Narrow Results

The primary aim of the current research is to explore the impact of yttrium-doping in barium stannate titanate (Ba${}_{1-1.5x}$Y_xTi${}_{1-z}$Sn_zO₃) to investigate the variation in its structural and electrical properties. The specimens were synthesized using a solid-state method, wherein the precursors were heated together until they reacted to form the desired compounds. Subsequently, X-ray diffractometric analysis was employed to confirm the crystallographic phases. Archimedes’ method was used to determine the density of the material. An Electron Paramagnetic Resonance (EPR) study was conducted to examine the nature of defect centers and impurity ions within the synthesized ceramics. Furthermore, the impact of yttrium (Y) substitution on the system’s morphology and grain growth was evaluated through SEM micrographs. Selective compositions were found with enhanced dielectric properties of barium titanate ceramic, exhibiting a dielectric constant of 9816 at the transition point. The highest value among all studied samples had a clear indication of DC conductivity. Piezoelectric coefficient (d${}_{33}$) and P-E hysteresis loops were also investigated for these samples, indicating potential applications in electronic devices for the modified material’s improved ferroelectric properties.

The challenges in productivity of satellite mobile devices are growing rapidly to overcome the question of miniaturization. The intention is to supply the electrical and microwave properties of materials by discovering their outstanding electronic properties. Neodymium Zinc Titanate (NZT) can be a promising ferroelectric material due to its stable dielectric and microwave properties. The grain size and shape of NZT have a strong influence on overall material performances. Therefore, shape, reconstruction and property of the coming compound take an important part and can be predicted before being utilized in the devices. The significant of this research is to define ferroelectric properties of NZT and to characterize it by using Fractal Nature Analysis (FNA). FNA is a powerful mathematical technique that could be applied to improve the grain shape and interface reconstruction. The fractal structure is identified by its self-similarity. The self-similarity of an object means a repetition of shapes in smaller scales. A measure of this structure is computed using the Hausdorff dimension. It is for the first time in this investigation the Fractal analysis method is applied for the microwave materials microstructure reconstruction which makes this research an innovative work and will open the door for Curie–Weiss law fractal correction. In connection to our previous research for dielectric properties fractalization, we had some characterization and reconstruction data which include the Hausdorff dimension (HD).

Transparent 3Na₂O–6.5B₂O₃ (NBO) glasses were fabricated via the conventional melt-quenching technique. X-ray powder diffraction (XRD) combined with Differential Scanning Calorimetric (DSC) studies carried out on the as-quenched samples confirmed their amorphous and glassy nature, respectively. The frequency and temperature dependent of the dielectric constant, electric modulus and electrical conductivity of the transparent NBO glasses were investigated in the 100 Hz–10 MHz frequency range. The electrical modulus and conductivity data have been rationalized using Jonscher's universal law. The bulk dc conductivity at various temperatures was extracted from the electrical relaxation data. The activation energy associated with dc conductivity is 0.52 ± 0.01eV, which is ascribed to the motion of Na⁺ ions in the glass matrix.

Solid solutions based on Li, Ta and Sb-doped (K_0.5Na_0.5)NbO₃ (KNN) lead-free perovskite systems were created using standard solid-state methods. X-ray diffraction was used to confirm that all compositions were single phase and to verify the phase transition from tetragonal to cubic at T_C = 302°C. The three compositions examined, originally developed by Saito and Li, were shown to be strongly ferroelectric with sharp peaks in permittivity present at the Curie temperature. The optimum composition had loss tangent values below 5% up to 100 kHz at room temperature. Bipolar hysteresis measurements showed high values for both maximum polarization (25 and 21 μC/cm²) and remenant polarizations (20 and 16 μC/cm²) for undoped and 0.2 wt% CuO-doped samples. Maximum strain values of greater than 0.23% were observed.

Environment friendly ferroelectric relaxor Ba(Zr_0.2Ti_0.8)O₃ thin films with the addition of 2% Mn dopant were grown on (001) MgO substrates by pulsed laser deposition. Microstructure studies with X-ray diffraction and transmission electron microscopy reveal that the as-grown Ba(Zr_0.2Ti_0.8)O₃ thin films are c-axis oriented with an atomic sharp interface. The films have good single crystallinity and good epitaxial quality. The interface relationship was determined to be [100]_Mn:BZT//[100]_MgO and (001)_Mn:BZT//(001)_MgO. Nanoscale order/disorder relaxor structures were found with nano-columnar structures. The microwave dielectric measurements (15–18 GHz) indicate that the films have excellent dielectric properties with large dielectric constant value, high tunability, and low dielectric loss, promising the development of room temperature tunable microwave elements.

