Papers by Keyword: Relaxor

Abstract: In this article, the structural, microstructural, and dielectric properties of Lead- free perovskite ceramic Bi_0.5(Na_0.78K_0.22)_0.5TiO₃ [BNKT] have been reported. The material was synthesized through the solid-state reaction method. The compound formed is found to have a hexagonal structure, confirmed by XRD analysis of the sample. The microstructural analysis of the compound revealed the polycrystalline nature of the ceramic having quasi-cubic grain morphology with distinct grain boundaries. From the dielectric study, it was found that the dielectric constant increases with temperature and attained maximum value at temperature T_c = 335° C, after which it decreased. The frequency independence of transition temperature (T_c) suggested the classic ferroelectric behaviour of the compound. The broad dielectric peak around transition temperature confirms the relaxor behaviour of the compound as well as diffused phase transition at T_c. The value of the relative permittivity and loss tangent at ambient temperature for 1kHz frequency is 627 and 0.223 respectively. The synthesized material can be utilized for the fabrication of capacitors and energy storage applications.

Abstract: In this study, we investigated the impact of high-energy milling on the structural and dielectric properties of Pb[Zr_(1-x)Ti_x ]O₃ [PZT] ceramics synthesized using the solid-state reaction process. The sample was milled for 2, 4 & 6 hours using a high-energy ball milling machine. The unit cell structure for all of the samples was observed to be monoclinic, according to x-ray diffraction measurements (space group: C1m1). A significant reduction in crystallite size was observed, from 132 nm to 46 nm after 6 hours of milling. The dielectric study indicated a classical ferroelectric type behaviour for the un-milled sample and diffused phase transition for all milled samples. However dielectric constant dropped from 940 to 487 after 6 hours of milling.

Abstract: This paper presents a new way of using the classical Preisach distribution to the analytical description of the behavior of ceramic ferroelectrics in a wide range of temperatures. The iteration method have been used to investigate the Preisach distribution from polarization-electric field hysteresis loops to observe the composition and temperature variation of the some parameters in lead barium zirconate titanate stannate ceramic samples. Received Preisach distributions from P-E hysteresis loops were modeled by selected analytical functions to find useful parameters to observing the evolution of the hysteresis loops with temperature. This type of analysis can allow a more complete understanding of the relaxor properties occurring in these kind of materials, and may be used to examination the changes of temperature changes of piezoelectric sensors.

Abstract: Pb (Mg_1/3Nb_2/3)O₃ (PMN) thin films were prepared by metal organic decomposition (MOD) method. The effects of Pb content and annealing temperature on the crystallinity of PMN epitaxial thin films were investigated. The 10at% Pb-excess PMN film annealed at 973 K with facing the film surface against another STO substrate have improved its crystallinity compared with those under another conditions.

Abstract: We present the technology of obtaining and the main properties of multilayered ceramic capacitors (MLCC) based on the PMN-PT-PFN solid solution. PMN-PT-PFN is the abbreviation of the material with general formula (1-y)[(1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3]-yPb(Fe1/2Nb1/2)O3. In our work the investigated material was PMN-PT-PFN with x=0.25, y=0.1 i.e. 0.9(0.75PMN-0.25PT)-0.1PFN. The powder of 0.9(0.75PMN-0.25PT)-0.1PFN has been obtained in three steps. In first step we obtained MgNb2O6. In second step FeNbO4 was obtained. In final third step the 0.9(0.75PMN-0.25PT)-0.1PFN was obtained from mixed powders MgNb2O6, FeNbO4, PbO and TiO2. Thick film pastes for obtaining MLCC were prepared by mixing of PMN-PT-PFN powder with organic vehicle and firing in furnace in the temperature range up to 1050°C. Platinum paste has been used as electrodes. The thickness of single layer was about 45 µm (including electrodes). For obtained MLCC XRD investigations were performed as well as investigations of microstructure, EDS and main dielectric properties.

