Enhancement Of Dielectric Permittivity Research Articles

Dielectric permittivity enhancement in hydroxyl functionalized polyolefins via cooperative interactions with water

Recent experiments have shown that polypropylene (PP) with a small fraction of hydroxyl (-OH) side groups displays a two-fold increase in the dielectric permittivity. It has been suggested that both the -OH groups and trapped water molecules may contribute to the dielectric constant increase. In this first principles computational study, using short polyolefin chains as models of PP, we shed light on the role played by -OH functional groups and the trapped moisture. Our results reveal that the trapped water molecules will inevitably accompany -OH incorporation (due to hydrogen bonding) and that both the -OH groups and water molecules will contribute cooperatively to the increase of the PP dielectric constant. These findings also provide insights into the effects of moisture on other molecularly functionalized materials systems.

Significant enhancements of dielectric and magnetic properties in Bi(Fe1−xMgx)O3−x/2 induced by oxygen vacancies

Bi(Fe1−xMgx)O3−x/2 (x = 0–10%) ceramics were synthesized by high-energy ball milling and solid-state reaction. It was found that a small amount of Mg doping leads to a dramatic enhancement in dielectric permittivity (∼two orders of magnitude), along with an apparent improvement in ferromagnetism. The observed significant enhanced dielectric properties may be interpreted by the Maxwell–Wagner relaxation in association with internal barrier layer capacitance. The ferromagnetism can be ascribed to the creation of unbalanced Fe3+ spins and relative long-range coupling mediated by the oxygen vacancies trapped localized electrons.

Enhanced Dielectric Permittivity of Nh<sub>4</sub>H<sub>2</sub>Po<sub>4</sub>/Polyvinyl Alcohol Composites at Low Percolation Threshold

A new kind of two phase ammonium dihydrogen phosphate (NH4H2PO4 or ADP)/polyvinyl alcohol (PVA) composite films have been prepared by solution cast technique. Significant enhancement of dielectric permittivity (~442) of ADP/PVA composites are observed at low ADP concentration (fADP fC ~5 wt %) which is the percolation threshold value estimated from the concentration dependent transport and dielectric data. Nearly 85 times increase in dielectric permittivity compared to that of the bare PVA film in the composite film around fC with low loss (~0.14) at 1 kHz and room temperature is observed. The present ADP based PVA composite material might be processed for application in devices.

Dielectric Stacking Effect of $\hbox{Al}_{2} \hbox{O}_{3}$ and $\hbox{HfO}_{2}$ in Metal–Insulator–Metal Capacitor

The dielectric stacking effects of Al2O3 and HfO2 thin layers in metal-insulator-metal capacitors are investigated for their leakage current, breakdown voltage, and voltage linearity of the dielectrics. The stacked dielectrics over three layers show the enhancement of dielectric permittivity and voltage linearity of quadratic voltage coefficient compared to one-layer dielectrics. Stacking over five layers attributes to improving leakage current density and breakdown voltage characteristics than three layers.

Influence of Fabrication Parameters on the Phase Formation and Dielectric Properties of CaCu3Ti4O12 Ceramics

The giant dielectric permittivity materials CaCu3Ti4O12 (CCTO) were synthesized by conventional solid-state reaction techniques. X-ray diffraction and Raman scattering for the powder indicate that the powder calcined at 950 °C for 12 h has been completely transformed into the purer CCTO phase. Furthermore, the morphology and size of the grains of the ceramics sintered at 1090 °C in the dwell time range from 0 to 26 h were observed by scanning electron microscopy (SEM). Dielectric properties of the polycrystalline CCTO ceramics were characterized in a broad frequency range (100 Hz–1 MHz) and at a temperature ranged from 300 to 500 K. The longer sintering time may lead to more defect structures and the enhanced conductivity, also leads to substantial improvements in permittivity. Grain size and density differences were not large enough to account for the enhancement in dielectric permittivity. Based on the observations, it is believed that the primary factor affecting dielectric behavior is the development of internal defects. The CCTO ceramics sintered at 1090 °C for 15 h exhibit lower dielectric loss (∼0.05) near room temperature, and the dielectric relaxation behavior above 1 kHz was observed to follow the Arrhenius law. The activation energy (Ea) of 0.65 eV indicates that the doubly ionized oxygen vacancies in the grain boundaries are responsible for the dielectric relaxation of the CCTO ceramics.

