at metal/semiconductor interface. Depending on different mechanisms, dispersion behavior was observed in dielectric constant, dielectric loss and loss tangent versus bias voltage plots of both MS and MFS structures. The real and imaginary parts of complex modulus of MFS structure take smaller values than those of MS structure, because permanent dipoles in ferroelectric layer cause a large spontaneous polarization mechanism. While the dispersion in AC conductivity versus frequency plots of MS structure was observed at high frequencies, for MFS structure it was observed at lower frequencies.

An ultra-broad working temperature dielectric material, Bi₄Ti${}_x$O${}_{12}$($x$ = 2.96, 2.98, 3.0, 3.02 and 3.04), prepared by a conventional mixed oxide route was investigated which is supposed to replace lead-containing ceramics for its outstanding dielectric properties. Microstructure and dielectric properties of well-sintered samples (at 1040${}^{\circ }$C, 1060${}^{\circ }$C, 1080${}^{\circ }$C, 1100${}^{\circ }$C and 1120${}^{\circ }$C) were studied. X-ray diffraction analysis indicated that the new material was in a single Bi-layered perovskite phase. The dielectric constant and dielectric loss at different frequencies (10, 100 and 1000 kHz) were measured at 1100${}^{\circ }$C. With the increasing frequency, the dielectric constant decreased and the dielectric loss was almost unchanged. While at 100 kHz, there is the highest relative permittivity (${𝜀}_r$) of 2822.8 and the lowest dielectric loss of 0.0040 ($x$ = 2.98), the Curie temperature ($T_c$) is 668.9${}^{\circ }$C. At the frequency of 1 MHz, the highest relative permittivity (${𝜀}_r$) is 1115.8 when Ti content is 3.02, and the Curie temperature is 672.2${}^{\circ }$C. SEM can explain the results of the dielectric spectrum at different Ti content and sintering temperatures. $Z\ast$ plots show that Bi₄Ti₃O${}_{12}$ ceramics are a kind of dielectrics. Since it possesses large dielectric constant, low dielectric loss and stable temperature character, this material shows promising applications for the ultra-broad temperature range components, such as high-temperature multilayer ceramic capacitors and microwave ceramics.

Eco-friendly, nontoxic and high-energy storage materials are very important for flexible electrode materials. Bi₄Ti₃${\text{O}}_{12}$ lead-free, perovskite phase may prove suitable as filler in composites for electrode materials because of its large spontaneous polarization. We have synthesized Bi₄Ti₃${\text{O}}_{12}$/polystyrene (BTO/PS) composites and carried out their structural, morphological and bonding studies with the help of X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR), in that order. Dielectric measurements in the broad frequency range of synthesized composites determined by Impedance analyzer. We observed that the dielectric constant of composites increased with filler concentration and decreased with applied field frequency. Bi₄Ti₃${\text{O}}_{12}$/PS composites can be good electrode materials.

Semiconductor materials used in the field of photocatalysis have been attracting much attention. Due to the advantages of green, pollution-free and sustainable development of solar energy, it is an ideal strategy to explore excellent semiconductor materials as high light photocatalysts for energy conversion. Herein, Bi₄Ti₃O${}_{12}$/CdS composites were synthetized by coprecipitation method, which CdS particles selectively deposited on Bi₄Ti₃O${}_{12}$ nanosheets. The phase structure and optical properties of the samples were characterized by XRD, SEM, N₂ adsorption–desorption and UV-visible diffuse spectra (UV-DRS). The results showed that the Bi₄Ti₃O${}_{12}$/CdS composites had the highest photocatalytic activity against RhB under visible light, and the degradation rate of RhB was 98.8% after 120min of simulated light, 2.14 times that of pure Bi₄Ti₃O${}_{12}$, and the Bi₄Ti₃O${}_{12}$/CdS-10wt.% composites also showed good stability. UV-DRS demonstrated that the optical absorption range of the composite extends to visible regions, and photocurrent tests also showed that the composite enhances the separation and migration of photoogenic electron–hole pairs, mainly due to the formation of 2D nanosheets/0D particles heterojunctions between the bronzn CdS of the perovskite BTO and hexagonal fibers. Furthermore, free radical assays confirmed that both $\cdot$O${}_2^{-}$, h${}^{+}$ and $\cdot$OH have effects in the degradation of RhB, and thus suggested a possible mechanism for the photodegradation process of the Bi₄Ti₃O${}_{12}$/CdS-10wt.% composite photocatalyst.

A kind of lead-free dielectric materials, such as the bismuth layered perovskite-type structure of Bi${}_{4–x}$Ti₃O${}_{12–1.5x}(x=0.04,0.02,0,–0.02,–0.04)$, was prepared by the conventional solid-state method at 800${}^{\circ }$C and sintered at 1100${}^{\circ }$C. The variation of structure and electrical properties with different Bi concentration was studied. All the Bi${}_{4–x}$Ti₃O${}_{12–1.5x}(x=0.04,0.02,0,–0.02,–0.04)$ samples exhibited a single structured phase. SEM could be a better approach to present the microstructure of Bi${}_{4–x}$Ti₃O${}_{12–1.5x}(x=0.04,0.02,0,–0.02,–0.04)$ ceramics. It could be found that the grain size of Bi${}_{4.02}$Ti₃O${}_{12.03}$ sintered at 1100${}^{\circ }$C was smaller than that of others among the five samples through grain size mechanics. Through impedance spectra analysis, we knew, when the Bi content was fixed, that the dielectric constant and the loss values increased with the decrease of frequency. The Curie temperature of the five samples was about 670${}^{\circ }$C. In particular, while at the frequency of 100kHz, the lowest loss was 0.001 when Bi content was 3.98. The Bi${}_{4.02}$Ti₃O${}_{12.03}$ ceramics with the minimum grain size had highest dielectric constant and the relatively low loss. Due to its high Curie temperature, high permittivity and low loss, the Bi₄Ti₃O${}_{12}$ (BIT) ceramics have a broad application prospect in high density memory, generator, sensor, ferroelectric tunnel junctions and so on.