Chlorophyll a (naturally occurring Mg porphyrene) has been entrapped in nano/porous silica gel using sol–gel method at room temperature, producing a stable composite. HRTEM observation reveals regular nanoscale [around 15–20 nm diameter] distribution of aggregated polycrystalline chlorophyll a within porous silica matrix. UV-vis study also corroborates the presence of various aggregated chlorophyll a species within the system. Low field measurement shows almost 400 times enhancement of dielectric constant (1700) with incorporation of only 0.125 mg/ml of chlorophyll and the loss is 0.5 at room temperature at 100 Hz. The dielectric constant of the composite reaches 2500 as chlorophyll concentration becomes 1 mg/ml. Observed strong space charge response to the external field and strong frequency dispersion of the dielectric properties of the composite can be attributed to the long-range electron delocalization [nomadic polarization] in chlorophyll a aggregates. The electric modulus (M*) formalism used in this study enabled us to distinguish and separate various relaxation processes. It is found that with increasing chlorophyll concentration D.C. relaxation time decreases exponentially at room temperature. It is shown that observed relaxations do not perfectly follow the Debye response in high frequency region due to heterogeneous distribution of chlorophyll aggregates. The low values of room temperature activation energy calculated from Arrhenius plot reveal that polaronic hopping phenomena is absent at grain-interfacial region due to low thermal energy.

The glasses in the system (100 - x)TeO₂–xCaCu₃Ti₄O₁₂, (x = 0.25 mol.% to 3 mol.%) were fabricated. The color varied from olive green to brown as the CaCu₃Ti₄O₁₂ (CCTO) content increased in TeO₂ matrix. The X-ray powder diffraction and differential scanning calorimetric analyses that were carried out on the as-quenched samples confirmed their amorphous and glassy nature respectively. The dielectric constant and loss in the 100 Hz–1 MHz frequency range were monitored as a function of temperature (50–400°C). The dielectric constant and the loss (D) increased as the CCTO content increased in TeO₂ at all the frequencies and temperatures under investigation. Further, the and D were found to be frequency-independent in the 50–200°C temperature range. The value obtained for the loss at 1 MHz was 0.0019 which was typical of low loss materials, and exhibited near constant loss (NCL) in the 100 Hz–1 MHz frequency range. The electrical relaxation was rationalized using the electric modulus formalism. These glasses may be of considerable interest as substrates for high frequency circuit elements in conventional semiconductor industries owing to their high thermal stability.

Polycrystalline SrBi₄Ti_3.975Zr_0.025O₁₅ (SBTZ) was prepared using solid-state reaction technique. SBTZ was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD analysis indicated the formation of a single-phase orthorhombic structure. Particle size was found using SEM. The dielectric, ferroelectric, piezoelectric, modulus and impedance spectroscopy studies on SBTZ were investigated in the frequency range 1 Hz–1 MHz from room temperature (RT) to 600°C. Piezoelectric charge and electromechanical coupling coefficients were calculated from resonance and anti-resonance frequencies. Impedance and modulus plots were used as tools to analyze the sample behavior as a function of frequency. Cole–Cole plots showed a non-Debye relaxation. Conductivity measurements were performed on SBTZ.

In this work, nanocomposites (poly(vinylidenefluoride–trifluoroethylene–chlorotrifluoroethylene)/Graphene nanosheets) (P(VDF–TrFE–CTFE)/GNS) were fabricated via solution cast process. GNS were covalently functionalized with KH550 to improve their interfacial interactions with the terpolymer matrix P(VDF–TrFE–CTFE). Compared to neat terpolymer, significantly improved dielectric permittivity and low loss were observed for the composites. For instance, at 1 kHz the P(VDF–TrFE–CTFE)/GNS composites with 4% GNS possessed a dielectric permittivity of 144, over 14 times larger than that of neat terpolymer, while the loss was only 0.56. These findings represent an effective route to design potential dielectric polymer films for high-charge storage capacitors.

CaCu₃Ti₄O₁₂ (CCTO) ceramics which has perovskite structure gained considerable attention due to its giant permittivity. But it has high tan δ (0.1 at 1 kHz) at room temperature, which needs to be minimized to the level of practical applications. Hence, TeO₂ which is a good glass former has been deliberately added to CCTO nanoceramic (derived from the oxalate precursor route) to explore the possibility of reducing the dielectric loss while maintaining the high permittivity. The structural, morphological and dielectric properties of the pure CCTO and TeO₂ added ceramics were studied using X-ray diffraction, Scanning Electron Microscope along with Energy Dispersive X-ray Analysis (EDX), spectroscopy and Impedance analyzer. For the 2.0 wt.% TeO₂ added ceramics, there is a remarkable difference in the microstructural features as compared to that of pure CCTO ceramics. This sample exhibited permittivity values as high as 7387 at 10 KHz and low dielectric loss value of 0.037 at 10 kHz, which can be exploited for the high frequency capacitors application.