Structural and Electrical Characterization of Nanostructured a-SiNx:H PECVD Films

In order to correlate the material nano structure with the electrical properties of a-SiNx:H films a set of Si-rich SiNx films and M/I/S capacitors utilizing these films as dielectric layer were produced and characterized. The phase separation in the Si-rich SiNx films was studied by Raman spectroscopy and correlated with the variations in the dielectric permittivity (eox) and the effective charge in the dielectric layer, obtained by the C-V curves. As expected a dielectric permittivity enhancement in consequence of the silicon excess in the films was observed. The variation in the effective charge was correlated to the presence of silicon clusters in the films. The studied materials present high photoluminescence in the visible range and the next step is to investigate the electroluminescence in transparent electrode / SiNx/ Al-Si capacitors.

Stabilization of very high-k tetragonal phase in Ge-doped ZrO2 films grown by atomic oxygen beam deposition

Ge-doped ZrO2 thin films are prepared on SiON/Si substrates by atomic oxygen beam deposition. It is shown that, at low growth temperatures (225–360 °C) and by using only a low amount of Ge (3–6.2 at. %), it is possible to develop a pure tetragonal zirconia phase, which remains stable after 1050 °C annealing in N2. The dielectric permittivity (k) shows pronounced correlation with the structural details of the oxide film and is increasing with Ge content to a maximum value of 37.7, which is obtained for a 6.2 at. % Ge-doped sample grown at 225 °C. The dielectric permittivity enhancement upon doping is attributed to the increase in the ZrO2 tetragonal distortion, as inferred from x-ray diffraction data. Obtaining tetragonal ZrO2 with very high k-values at low deposition temperatures and with excellent thermal stability could be beneficial for the integration of this dielectric in scaled devices requiring low equivalent oxide thickness.

Spray deposited fluoropolymer/multi-walled carbon nanotube composite films with high dielectric permittivity at low percolation threshold

High performance perfluoro alkoxy (PFA) and chemical vapor deposition-grown multi-walled carbon nanotube (MWCNT) composite films with thicknesses of 30 μm were prepared using a scalable spray deposition technique. A homogeneous distribution of MWCNTs within the PFA matrix was confirmed by electron and optical microscopy. Dielectric and AC conductivity measurements showed a significant enhancement of dielectric permittivity for PFA/MWCNT films at low frequencies, and a very weak dependence of dielectric permittivity on temperature in the range 25–230 °C. Very low percolation threshold volume fractions of ca. 0.0043 and 0.0017 were attained for MWCNTs with two different aspect ratios, which have been explained by an inherent feature of spray route, a microcapacitor model and percolation theory. The combination of PFA/MWCNT composites and the spray deposition route provides a promising approach for the fabrication of industrial scale composite films with well-controlled dielectric properties for micro-electronic and high temperature applications.

Enhancement of dielectric permittivity in the ZnO/PZT ceramic matrix nanocomposites

Nanosized ZnO/lead zirconate titanate (ZnO/PZT) ceramic matrix composites were prepared by a traditional sintering process in this study. Dependence of the dielectric permittivity of the ZnO/PZT composites on frequency and temperature was studied. We observed the remarkable dependence of dielectric permittivity of the ZnO/PZT composites on the concentration of ZnO, frequency and temperature. A relatively high dielectric permittivity, which is more twice higher than that of pure PZT ceramics, was found in the ZnO/PZT composites. The results showed that the addition of nanosized ZnO had an obvious influence on the dielectric permittivity of the ZnO/PZT ceramics matrix composites.

Dielectric behavior of Nb-doped Ba(Zr xTi 1− x)O 3

Dielectric behavior of barium zirconate titanate, Ba(Zr 0.15Ti 0.85)O 3, relaxor ferroelectric ceramics doped with 0, 0.05, 0.10, and 0.15 mol% Nb 2O 5 was investigated to elucidate the mechanism of color variation of the ceramics due to both Nb 2O 5 content and sintering temperature between yellow and blue. The influence of Nb in BZT on dielectric properties has three effects. For small context Nb 2O 5, 0.05 mol%, the dielectric permittivity of the specimen sintered at 1250 °C reaches 7500. The enhancement of dielectric permittivity can be interpreted as the space charge from a double-well potential in NbO 6 octahedra. For 0.10 mol%, dielectric permittivity of the blue sample approaches 17,000, dielectric loss is large too, and the relaxor behavior is much more prominent. The result of XPS measurement shows that the binding energy of Ti 2p 3 for blue specimen deceases, which implicates an alteration of Ti 4+ → Ti 3+. For 0.15 mol% Nb 2O 5-doped Ba(Zr 1− x Ti x )O 3, the deep yellow sample one, both dielectric parameters become very small illustrating the forming of a new yellow system BaTiO 3–Ba 0.5NbO 3.

