Search

High-performance colossal permittivity (ε′ > 104) plays an indispensable role in the development of electronic field. In this work, ultra-high dielectric permittivity (ε′ > 237, 294 @1 kHz) and low dielectric loss (0.012 @1 kHz) were simultaneously achieved in Ta-doped BaTi0.995Ta0.005O3 ceramics. Importantly, the dielectric permittivity changes less than 15% between − 55 and 200 °C, and the dielectric loss is less than 0.04. The excellent giant dielectric performance is related to the defect dipoles of electronic pins associated with electrons/oxygen vacancies/Ti3+, which are generated by B-site donor. And the thermal-activated short-range hopping of electrons is conformed to be the origin of low dielectric losses and excellent thermal stability. This work provides a strategy for achieving ultra-high dielectric permittivity, low dielectric loss, and excellent temperature stability of Ta-doped BaTiO3 simultaneously through B-site defect engineering. [ABSTRACT FROM AUTHOR]

A series of low-permittivity LiAl1 − xBxO2 (0.01 ≤ x ≤ 0.10) ceramics were fabricated by a conventional solid-state reaction method and were characterized for their phase evolution, crystal structure, and dielectric properties. Single-phase LiAl1 − xBxO2 solid solutions were formed at a limited compositional range (x = 0.05) while the secondary phase Li2(BAlO4) companied at higher dopant contents. Boron substitution facilitated the sintering behavior and optimized the densification of LiAlO2, resulting in dense microstructures and improved dielectric properties. A composition with x = 0.075 exhibited a high quality factor (Q×f) of 40,288 GHz along with a low relative permittivity (εr) of 6.3 and a temperature coefficient of resonance frequency (τf) of – 191 ppm/oC. All results indicate that the LiAl1 − xBxO2 ceramics can be a promising candidate material in the application of the substrate. [ABSTRACT FROM AUTHOR]

The tungsten bronze ceramics were prepared by solid-state reaction method to investigate the effect of La3+ concentration on the microstructure, dielectric and ferroelectric properties of Sr4 − xNa2 − xLaxTa0.6Nb9.4O30 (SNLTN: 0 ≤ x ≤ 0.4). X-ray diffraction results show that the tungsten bronze phase structure was a tetragonal phase in the P4bm space group at room temperature. The A-site structural vacancies increases as the structure transformed from “filled” to “unfilled” state. At the same time, the distortion of the BO6 octahedral increases. The results of the temperature dependence of the dielectric constant indicate that adding La3+ promotes the emergence of dipole-glass-like behavior and enhances dielectric relaxation. To better understand how polar clusters in Sr4 − xNa2 − xLaxTa0.6Nb9.4O30 ceramics change with increasing x, the size and kinetic behavior of PNRs were calculated and analyzed using the Vogel-Fulcher relationship and macroscopic and phenomenological statistical model, which reveals that the thermal stability of the dielectric constant is inversely related to the size of PNRs in addition to the long-range ordering of the system is disrupted. Hence, it is critical for the energy storage performance to obtain small size and the high number of active PNRs and the weak coupling between PNRs and other polar clusters. Finally, an energy storage density of 2.06 J/cm3 was received in Sr3.8Na1.8La0.2Ta0.6Nb9.4O30. [ABSTRACT FROM AUTHOR]

Compositional modification engineering was designed to simultaneously reduce the sintering temperature and improve the dielectric properties of BaTa2V2O11 via in-situ adjusting the V5+/Ta5+ molar ratio. A series of BaTa2-xV2+xO11 ceramics, fabricated by a solid-state reaction method, were characterized for structural evolution and dielectric properties variations. In-situ adjusting V5+/Ta5+ molar ratio significantly lowered the sintering temperature of BaTa2V2O11 and prominently improved the temperature stability of resonance frequency which is explained by the dielectric dilution theory. Competitive microwave dielectric properties with εr = 11.5–25.9, Q × f = 22,172–42,660 GHz, and τf = 42.4–74.6 ppm/ºC were achieved in the BaTa2-xV2+xO11 ceramics sintered at 620–840 oC. All the results indicate that the molar ratio of V5+ is primarily responsible for improving the densification behavior and dielectric characteristics of BaTa2-xV2+xO11, which in turn increases the appropriateness in further practical applications. [ABSTRACT FROM AUTHOR]