Temperature and electric field dependences of the dielectric behavior and phase transition for [111]-oriented 0.23PIN–0.52PMN–0.25PT (PIN-PMN–0.25PT) and 0.24PIN–0.43PMN–0.33PT (PIN–PMN–0.33PT) single crystals were investigated over a temperature range from -100°C to 250°C using field-heating (FH) dielectric measurements. The transition phenomenon from ferroelectric microdomain to macrodomain was found in rhombohedra (R) phase region in the single crystals under dc bias. This transition temperature T_f of micro-to-macrodomain is sensitive to dc bias and move quickly to lower temperature with increasing dc bias. The phase transition temperatures in the two single crystals shift toward high temperature and the dielectric permittivities at the phase transition temperature decrease with increasing dc bias. Especially, the phase transition peaks are gradually broad in PIN–PMN–0.33PT single crystal with the increasing dc bias. Effects of dc bias on the dielectric behavior and phase transition in PIN–PMN–PT single crystals are discussed.

Yttrium Copper Titanate (Y_2/3Cu₃Ti₄O₁₂) nanoceramic is structurally analogous to CaCu₃Ti₄O₁₂ (CCTO). X-ray diffraction (XRD) of Y_2/3Cu₃Ti₄O₁₂ (YCTO) shows the presence of all normal peaks of CCTO. SEM micrograph exhibits the presence of bimodal grains of size ranging from 1–2 μm. Bright field TEM image clearly displays nanocrystalline particle which is supported by presence of a few clear rings in the corresponding selected area electron diffraction (SAED) pattern. It exhibits a high value of dielectric constant (ε′ = 8434) at room temperature and 100 Hz frequency with characteristic relaxation peaks. Impedance and modulus studies revealed the presence of temperature-dependent Maxwell–Wagner type of relaxation in the ceramic.

Breakthroughs can be expected in multi-component ceramics by adjusting the phase assembly and the micro–nanostructure. Controlling the architecture of multi-materials at different scales is still challenging and provides a great opportunity to broaden the range of functionalities in the field of ferroelectric-based ceramics. We used the potentialities of Spark Plasma Sintering (SPS) to control a number of key parameters regarding the properties: anisotropy, interfaces, grain size and strain effects. The flexibility of the wet and supercritical chemistry routes associated with the versatility of SPS allowed designing new ferroelectric composite ceramics at different scales. These approaches are illustrated through various examples based on our work on ferroelectric/dielectric composites.

xPb(In_1/2Nb_1/2)O₃-Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃(xPIN–yPMN–zPT) ternary ceramics with morphotropic phase boundary (MPB) composition were synthesized by columbite precursor method. xPIN–yPMN–zPT phase diagram was investigated by x-ray diffraction and dielectric measurements. According to the results of dielectric measurements, the Curie temperatures (T_c) and rhombohedral to tetragonal phase transition temperature (T_r−t) were found to be in the range of 173–212°C and 114–155°C, respectively, indicating that the T_r-t was increased with adding PIN component. In the MPB region, the highest T_r-t = 155°C was found in 0.32PIN–0.38PMN–0.30PT ceramic, that greatly expanded temperature usage range.

The dielectric integrity has been one of the major obstacle in bringing out capacitor devices with suitable performance characteristics at high temperatures. In this paper, B_xN_yO_z dielectric films for high temperature capacitors solutions are investigated. The films were grown on silicon substrate by using ion source assisted physical vapor deposition technique. The as-grown films were characterized by SEM, XRD, and XPS. The capacitor structures were fabricated using B_xN_yO_z as a dielectric and titanium as metal electrodes. The elaborated devices were subjected to electrical and thermal characterization. They exhibited low electrical loss and very good stability when subjected to high temperature for a prolonged period of time.

The temperature coefficient of permittivity ($\mathrm{\text{TC}}\epsilon$) of BaTiO₃–Bi(Me)O₃ solid solutions were investigated. It was determined that as the tolerance factor was decreased with the addition of Bi(Me)O₃, the $TC\epsilon$ shifted from large negative values to $\mathrm{\text{TC}}\epsilon$ values approaching zero. It is proposed that the different bonding nature of the dopant cation affects the magnitude and temperature stability of the permittivity. This study suggests that the relationship between tolerance factor and $\mathrm{\text{TC}}\epsilon$ can be used as a guide to design new dielectric compounds exhibiting temperature-stable high permittivity characteristics, which is similar to past research on perovskite and pyrochlore-based microwave dielectrics.