Abstract: Disordered multiferroic materials (type-III multiferroics) escape the conventional schematics of type-I and type-II multiferroics, where two types of ferroic long-range order are expected to coexist under different interdependences and promise to attain a maximized bilinear (α or EH) magnetoelectric effect under special symmetry conditions. Nevertheless sizable higher order ME response occurs also in disordered systems such as in the simultaneous dipolar and spin glasses (multiglass) Sr_0.98Mn_0.02TiO₃ and K_0.94Mn_0.03TaO₃, the quantum paraelectric antiferromagnet EuTiO₃, the spin glass and relaxor ferroelectric PbFe_0.5Nb_0.5O₃, and the antiferroelectric antiferromagnetic dipole glass CuCr_1-xIn_xP₂S₆. They have in common to show large quadratic magneto-capacitance effects, Δε H², which are related to dominating third-order E²H² terms in their free energies and do not require special symmetry conditions. The polarization controlled exchange coupling can achieve giant fluctuation-enhanced values in the vicinity of critical magnetic fields as observed, e.g., in EuTiO₃. Exceptionally, even the first-order EH-type magnetoelectric effect is observed whenever metastable homogeneous order parameters are induced by field cooling as in EuTiO₃, or in the spin glass phase of the relaxor multiferroic Pb (Fe_0.5Nb_0.5)O₃ at T < T_g = 10.6 K.

Abstract: Perovskite-based (1-x) (Na_0.5Bi_0.5)TiO₃-x NaNbO₃ [(1-x) NBT-x NN, x = 0.1, 0.2, 0.3 and 0.4] ceramics were sintered at 1080°C. Dielectric characteristics, crystalline structures, and Raman investigations were carried out on (1-x) (Na_0.5Bi_0.5)TiO₃-x NaNbO₃ ceramics. X-ray diffraction (XRD) patterns showed that NaNbO₃ ceramic would form a solid solution with (Na_0.5Bi_0.5)TiO₃ ceramic, and and unknown or second phases were not observable as well. NaNbO₃ ceramic diffused into the crystalline structure of (Na_0.5Bi_0.5)TiO₃ ceramic and (1-x) NBT_-x NN ceramics still revealed a rhombohedral structure. The temperature-dielectric constant curves showed that as NN content increased, the temperature to reveal the maximum dielectric constant (T_m) was raised, the depolarization temperature (T_d) was shifted to lower value, and the dielectric constant at Tm and the loss tangent at T_d gradually decreased. The Raman bands at 770 and 830 cm^-1 were attributed to the existence of the oxygen vacancies. In this study, the relaxor-type ferroelectric properties of NBT ceramic had been improved as NN ceramic was added.

Abstract: Relaxor characteristics of (1-x)BaTiO₃-xBi(Mg_1/2Ti_1/2)O₃ (x=0.1–0.7) ceramics were investigated. Microstructural observation showed second phases and no domain structure for the sample with x=0.6. Deviation from the Curie-Weiss behavior was found in temperature dependence of the inverse permittivity for all the samples. The stronger dielectric dispersion was found for x=0.6 and 0.7 and they were described by the Vogel-Fulcher relationship. The temperature dependence of the remanent polarization and coercive field indicated the freezing temperature was 100~150°C for x=0.6. The strong dielectric dispersion of x=0.6 is believed to be induced by the structural disorder due to the second phases.

Abstract: We researched the phenomenon that the permittivity of dielectric layers in multilayer ceramic capacitor (MLCC) increases with the number of dielectric layers. Finite element method (FEM) shows that the internal residual stress in MLCC was generated by the difference of thermal expansion coefficient between internal electrodes and dielectric layers. We developed a electric measurement system with applying external stress for understanding the stress influence on dielectric properties. The compressive stress along electric field increased the polarization. The polar nano regions (PNRs) in shell composition dielectrics were easily influenced by stress. Based on these results, the relationship between the number of dielectric layers and their permittivity in MLCCs was explained.

Abstract: Lead zinc niobate (PZN) added lead zirconate titanate (PZT) thick films with thickness of 5~10 μm were fabricated on silicon and sapphire substrates using aerosol deposition method. The contents of PZN were varied from 0, 20 and 40 %. The as deposited film had fairly dense microstructure without any crack, and showed only a perovskite single phase formed with nano-sized grains. The as-deposited films on silicon were annealed at temperatures of 700oC, and the films deposited on sapphire were annealed at 900oC in the electrical furnace. The effects of PZN addition on the microstructural evolution were observed using FE-SEM and HR-TEM, and dielectric and ferroelectric properties of the films were characterized using impedance analyzer and Sawyer-Tower circuit, respectively. The PZN added PZT film showed poor electrical properties than pure PZT film when the films were coated on silicon substrate and annealed at 700oC, on the other hand, the PZN added PZT film showed higher remanent polarization and dielectric constant values then pure PZT film when the films were coated on sapphire and annealed at 900oC. The ferroelectric and dielectric characteristics of 20% PZN added PZT films annealed at 900oC were comparable with the values obtained from bulk ceramic specimen with same composition sintered at 1200oC.