Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userPolar nano-clusters in nominally paraelectric ceramics demonstrating high microwave tunability for wireless communication
544
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Dielectric materials, with high tunability at microwave frequencies, are key components in the design of microwave communication systems. Dense Ba0.6Sr0.4TiO3 (BST) ceramics, with different grain sizes, were prepared in order to optimise the dielectric tunability via polar nano cluster effects. Dielectric permittivity and loss measurements were carried at both high and low frequencies and were supported by results from X-ray powder diffraction, scanning and transmission electron microscopies, Raman spectroscopy and piezoresponse force microscopy. The concentration of polar nano clusters, whose sizes are found to be in the range 20 to 50 nm, and the dielectric tunability increase with increasing grain size. A novel method for measurement of the microwave tunability in bulk dielectrics is presented. The highest tunability of 32% is achieved in ceramics with an average grain size of 10 um. The tunability of BST ceramics with applied DC field is demonstrated in a prototype small resonant antenna.
rate research
Read More
Titanium diboride (TiB2) is a low-density refractory material belonging to the family of ultra-high temperature ceramics (UHTCs). This paper reports on the production and microstructural and optical characterization of nearly fully dense TiB2, with particular interest to its potential utilization as novel thermal solar absorber. Monolithic bulk samples are produced starting from elemental reactants by a two-step method consisting of the Self-propagating High-temperature Synthesis (SHS) followed by the Spark Plasma Sintering (SPS) of the resulting powders. The surface of obtained samples has-been characterized from the microstructural and topological points of view. The hemispherical reflectance spectrum has been measured from 0.3 to 15 um wavelength, to evaluate the potential of this material as solar absorber for future concentrating solar plants.
Conductive and electrostatic atomic force microscopy (cAFM and EFM) are used to investigate the electric conduction at nominally neutral domain walls in hexagonal manganites. The EFM measurements reveal a propensity of mobile charge carriers to accumulate at the nominally neutral domain walls in ErMnO3, which is corroborated by cAFM scans showing locally enhanced d.c. conductance. Our findings are explained based on established segregation enthalpy profiles for oxygen vacancies and interstitials, providing a microscopic model for previous, seemingly disconnected observations ranging from insulating to conducting domain wall behavior. In addition, we observe variations in conductance between different nominally neutral walls that we attribute to deviations from the ideal charge-neutral structure within the bulk, leading to a superposition of extrinsic and intrinsic contributions. Our study clarifies the complex transport properties at nominally neutral domain walls in hexagonal manganites and establishes new possibilities for tuning their electronic response based on oxidation conditions, opening the door for domain-wall based sensor technology.
Whereas low-temperature ferroelectrics have a well understood ordered spatial dipole arrangement, the fate of these dipoles in paraelectric phases remains poorly understood. This is studied here as an energy minimization problem using both static and molecular dynamic (MD) density functional theory (DFT). We find that considering the non-thermal internal energy already reveals the formation of a distribution of static local displacements that (i) mimic the symmetries of the low temperature phases, while (ii) being the precursors of what high temperature DFT MD finds as thermal motifs.
Here we report the development of high-efficiency microscale GaAs laser power converters, and their successful transfer printing onto silicon substrates, presenting a unique, high power, low-cost and integrated power supply solution for implantable electronics, autonomous systems and internet of things applications. We present 300 {mu}m diameter single-junction GaAs laser power converters and successfully demonstrate the transfer printing of these devices to silicon using a PDMS stamp, achieving optical power conversion efficiencies of 48% and 49% under 35 and 71 W/cm2 808 nm laser illumination respectively. The transferred devices are coated with ITO to increase current spreading and are shown to be capable of handling very high short-circuit current densities up to 70 A/cm2 under 141 W/cm2 illumination intensity (~1400 Suns), while their open circuit voltage reaches 1235 mV, exceeding the values of pre-transfer devices indicating the presence of photon-recycling. These optical power sources could deliver Watts of power to sensors and systems in locations where wired power is not an option, while using a massively parallel, scalable, and low-cost fabrication method for the integration of dissimilar materials and devices.
YBCO fabrics composed of nanowires, produced by solution blow spinning (SBS) are so brittle that the Lorentz force produced by induced currents can be strong enough to damage them. On the other hand, it is known that silver addition improves the mechanical and flux pinning properties of ceramic superconductors. Thus, in this work, we show how we successfully obtained a polymeric precursor solution containing YBCO$+$Ag salts, which can be spun by the SBS route to produce ceramic samples. Yttrium, barium, copper, and silver metal acetates, and polyvinylpyrrolidone (PVP) (in a ratio of 5:1wt [PVP:acetates]) were dissolved in a solution with 61.5 wt% of methanol, 12 wt% of propionic acid, and 26.5 wt% of ammonium hydroxide, together with 6 wt% of PVP in solution. Three different amounts of silver (10 wt%, 20 wt%, and 30 wt%) were used in YBa$_2$Cu$_3$O$_{7-x}$. The TGA characterizations revealed a lowering of crystallization and partial melting temperatures by about SI{30}{celsius}. SEM images show that after burning out the polymer, a fabric composed of nanowires of diameters up to SI{380}{ ano metre} is produced. However, after the sintering process at SI{925}{celsius} for SI{1}{hour}, the nanowires shrink into a porous-like sample.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
