RESUMEN
Vanadium(V)-substituted cerium niobate [Ce(Nb1-xVx)O4, CNVx] ceramics were prepared to explore their structure-microwave (MW) property relations and application in C-band dielectric resonator antennas (DRAs). X-ray diffraction and Raman spectroscopy revealed that CNVx (0.0 ≤ x ≤ 0.4) ceramics exhibited a ferroelastic phase transition at a critical content of V (xc = 0.3) from a monoclinic fergusonite structure to a tetragonal scheelite structure (TF-S), which decreased in temperature as a function of x according to thermal expansion analysis. Optimum microwave dielectric performance was obtained for CNV0.3 with permittivity (εr) of â¼16.81, microwave quality factor (Qf) of â¼41â¯300 GHz (at â¼8.7 GHz), and temperature coefficient of the resonant frequency (TCF) of â¼â¯-3.5 ppm/°C. εr is dominated by Ce-O phonon absorption in the microwave band; Qf is mainly determined by the porosity, grain size, and proximity of TF-S; and TCF is controlled by the structural distortions associated with TF-S. Terahertz (THz) (0.20-2.00 THz, εr â¼ 12.52 ± 0.70, and tan δ â¼ 0.39 ± 0.17) and infrared measurements are consistent, demonstrating that CNVx (0.0 ≤ x ≤ 0.4) ceramics are effective in the sub-millimeter as well as MW regime. A cylindrical DRA prototype antenna fabricated from CNV0.3 resonated at 7.02 GHz (|S11| = -28.8 dB), matching simulations, with >90% radiation efficiency and 3.34-5.93 dB gain.
RESUMEN
The efficient electrochemically promoted [3 + 2] annulation of imidazo[1,2-a]pyridines with alkynes using traceless electrons as green reagents has been developed, leading to the synthesis of a large class of polycyclic heteroaromatics in good yields with a broad substrate scope under mild and green conditions. The scaled-up experiment, follow-up procedures, and potential biological applications show the practicability and feasibility of the electrochemical method.