Conductor–dielectric 0–3 nanocomposites using spherical nickel nanoparticles as filler and poly(vinylidene fluoride–trifluoroethylene) 70/30mol.% as matrix are prepared using a newly developed process that combines a solution cast and a hot-pressing method with a unique configuration and creates a uniform microstructure in the composites. The uniform microstructure results in a high percolation threshold ${\phi }_c$ ($>55$ vol.%). The dielectric properties of the nanocomposites at different frequencies over a temperature range from $-$70${}^{\circ }$C to 135${}^{\circ }$C are studied. The results indicate that the composites exhibit a lower electrical conductivity than the polymer matrix. It is found that the nanocomposites can exhibit an ultra-high dielectric constant, more than 1500 with a loss of about 1.0 at 1kHz, when the Ni content (53 vol.%) is close to percolation threshold. For the nanocomposites with 50 vol.% Ni particles, a dielectric constant more than 600 with a loss less than 0.2 is achieved. It is concluded that the loss including high loss is dominated by polarization process rather than the electrical conductivity. It is also found that the appearance of Ni particles has a strong influence on the crystallization process in the polymer matrix so that the polymer is converted from a typical ferroelectric to a relaxor ferroelectric. It is also demonstrated that the widely used relationship between the dielectric constant and the composition of the composites may not be valid.

This work prepares (Ba${}_{0.5}$Sr${}_{0.5}$)TiO₃ (BST)-doped (Bi${}_{1∕2}$Na${}_{1∕2}$)TiO₃ (NBT) lead free ceramics through conventional solid reaction method and analyzes the doping effect of BST on phases, microstructure, dielectric and ferroelectric properties. The phase and structure of the NBT-BST ceramics were investigated through X-ray diffractometer (XRD) and Raman. The XRD results showed that BST has diffused into the NBT lattices to form a stable solid solution; while, Raman spectrum showed the bands at low frequency are different with that of pure NBT and divided into two ranges around 247cm${}^{-1}$ and 303cm${}^{-1}$. Relative dense and homogeneous ceramic microstructures could be achieved, with the observation of a slight decrease in average grain size with the increase of BST doping content. The dielectric and ferroelectric properties were also investigated. The dielectric constant increases gradually with increasing the temperature to $T_{\mathrm{\text{m}}}$, and then decrease. The temperature dependence property showed diffused phase transition near $T_{\mathrm{\text{m}}}$. The polarization-electric field ($P$-$E$) hysteresis loops of BST-doped NBT ceramics showed typical ferroelectric or relaxor nature. Both the $E_{\mathrm{\text{c}}}$ and $P_{\mathrm{\text{r}}}$ increased first, then decreased with respect to the increase of the BST content.

Lead-free sodium–potassium niobate-based piezoelectric materials are most intensively studied in order to replace the widely used Pb-based ones. In this work, the effects of modification of compositions by donor and acceptor dopants in the A- and B-sites of perovskite lattice on structure, dielectric, ferroelectric, and piezoelectric properties of ceramics from Morphotropic Phase Boundary in the ($1-x$)(K${}_{0.5}$Na${}_{0.5}$)NbO₃–$x$BaTiO₃ system and in compositions with $x=0.05$ and 0.06 additionally doped by Ni${}^{3+}$ cations have been studied.

In this work, we report the dielectric properties of Single wall Carbon Nanotubes (SWCNTs)-based phantom that is mainly composed of gelatin and water. The fabricated gelatin-based phantom with desired dielectric properties was fabricated and doped with different concentrations of SWCNTs (e.g., 0%, 0.05%, 0.10%, 0.15%, 0.2%, 0.4% and 0.6%). The dielectric constants (real ${\epsilon }^{\prime }$ and imaginary ${\epsilon }^{\prime \prime })$ were measured at different positions for each sample as a function of frequency (0.5–20GHz) and concentrations of SWCNTs and their averages were found. The Cole–Cole plot (${\epsilon }^{\prime }$ versus ${\epsilon }^{\prime \prime })$ was obtained for each concentration of SWCNTs and was used to obtain the static dielectric constant ${\epsilon }_s$, the dielectric constant at the high limit of frequency ${\epsilon }_{\infty }$ and the average relaxation time $\tau$. The measurements showed that the fabricated samples are in good homogeneity and the SWCNTs are dispersed well in the samples as an acceptable standard deviation is achieved. The study showed a linear increase in the static dielectric constant ${\epsilon }_s$ and invariance of the average relaxation time $\tau$ and the value of ${\epsilon }_{\infty }$ at room temperature for the investigated concentrations of SWCNTs.