Papers by Keyword: Dielectric

Abstract: The present study discusses the fabrication of non-lead ceramic/polymer composites employing (Na_1/2Bi_1/2)TiO₃ (NBT) ceramic powder as a filler and poly(vinylidene fluoride); PVDF as a polymer matrix. The NBT (volume fraction, ϕ = 1) ceramics were synthesized using the conventional mixed-oxide method followed by the high-energy ball milling method whereas (1-ϕ)PVDF/ϕ(Na_1/2Bi_1/2)TiO₃; 0 ≤ ϕ ≤ 0.3 composites were prepared from a melt-mixing process. It was observed that the real and imaginary parts of dielectric permittivity, ac conductivity, and longitudinal piezoelectric charge coefficient increase with the increase in NBT-content. Different dielectric mixing models were presented to determine the effective complex permittivity of the composites. Five dielectric mixture equations have been chosen to test the acceptability of experimental data. It was revealed that theoretical models as given by Bruggman, Rother-Lichtenecker, and modified Rother-Lichtenecker show good agreement with the experimental results of filler-concentration dependent alteration of effective relative permittivity and loss factor of the PVDF/NBT composite. A mathematical model of first-order exponential growth has also been proposed, which fitted excellently the experimental data (r² > 0.998).

Abstract: The structure, microstructure, Fourier transformed infrared spectra, dielectric, and impact generated energy harvesting characteristics of x(Ba_0.7Ca_0.3)TiO₃–(1-x)Ba (Zr_0.2Ti_0.8)O₃; x = 0, 0.5, and 1.0 synthesized using solid-state reaction method are discussed in this work. The X-ray diffraction (XRD) process was used to examine the forming of a single-phase compound. The Rietveld refinements of XRD data were used in FullProf software to determine crystal symmetry, lattice parameters, and space groups. A scanning electron microscope was taken into use to examine the surface morphology of all of the samples. The samples' phase transition temperature was observed to lie between-10°C and 87°C, shifting toward the higher temperature side as x increased. In the case of x = 0.5, two-phase transitions were discovered at 22°C and 70°C. The value of impact generated output voltage and electrical energy increases as applied mechanical energy increases. The findings of this study point to the possibility of using 0.5(Ba_0.7Ca_0.3)TiO₃–0.5Ba (Zr_0.2Ti_0.8)O₃ ceramic for energy harvesting and sensing purposes.

Abstract: When a pure liquid crystal is dispersed into a suitable polymer to form micron-sized droplet, then it is called Polymer-dispersed liquid crystal (PDLC). In the present study, PDLC of different concentrations were prepared by dispersing a conducting polymer poly (3, 4–ethylenedioxy thiophene): poly (styrene sulfonate) into a cholestryl palmitate. The differential scanning calorimetry and fabry perot scattering studies were employed to study thermal and optical properties. It was found that the phase transition for PDLC occurs at a temperature different than those exhibited by pure liquid crystal. The behaviour of PDLC for parallel and perpendicular electric field has been investigated and the dielectric constant is determined. The value of dielectric constant and conductivity were found to increase with increasing concentration of polymer. The bistability and reflective properties of pure cholesteric liquid crystal can be minimized by dispersing polymer which makes material suitable for high contrast at large viewing angles.

Abstract: The microstructure, energy dispersive X-ray spectra, and field dependent polarization and electrostrictive strain characteristics of x(Ba_0.7Ca_0.3)TiO₃–(1-x)Ba (Zr_0.2Ti_0.8)O₃; x = 0, 0.5, and 1.0 synthesised using solid-state reaction process are discussed in this work. The X-ray diffraction process and scanning electron microscope were, respectively taken into use to examine the forming of single-phase compound and the surface morphology as well as elemental analyses of all of the samples. The grains sizes were found to lie between 3–12 μm and was largest for x = 0.5. The value of piezoelectric coefficient, converse piezoelectric effect (strain maximum to peak electric field), and electrostrictive coefficient were found to be the highest for x = 0.5 sample. Ba_0.85Ca_0.15Zr_0.10Ti_0.90O₃ was shown to be a potential lead-free electrostriction material for industrial applications, particularly in positioning actuators, based on field-dependent polarisation and strain experiments at ambient temperature.

Abstract: Barium strontium titanate (BST), Ba_0.8Sr_0.2TiO₃ ceramic prepared using conventional solid-state reaction method has achieved a single phase at 1400 °C. The Ba_0.8Sr_0.2TiO₃ ceramic shows the highest dielectric constant and capacitance at 65°C about 4001 (10 Hz) and 2.92765 x10^-9 F, respectively. The conductivity of Ba_0.8Sr_0.2TiO₃ ceramic is in between the range of semi-insulator and insulator materials, and this composition also has exhibited the positive temperature coefficient resistivity (PTCR) properties jump of one order of magnitude from 2.06202 x 10⁷ Ω.cm to 3.00958 x 10^8­ Ω.cm measured at 1 kHz.

