Papers by Keyword: Ferroelectric

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: In this work, the effect of electric field on structural, photoluminescence, dielectric, and piezo/ferroelectric properties of 2.5 mole % Eu³⁺substituted sodium bismuth titanate (Na_0.5Bi_0.475Eu_0.025TiO₃ abbreviated as NBT-Eu) ferroelectric material has been investigated. Rietveld refinement on the X-ray diffraction patterns of poled and unpoled ceramics suggested lower monoclinic symmetry (Cc) with 93.64% as major phase fraction and higher orthorhombic symmetry (Pbnm) with 6.36% as minor phase fraction. For the poled composition, the monoclinic (Cc) phase fraction decreased to 83.53%, and the orthorhombic (Pbnm) phase fraction increased to 16.47%. Improved ferroelectric and piezoelectric characteristics in comparison to pure NBT were found in Eu³⁺ substituted NBT. Moreover, the substitution with Eu³⁺ enabled observation of photoluminescence (PL) emission in the visible region under an excitation wavelength of 532 nm for electrically poled and unpoled ceramics, thereby enabling additional functionality for this material along with ferroelectric and dielectric properties. Intensities of PL emissions were tuned by the application of electric poling of the ceramic, which generates the possibility of using these materials in optoelectronics device applications.

Abstract: Pb (Zr_0.35Ti_0.65)_1-xSn_xO₃ (PZST) piezoelectric ceramics with ABO₃ perovskite structure were synthesized using Solid state reaction technique. The piezoelectric, ferroelectric and dielectric behavior of PZST piezoceramics was studied systematically by varying the amount of Sn at fixed Zr/Ti ratio. It was found that sample containing Sn= 0.26 exhibit maximum piezoelectric coefficient of 324 pC/N and minimum tangent loss of 0.009. Decrease in tetragonality and Curie Temperature (Tc) was observed with the increase of Sn content. The polarization–electric field hysteresis loops for all compositions were studied and it was observed that the sample containing Sn= 0.26 exhibit maximum polarization of 0.3C/m². The synthesized PZST compositions can be utilized for Pressure sensors and maritime SONAR applications. Keywords: Piezoelectric, PZST ceramics, ferroelectric, Domains

Abstract: Magneto-electric composites of two distinct phases, ferrimagnetic-piezoelectric system with general compositional formula (x) ferromagnetic + (1-x) piezoelectric were synthesized using a hybrid technique, mechano-chemical method by sintering the mixtures of piezo-electric BaTiO3 (BTO) and ferri-magnetic Mg0.2Cu0.5Zn0.3Fe2O4 (MCZF). Here, ferri-magnetic phase component MCZF (Mg0.2Cu0.5Zn0.3Fe2O4) was prepared using auto-combustion method, whereas piezo-electric BTO was procured commercially from Sigma-Aldrich. Here, the general composition of composites is given by (x) Mg0.2Cu0.5Zn0.3Fe2O4+(1-x) BaTiO3(x=15%, 30% and 45%). Presences of two phases in these magneto-electric composites were probed using X-ray diffraction (XRD) studies. Peaks observed in the XRD spectrum indicated spinel cubic structure for MCZF ferrite and tetragonal perovskite structure for BTO and, both spinel and pervoskite structures for synthesized composites. Micro-structure of the samples has been investigated using Field Emission Scanning Electron Microscope (FESEM). Frequency dependent dielectric properties of synthesized composites were measured from 100 Hz to 1 MHz at room temperature using a precision HIOKI make LCR HI-TESTER. Dielectric dispersion was observed at lower frequencies for the synthesized composites.

Abstract: The article considers the issues of receiving nanosized Ba_0,8Sr_0,2TiO₃ ferroelectric films and diamond-like films in the range of 10‒60 GHz with various thickness between 0.1‒10 μm and their dielectric properties. Peculiarities of SHF dissipation measuring method in dielectric films are discussed. It shows the influence of structural perfection of films on the value of losses of SHF energy.

Abstract: In this research, the effects of sintering temperature on phase structure, densification, microstructure, and electrical properties of modified-BNKT ceramics were investigated. Conventional sintering of lead-free 0.97Bi_0.5(Na_0.80K_0.20)_0.5TiO₃-0.03(Ba_0.70Sr_0.30)O₃ or 0.97BNKT-0.03BSrT ceramic was investigated to clarify the optimal sintering temperature for densification and electrical properties. All ceramics were prepared by a conventional mixed oxide and sintered at various temperatures from 1100 to 1150°C. XRD pattern indicated all ceramics exhibited a single perovskite without any secondary phases. The maximum density of 5.80 g/cm³ with relative density of 99.32% were observed for the ceramic sintered at 1125°C. Grain size tended to increase with increasing the sintering temperature. The good dielectric (T_d = 121 °C, T_m = 320 °C and e^¢_max = 4982) and ferroelectric properties (P_r = 16.66 µC/cm², E_c = 17.85 kV/cm and R_sq = 0.74) were obtained for the ceramic sintered at optimum sintering temperature of 1125°C.

Abstract: In this paper, we study the electrical properties and breakdown phenomena of BaTiO₃/Teflon composite ferroelectric thin film in electrowetting systems. The experimental results showed that the electrowetting effect and the breakdown voltage depend on DC voltage polarity, and this polarity dependence is closely related to the thickness of the ferroelectric film. Under AC voltages, the breakdown voltage increased directly with voltage frequency. These results are useful for designing reliable EWOD devices with low operation voltages and high robustness.

Abstract: We present a simple and cost effective method for the design and fabrication of electrowetting devices using a nanocomposite thin film of BaTiO₃ and Teflon-AF as the dielectric layer to achieve low voltage operation. The nanocomposite film is prepared by using Teflon-AF as matrix and BaTiO₃ nanoparticles as the filler material. The solution is spin coated to deposit thin film on metal electrodes. The characterization results show that the nanocomposite thin film can serve as the dielectric for EWOD with a high dielectric constant and a crack free hydrophobic film. To test the electrowetting effect, the variation of droplet contact angle achieved with DC voltage, AC voltage and AC frequency change are fully experimented. The EWOD device with nanocomposite dielectric layer also manipulates water droplet at low driving voltages. This study shows the potential of using ferroelectric nanocomposite film as the dielectric layer in high-performance EWOD devices.

Abstract: Magnetoelectric (1−x) BNT−x CFO nanoparticulate thin films with (x = 0, 0.1, 0.2, 0.3) were fabricated by a chemical solution deposition technique. The X-ray diffraction shows that no other secondary phases are observed. Transmission electron microscope (TEM) revels that CFO nanoparticles were well distributed in matrix of BNT. The nanocomposite films exhibit both good magnetic and ferroelectric properties at room temperature (R-T), as well as enhanced magnetoelectric coupling. The composite with x = 0.2, showed the large value of ME voltage coefficient (α_E ) ~ 163 mV/cmOe. These ME composites provide a great opportunity as potential lead free systems for ME devices.