Relaxor Dielectric Properties Research Articles

Enhanced dielectric energy storage performance of Na0.5Bi0.5TiO3-LiTaO3-based lead-free relaxor ferroelectric ceramics through domain structural regulation and improved densification

Ceramic materials with relaxor dielectric properties, expressed as (1-x)(0.94Na0.5Bi0.5TiO3-0.06LiTaO3)-xCaTiO3 [(1-x)(NBT-LT)-xCT] with x values of 0.12, 0.15, 0.18, and 0.21, were synthesized through an A-site doping method to enhance energy storage capabilities. The linear dielectric CaTiO3 was chosen as the acceptor additive, and ceramic samples were prepared using conventional solid-phase and molding techniques. A comprehensive investigation evaluated the influence of different CT concentrations on the phase and energy storage/release characteristics of NBT-LT.Optimal performance was notably achieved with a 15% CT doping concentration, resulting in Wrec and η values of 2.16 J/cm³ and 70%, respectively, for a 100 μm thick sample under a 210 kV/cm voltage. When the film was rolled to a 60 μm thickness, the voltage strength increased to 330 kV/cm, leading to enhanced Wrec (5.33 J/cm³) and η (80%). Within the temperature range of 30 °C to 150 °C, only a marginal change in Wrec (less than 10%) was observed. Frequency conversion tests across the 1 Hz to 100 Hz range demonstrated the material's relative stability, with Wrec exhibiting minimal fluctuations. These findings emphasize the outstanding temperature and frequency stability of the material. During discharge, the material displayed a power density of up to 152 MW/cm³, coupled with a discharge time of 0.3 μs, showcasing remarkable pulse discharge capabilities. The experimental results affirm the promising potential of (NBT-LT)-0.15CT lead-free relaxor ferroelectric ceramics for application in commercial capacitors.

Near-room-temperature magnetocaloric properties at 1.5 T coupled with relaxor dielectric properties in La2CoMnO6 nanoparticles

Achieving high magnetic entropy change at low magnetic fields near room temperature may pave the way to attaining room temperature magnetic refrigeration. We report herein on high magnetic entropy change at 1.5 T around 291 K in La2CoMnO6 manganite nanoparticles. The magnetic, magnetocaloric, and dielectric properties of La2CoMnO6 nanoparticles of sizes D = 30–40 nm are reported. Powder X-ray diffraction analysis and Raman spectra have confirmed the co-existence of a monoclinic ordered phase and a partially disordered phase. Magnetization measurements have showna long-range ferromagnetic to paramagnetic transition at a Curie temperature of 291.9 K. A maximum magnetocaloric entropy change of 0.88 J kg−1 K−1 has been achieved upon application of a 1.5 T external magnetic field. Dielectric measurements have shown relaxation behavior and a high dielectric constant. The detailed electrical conduction mechanism is explained in terms of various polaron hopping mechanisms. The mutual origin of magnetocaloric and dielectric relaxor behavior in La2CoMnO6, along with its high dielectric constant, confirms that there is strong coupling between the magnetic and dielectric properties of this material, making it suitable for multifunctional applications.

Relaxor dielectric properties of lead-free Bi4Ti3O12/Bi4.5Na0.5Ti4O15 intergrowth ceramics

Intergrowth ceramic series Bi4Ti3O12/Bi4.5Na0.5Ti4O15 have been prepared through solid state reaction. X-ray diffraction analysis shows the coexistence of Bi4Ti3O12 and Bi4.5Na0.5Ti4O15 phases with slight lattice distortion. Scanning electron micrographs present the growth of grains and grain boundaries with different contents of Bi4.5Na0.5Ti4O15. The relaxation dielectric properties of the ceramics have been observed. The room-temperature dielectric constant at 100 Hz is initially increased and then decreased with the increase of Bi4.5Na0.5Ti4O15. The impedance spectroscopy and the electrical modulus are also measured for explaining the dielectric behavior. The Nyquist plots display different semicircle arcs at 300 and 600 K. The imaginary part of electrical modulus has two peaks in the range of the measuring temperature. They prove the common influence of grains and grain boundaries on the dielectric properties. For further fitting the experimental data by Arrhenius theory, activation energy is obtained for grains and grain boundaries. Finally, the relaxor dielectric properties are attributed to the competition mechanism from the different growth situation of grains and grain boundaries with increasing Bi4.5Na0.5Ti4O15. Therefore, this kind of ceramics ought to be promising candidates for multifunctional device applications.

Stress Dependence of Dielectric Properties in Relaxor Ferroelectrics: Monte Carlo Investigation

In this work, we used Monte Carlo simulation to investigate the uniaxial stress dependence of the relaxor dielectric properties. The Metropolis algorithm and the spin glass type interaction were used in updating the local polarizations (representing the polar nano-regions). The exchange interaction in the spin glass Hamiltonian was assumed to be stress dependent via the strain. From the results, the frequency dependence of the dielectric permittivity were found, where, at high enough stress, the dielectric permittivity decreases with increasing stresses in qualitatively good agreement with experiments. In addition, from the modified Curie-Weiss law, all ’s stay close to 2. Therefore, this implies the frequency dispersion universality of the relaxor system under loading conditions.