Abstract: The 5 mol% Fe-doped BaTiO₃ ceramic has been synthesized by using solid-state method. The sample was characterized by X-ray diffraction (XRD) and Impedance spectroscopy. It is interesting to note that the sample can developed a phase transformation between 1000 °C to 1350 °C. The XRD results showed that sample exhibited cubic structure when heated at 1000 °C and developed oxygen non-stoichiometry when it was heated at 1350 °C for 8 hours. It was confirmed by the ceramic color changes. The dielectric properties of the sample is relatively low which is due to the oxygen non-stoichiometry effect and gives the dielectric constant, ε_r value around 150 at 30 °C with frequency 1 kHz. The capacitance value of this sample lies within 10^-8 to 10^-10 which represents that the electrical properties of the sample has shown bulk and grain boundary response. There are pores that can be observed from the SEM images indicates the porosity of the sample which is in a good agreement with the low dielectric constant value. Moreover, the grains are composed of rectangular orientations, hexagonal shapes and inhomogeneous microstructures that might represent the coexistence of tetragonal and hexagonal phase of the sample.

Abstract: The BaTi_0.88Zr_0.12O₃ ceramic has been synthesized by using a conventional solid-state reaction method and sintered at 1450 °C in air for 3 hours. The structural and dielectric properties of the sample were investigated. It was found that the sample exhibited tetragonal structure with space group P4mm. The maximum dielectric constant, ε_r value was obtained at T_c (70 °C) about 2800 measured at 1 kHz. The dielectric peak was broad which might be due to the pinching effect. However, maximum ε_r value was quite low may be attributed by the T_c and other phase transition point might be not fully coalescence. Another phase transition temperature was vaguely observed around 30 °C to 40 °C. The dielectric properties of the sample were dominated by the grain effect with capacitance values lie within range of 10^-10 to 10^-9. The SEM images shows that the average grain size of the sample was quite small about 2.9087 μm. It might be due to the contribution of Zr⁴⁺ with lower grain growth rate.

Abstract: The dielectric properties and crystal structure of Ba_0.85Sr_0.15TiO₃ and Ba_0.85Sr_0.15Ti_0.92Zr_0.08O₃ ceramics were studied. The samples were synthesized by using solid-state method. The results show that the samples were single phase. The Ba_0.85Sr_0.15TiO₃ exhibited tetragonal structure (space group P4mm), while with addition of 8 mol% Zr into Ba_0.85Sr_0.15TiO₃ it shows that the sample exhibited orthorhombic structure (space group Amm2). The dielectric constant value increased from 1094 for pure, up to 4211 for Ba_0.85Sr_0.15Ti_0.92Zr_0.08O₃ ceramic at T_c measured at 1 kHz. The T_c decreased from 80 °C down to 60 °C as 8 mol% Zr ions doped into Ba_0.85Sr_0.15TiO₃ composition. The Ba_0.85Sr_0.15Ti_0.92Zr_0.08O₃ ceramic exhibited lower dielectric loss, tan δ about 0.006 compared to Ba_0.85Sr_0.15TiO₃ ceramic (tan δ = 0.009) when measured at 110 °C with frequency 1 kHz. The slope at low frequency region in capacitance vs frequency plot for both samples attributed by the grain boundary effect, whereas the high frequency plateau associated with the bulk response. The impedance spectroscopy analysis results show that both samples are dominated by the bulk response when an incomplete semicircle arc was observed in Zʺ vs Zʹ plot.

Abstract: The BaTi_0.905Sn_0.095O₃ ceramic has been synthesized by using a solid-state method and sintered at 1450 °C in air for 3 hours. The doping effect of 9.5 mol% Sn into BaTiO₃ ceramic towards its crystal structure, dielectric properties and microstructure were investigated. The X-ray diffraction (XRD) analysis shows that the sample exhibited tetragonal structure with space group p4mm. The dielectric constant, ε_r measurement revealed that the sample reached the maximum ε_r value about 4393 when measured at T_c around 45 °C with frequency 1 kHz. The dielectric loss value was considerably low about below than 0.3 for the temperature range from 30 °C to 150 °C measured at 1 kHz. The capacitance value range lies between 10^-9 and 10^-10 indicates the bulk effect has dominated the electrical properties of the sample. It shows a good correlation with the microstructure results where the grains were well developed and homogenously distributed.

Abstract: In the present work, we have synthesized x [Co_0.9Ni_0.1Fe₂O₄]-(1-x) [0.5Ba_0.7Ca_0.3TiO₃-0.5BaZr_0.2Ti_0.8O₃], x = 0.3, 0.4 & 0.5 multiferroic composite by hydroxide co-precipitation method. The structural and morphological analysis of the composite was carried out by using X-ray diffraction and Scanning Electron Microscopy. The XRD spectra confirm the perovskite phase and spinel phase. Dielectric properties of the composite were studied using Impedance analyzer. The variation of dielectric constant and loss of tangent (Quality factor) in the frequency range of 100 Hz to 1 MHz were investigated. Magnetocapacitance were measured for magnetic field up to 1 Tesla, which increases with increase in magnetic field. Dielectric constant possesses contribution due to magnetic field dependent interfacial polarization and variation due to induced stress which can be explained on the observed MD effect. Saturation magnetization of composites increases with increase in CNFO content.