Structural correlations of the enhancement of dielectric permittivity in the (Ta2O5)0.92(TiO2)0.08 system

A Ti-ion ordering which correlates to the significant enhancement of the dielectric constant was determined in the (Ta2O5)0.92(TiO2)0.08 system by high resolution electron microscopy and the corresponding simulations. The alien Ti ions were determined to selectively sit on the octahedral locations in the Ta2O5 base structure in an average of 9-time period along the ⟨110⟩ direction. The authors suggest this Ti-ion ordering induces the directional enhancement of the dielectric permittivity of the (Ta2O5)0.92(TiO2)0.08 system. The atomic mechanism of this modulated structure contributing to the enhancement of the dielectric constant was qualitatively interpreted using a one-dimensional chain model. The structural correlations of the dielectric enhancement revealed in this study suggest a way to search or design high-k materials.

Dielectric Permittivity Enhancement in PZT by Light Doping with Gd

ABSTRACTPbZr0.53Ti0.4703 doped with 0.6% at. of Gd2O3 has been produced following the traditional solid state reaction technique. The ferro-paraelectric transition temperature is reduced from 386 °C to 352 °C. Remnant polarization and coercive field measurements were made from the hysteresis loops obtained at 23 °C and at different applied electric fields up to a maximum of 17 kV/cm. Piezoelectric performance was studied in the 4 Hz to 4 MHz frequency range at 25 °C and the radial electromechanical coupling factor was determined. A detailed electrical conductivity study in the 30-450 °C temperature range is performed in a wide frequency interval. The different participating transport mechanisms are elucidated and the corresponding activation energies were determined by fitting the experimental data. In particular, in the 30 to 300 °C temperature interval, the ac conductivity follows Jonscher universal relaxation law.

Processing, Investigation of Structure, Microstructure, Dielectric and Piezoelectric Properties of PbMg1/3Nb2/3O3-PbTiO3 Ceramics Doped with the PbMg1/2W1/2O3 Additive

The ceramic compositions near the morphoptropic boundary of the systems Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 (PMN-PT) and Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 -Pb(Mg 1/2 W 1/2 )-O 3 (PMN-PT-PMW) have been prepared using the high disperse magnesium oxide precursor. Domain structure and piezoelectric hysteresis loops have been studied by the piezoelectric force microscopy (PFM) method. Ordering of the domain patterns has been revealed in the PMW doped ceramics. The decreasing of the ferroelectric phase transition temperature, while the enhancement of dielectric permittivity and piezoelectric d 33 and | d| 31 coefficients has been shown to be governed by the PMW content.

The Interpretation of Dielectric Spectroscopy Measurements on Silica and Hematite Sols

Experimental data on the dielectric response of silica and hematite sols from the literature are interpreted using an analytical theory developed previously (Chassagne, C., Bedeaux, D., and Koper, G. J. M., J. Phys. Chem B 105, 11,743 (2001), and Physica A, to be published). The theory is found to correctly predict both the relaxation frequency and the dielectric permittivity enhancement at low frequencies with only one free parameter. This parameter can be the zeta potential or the Stern layer conductance, in the case that the zeta potential is fixed to agree with the electrophoretic mobility measurements.

Maxwell-Wagner relaxation in piezoactive media

Maxwell-Wagner piezoelectric, dielectric and elastic relaxations in two-layer or multilayer serial piezoactive media are considered. As distinct from the oversimple model, described in literature, we derive exact solutions by taking into account mechanical boundary conditions, transversal piezoelectric response and elastic properties of layers. We first study the Maxwell-Wagner relaxation of elastic compliances and the contribution from piezoelectric coefficients and elastic constants of two layers to the value of the relaxation time. Methods for strengthening as well as eliminating the relaxations and for the giant enhancement of dielectric permittivity are specially reviewed.