Dielectric loss

About: Dielectric loss is a research topic. Over the lifetime, 20296 publications have been published within this topic receiving 349254 citations.

Resonant domain-wall-enhanced tunable microwave ferroelectrics

Abstract: Ordering of ferroelectric polarization1 and its trajectory in response to an electric field2 are essential for the operation of non-volatile memories3, transducers4 and electro-optic devices5. However, for voltage control of capacitance and frequency agility in telecommunication devices, domain walls have long been thought to be a hindrance because they lead to high dielectric loss and hysteresis in the device response to an applied electric field6. To avoid these effects, tunable dielectrics are often operated under piezoelectric resonance conditions, relying on operation well above the ferroelectric Curie temperature7, where tunability is compromised. Therefore, there is an unavoidable trade-off between the requirements of high tunability and low loss in tunable dielectric devices, which leads to severe limitations on their figure of merit. Here we show that domain structure can in fact be exploited to obtain ultralow loss and exceptional frequency selectivity without piezoelectric resonance. We use intrinsically tunable materials with properties that are defined not only by their chemical composition, but also by the proximity and accessibility of thermodynamically predicted strain-induced, ferroelectric domain-wall variants8. The resulting gigahertz microwave tunability and dielectric loss are better than those of the best film devices by one to two orders of magnitude and comparable to those of bulk single crystals. The measured quality factors exceed the theoretically predicted zero-field intrinsic limit owing to domain-wall fluctuations, rather than field-induced piezoelectric oscillations, which are usually associated with resonance. Resonant frequency tuning across the entire L, S and C microwave bands (1-8 gigahertz) is achieved in an individual device-a range about 100 times larger than that of the best intrinsically tunable material. These results point to a rich phase space of possible nanometre-scale domain structures that can be used to surmount current limitations, and demonstrate a promising strategy for obtaining ultrahigh frequency agility and low-loss microwave devices.

Highly stretchable dielectric elastomer composites containing high volume fractions of silver nanoparticles

Abstract: The dielectric permittivity (e′) of a polymeric material can be significantly increased when blended with conductive fillers at concentrations approaching the percolation threshold. However, reproducible synthesis of such composites is after decades of research still a major challenge and a bottleneck for their application. Difficulties arise in controlling the size and shape of the filler as well as in its homogenous distribution within the composite. These parameters strongly affect the dielectric as well as mechanical properties of the composite. While a substantial amount of literature deals with the influence of conductive fillers on the dielectric properties of composites, little is known about their mechanical properties. It is therefore still an important goal to synthesize materials with simultaneously high e′ and good mechanical properties. Here, we report the synthesis of dielectric elastomers that combine key properties such as high flexibility and stretchability, high thermal stability, increased e′, low dielectric loss and conductivity. Such materials were prepared by solution processing using quasi-spherical silver nanoparticles (AgNPs) of a defined size in a polydimethylsiloxane matrix (Mw = 692 kDa). To prevent percolation, the AgNPs were coated with a thin silica shell (<4 nm). To increase their compatibility with the silicone matrix, these core–shell nanoparticles were passivated with a silane reagent. The insulating silica shell around the particles precisely defines the minimum approach distance between the cores as twice the shell thickness. The dielectric properties of the passivated particles (filler) were measured in pellets and found to have an almost frequency independent value of e′ = 90 and a very low loss factor tan δ = 0.023 at high frequencies. When such particles were used as fillers in a polydimethylsiloxane matrix, composites with low dielectric losses were obtained. A composite containing a 31 vol% filler with e′ = 21 and tan δ = 0.03 at ∼1 kHz was achieved. At a AgNP volume fraction of 20%, the composite has e′ = 5.9 at ∼1 kHz, a dielectric strength of 13.4 V μm−1, an elastic modulus as low as 350 kPa at 100% strain, and a strain at break of 800%. Due to the high specific energy density per volume at low electric fields, these composites are attractive materials in applications involving low electric fields.

Dielectric Ceramics with Tungsten-bronze Structure in the BaO–Nd2O3–TiO2–Nb2O5 System

Abstract: Some tungsten-bronze compounds in the BaO–Nd2O3–TiO2–Nb2O5 system were prepared and characterized. Ba4Nd2Ti4Nb6O30 and Ba5NdTi3Nb7O30 had the filled tetragonal tungsten-bronze structure, and Ba3Nd3Ti5Nb5O30 consisted of the tetragonal tungsten-bronze major phase and a minor amount of secondary phase BaNd2Ti3O10. These compounds had significant relaxor behaviors, and the Curie temperatures (at 1 MHz) were 0 and 55 °C for Ba3Nd3Ti5Nb5O30 and Ba5NdTi3Nb7O30 ceramics, respectively. A high dielectric constant (213) combined with low dielectric loss (0.004 at 1 MHz) was obtained in Ba3Nd3Ti5Nb5O30 ceramics. In addition, the solid-solution range of BapNd6−pTi8−pNb2+pO30 was 3 < p ≤ 6.