Stable Permittivity Research Articles

Structural and Dielectric Properties of Bi (Mg1/2Ti1/2)O3–BaTiO3 Lead‐Free Ceramics

By the conventional mixed oxide method (1−x)Bi(Mg1/2Ti1/2)O3–xBaTiO3 ((1−x)BMT–xBT, x = 0.2−1.0) ceramics were prepared. For x ≤ 0.4, a bismuth‐rich phase was observed beside the perovskite phase. For 0.5 ≤ x ≤ 0.92 ceramics, all the compositions belong to the pseudocubic phase, while the tetragonal phases were formed when x ≥ 0.94. With the increase of BT content, a change from a relaxor‐like behavior to a normal ferroelectric behavior was observed, while the change of Tmax is in the form of “U” curve. Furthermore, stable dielectric permittivity (1500–3000) and low losses (tan δ < 2%) were obtained in the 0.4 ≤ x ≤ 0.6 ceramics in the temperature range 200°C–400°C, indicating a potential for high‐temperature applications.

Effects of molecular functionalization sequence on mesoporous silica film properties

Functionalizing mesoporous silica (MPS) films with multiple organosilanes is attractive for tailoring stable low permittivity (low k) dielectrics for nanodevice wiring applications. Here, the authors show that the organosilane treatment sequence can have a strong influence on MPS film proper-ties. Films functionalized first with trimethylchlorosilane (TMCS), followed by bis[3-(triethoxysilyl)propyl] tetrasulfide (BTPTS) treatment, exhibit lower k, lower leakage currents, and lower stress compared with films with the functionalization sequence reversed. The observed behavior is due to inhibited water uptake arising from the higher effectiveness of TMCS than BTPTS to passivate silanol groups on pore walls. These findings are relevant in realizing high-stability low k dielectrics for nanodevice wiring.

High Stability of Dielectric Permittity for K0.5Na0.5NbO3-Based Lead Free Piezoelectric Ceramics

A new perovskite ferroelectric, Bi(Mg2/3Nb1/3)O3, was proposed to develop Na0.5K0.5NbO3(KNN)-based lead-free piezoelectric ceramics by an conventional preparation technique. Dielectric stability properties of lead-free K0.5Na0.5NbO3- Bi(Mg2/3Nb1/3)O3 ceramics were studied. The addition of BMN leads to a polymorphic phase transition between ferroelectric orthorhombic and rhombohedral phases(x = 0.01). 0.03BMN-0.97KNN ceramics show a broad and stable permittivity maximum near 1450 from 25 to 400°C and lower dielectric loss(≤5%) at broad temperature usage range 25–400°C for diffusion phase transition. The results indicate that this material may have great potential for high temperature capacitors in automobile applications.

A NEW MICROWAVE METHOD BASED ON TRANSMISSION SCATTERING PARAMETER MEASUREMENTS FOR SIMULTANEOUS BROADBAND AND STABLE PERMITTIVITY AND PERMEABILITY DETERMINATION

A new microwave method has been proposed for simultaneous broadband and stable complex permittivity and complex permeability determination of magnetic and nonmagnetic materials. The method utilizes complex transmission scattering measurements at difierent frequencies. For a change in constitutive parameters determination, we considered zero-order and higher- order approximations. We have verifled the proposed method from measurements of two medium- and low-loss materials with another method and available reference data in the literature.

Shape Memory Piezoelectric Actuator by Control of the Imprint Electrical Field

The fundamental study of a shape memory piezoelectric actuator was conducted, using operated with a pulsed voltage, so that low energy consumption and low voltage operation could be realized. To realize the shape memory operation of the piezoelectric actuator, an imprint electrical field was induced with a high electrical field of 3.5 kV/mm in a 150°C environment. The memory effect of the displacement and the permittivity of the shape memory piezoelectric actuator resulted from the asymmetric butterfly curve caused by the imprint electrical field. The actuator has two stable strain conditions and permittivity values that were dependent on the direction of polarization, imparting the shape memory effect and permittivity memory effect. Furthermore, self-sensing operation was realized by detection of the permittivity that corresponds to the position of the actuator.