In this study, Ba4RCo0.5Nb9.5O30 (R = La, Nd, Sm, Eu) (BRCN) ceramics were synthesized using a high-temperature solid-state reaction. The XRD refinement results show that ceramic samples are tetragonal tungsten bronze (TTB). As the radius of rare-earth ions decreases, the unit cell volume of BRCN ceramics decreases, and the radius difference between Ba2+ and R ions increase, which results in BO6 octahedral distortion and the Raman peaks shift to high frequency. In addition, as the radius of rare-earth ions decreases, the ionic displacements increase and thus the dielectric constant peak temperature goes up. The high-temperature impedance results show that there exists n-type electronic conduction in the samples. The remanent polarization of the P–E curve at low frequencies increases from 0.470 to 1.038 μC cm−2 as the rare-earth ion radius decreases. [ABSTRACT FROM AUTHOR]

The electric properties affected by the applying magnetic field or vice versa are known as magnetoelectric effect (ME effect), which caused great concern in recent years. Here, we reported the electric, magnetic and magnetoelectric properties of polycrystalline Y-type hexaferrite BaSrCo2Fe11.5Ga0.5O22. In particular, the frequency and temperature dependence of impedance, electric modulus, and ac conductivity, were studied. Grain and grain boundary effects were coexistent at low temperature of this sample, while at high temperature grain boundary effect was dominated. In addition, the universal power law (UPL) and superlinear power law (SLPL) regions were coexistent at low temperature. The magnetic transition temperature from helimagnetism to ferromagnetism was found at around 200 K. The magnetoelectric (ME) effect has been detected in the sample, and the ferroelectric polarization is induced by the magnetic field. What is more, the polarization can be reversed as the magnetic field changes signs. These results show that this ferrite is a good candidate for high temperature multiferroic applications and is also a good prototype for studying the SLPL mechanism in inorganic materials. [ABSTRACT FROM AUTHOR]

Unfilled tungsten bronze ceramics with general formula KBaRNbO (R = La, Pr, Nd, Sm, Eu, Gd) were prepared by the conventional solid state reaction method. XRD patterns show that all ceramics are pure tungsten bronze phase. Dielectric characterization indicates that the ceramics except KBaGdNbO are relaxors with strong frequency dispersion, while KBaGdNbO shows diffuse phase transition and belongs to classical ferroelectrics. At room temperature, the KBaRNbO compounds (R = La, Pr, Nd) are paraelectrics while the KBaRNbO compounds (R = Sm, Eu, Gd) are ferroelectrics. Among them, KBaGdNbO has the highest remnant polarization (2 P) of 8.2 μC/cm. Phase transition temperature, remnant polarization (2 P) and tetragonality of the compounds increase with the decrease of ionic radius of the rare earths. [ABSTRACT FROM AUTHOR]

Giant dielectric ceramics CaCuTiO (CCTO) with non-ohmic electrical properties were prepared by a sol-gel processing method. Crystal structure and microstructure of the ceramics have been characterized using X-ray diffraction and Scanning electron microscopy. The effects of sintering duration and cooling rate on electrical properties of the ceramics were investigated by measuring the properties of permittivity, I- V and grain-boundary barriers. Prolonging holding time led to substantial improvement in permittivity, furthermore, the quenched sample showed larger dielectric permittivity than the furnace-cooling one. The non-ohmic behavior relating current density ( J) to the applied electric field ( E) at different temperatures was characterized. A low-voltage and giant dielectric permittivity CCTO varistor with breakdown voltages in the range of E = 0.2-3 kV cm, nonlinearity coefficient α = 2-6 and dielectric permittivity ε = 4,000-30,000 was obtained. A linear relationship between ln( J) and E indicated that a Schottky barrier should exist at the grain boundary. [ABSTRACT FROM AUTHOR]

(1 − x)(KNa)NbO-xSrBaNbO [(1 − x)KNN-xSBN] ceramics were synthesized by solid-state reaction technique. X-ray diffraction analysis of samples indicated that a single orthorhombic perovskite phase was formed as the x value is ≤0.02. Optimized piezoelectric properties with d = 126 pC/N, K = 0.39, Q = 201 were obtained for 0.98KNN-0.02SBN ceramic. The dielectric properties studies illustrated that both peaks of orthorhombic to tetragonal ( T) and ferroelectric tetragonal to paraelectric cubic ( T) phase transition shifted to lower temperature. The maximum remanent polarization ( P = 22.5 μC/cm) for 0.98KNN-0.02SBN was obtained by the polarization versus electric field ( P- E) researches. AC conductivity of samples increased with increasing the temperature. The calculated activation energy of the dc conductivity was 0.9654 eV, which may be due to thermal activation. [ABSTRACT FROM AUTHOR]