High Tm lead-free relaxor ferroelectrics with broad temperature usage range: 0.04BiScO3−0.96(K0.5Na0.5)NbO3

In order to develop high temperature lead-free relaxors, xBiScO3−(1−x)(K0.5Na0.5)NbO3[xBS−(1−x)KNN] ceramics were proposed using a tolerance factor approach. To verify this proposal, xBS−(1−x)KNN ceramics were synthesized by conventional solid-state sintering. A stable perovskite phase was obtained when KNN content was greater than 96 mol %. The diffuse phase transition and frequency dispersion of the dielectric constant, which are two typical characteristics of relaxor ferroelectrics, were observed in xBS−(1−x)KNN ceramics. The dielectric relaxor behavior follows a modified Curie–Weiss law relationship. In addition, 0.04BS-0.96KNN ceramics show a broad and stable permittivity maximum near 2500 from 100 to 300 °C and lower dielectric loss (<5%) at broad temperature usage range (100–300 °C). The results indicate that this material may have great potential for high temperature capacitors in automobile applications.

Stable Polymer Dielectric Film for Polythiophene Thin Film Transistor on Modified Poly(vinyl phenol) with Polar Functional Group

In this work, a modified poly(vinyl phenol) (MPVP) polymer dielectric solution with high permittivity and resistant to moisture was used. The MPVP was synthesized by replacing the hydroxyl group in PVP with a polar amino functional group. The material properties of polymer films were characterized by nuclear magnetic resonance (NMR) analysis, gel permeation chromatography (GPC), and thermogravimetric analysis (TGA). Dielectric layers properties were analyzed by current–voltage and capacitance–voltage measurement of a metal–dielectric–metal capacitor and a polythiophene (P3HT) polymer transistor. The stable leakage current, permittivity and output characteristic indicate that MPVP is suitable for a large-area continues-printing process.

Frequency Dependence of the Complex Permittivity and Its Impact on Dielectric Sensor Calibration in Soils

The capacitance (CAP) method and time domain reflectometry (TDR) are two popular electromagnetic techniques used to estimate soil water content. However, the frequency dependence of the real and imaginary part of the permittivity complicates sensor calibration. The frequency dependence can be particularly significant in fine-textured soils containing clay minerals. In this work, we applied both the CAP method and TDR to a nondispersive medium (fine sand) and a strongly dispersive medium (bentonite). The measurements were conducted for a range of water contents. Results using a network analyzer showed that the frequency dependence of the real permittivity of the bentonite was particularly strong below 500 MHz. Above this frequency, the real permittivity of the bentonite was mainly a function of the water content. The TDR predicted apparent permittivity in the bentonite was below the CAP predicted real permittivity at low water contents. This was attributed to the dispersive nature of the bentonite combined with the high frequency of operation of TDR (up to 3 GHz in dry soil). The CAP sensor (frequency of 100-150 MHz) overestimated the real permittivity of the bentonite at high water contents. An electric circuit model proved partially successful in correcting the CAP data by taking the dielectric losses into account. The TDR signal became attenuated at higher water contents. It seems worthwhile to raise the effective frequency of dielectric sensors above 500 MHz to benefit from the relatively stable permittivity region at this frequency.

Novel Linear and Cross-Linked Acrylate Polymers Bearing O-Cyanoethylated (Glycosyloxy)ethyl Side Chain with High Dielectric Properties over Wide Temperature Range

Abstract UV-irradiation (365 nm) on a spreaded mixture of 2-[tetra-O-(cyanoethyl)glucopyranosyloxy]ethyl acrylate and ethylene glycol dimethacrylate onto a copper plate gave a cross-linked copolymer which exhibited extremely stable and high dielectric permittivity (ε′) of 23 to 30 (−100 to −10 °C) and as high as 49 even at 20 °C.