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Ba5Li2W3O15 (BLWO) electroceramics with different amounts of lithium carbonate (10–15%) were synthesized using the solid-state route. Powder x-ray diffraction (PXRD) and Raman spectroscopy showed the presence of the BaWO4 (BWO) phase in the samples. The excess lithium in the BLWO matrices contributed to an increase in the BWO phase and improved the thermal stability. Images obtained by scanning electron microscopy (SEM) showed grains without a well-defined morphology and with a low porosity. The dielectric properties in the microwave (MW) range for the dielectric resonator based on BLWO were analysed by the Hakki–Coleman and Silva–Fernandes–Sombra methods. The near-zero temperature coefficient of resonant frequency (6.59 ppm°C−1) was obtained for the sample synthesized with 15% Li2CO3. Numerical studies based on the coefficient of reflection (S11) and impedance values of the BLWO-based dielectric resonator antennas (DRA) were also conducted. They agreed well with the experimental results, which indicates that this material can be applied as an antenna device in the MW range.

Yttrium iron garnet and calcium titanate (Y3Fe5O12-CaTiO3, YIG-CTO) ceramic composite were obtained according to the well-established solid-state route. This system was studied by complex impedance spectroscopy as a function of temperature. All samples showed a thermo-activated relaxation with energy activation between 1.10 and 1.70 eV. The CaTi0.6Fe0.4O2.8 phase is formed during sintering process, which influences in the electrical behavior of the samples. Nyquist diagrams were adjusted by two equivalent circuits in series to represent electric response. The YIG-CTO system was also used to design a dielectric resonator antenna (DRA) for microwave applications. The results indicate that DRA YIG-CTO-based presented an operation frequency range around 1–7 GHz, and reflection coefficient below −38 dB. From obtained results, the YIG-CTO composite is a great candidate for usage in electronic devices, operating in the C-band, such as WiFi and ISM band applications.

The Sr3MoO6 (SMO) double perovskite has been studied due to its photoluminescence properties. Herein, the aim of this work is to study the dielectric properties of the SMO in radiofrequency (RF). From impedance spectra, we proposed an equivalent circuit using three associations of R-CPE in parallel. We also evaluated its performance as a microwave device (dielectric resonator antenna - DRA). The SMO-based DRA operated at 3.71 GHz (frequency of operation antenna), with reasonable gain (5.00 dBi) and directivity (5.70 dBi), where these values are close to the ones presented by commercial antennas. Additionally, a numerical simulation is performed to obtain the main parameters for proper device application. Based on our results, SMO electroceramic shows important properties, which can be used for devices operating in the S-band such as weather radar, surface ship radar and communications satellites.

Eu3+ – Tb3+ co-doped Sr3MoO6 (SMO) phosphors have been synthesized by solid-state reaction. Powder X-ray diffraction (PXRD) and Scanning electron microscopy (SEM) were used for the characterization of the synthesized materials, and no significant structural changes have been observed. Photoluminescence (PL) was obtained under the 290 nm excitation where a strong energy transfer from host to active ions and weak energy transfer between the active ions with prominent emission from respective active ions. The fluorescence intensity ratio (FIR) was evaluated as a function of temperature in the range of 14 and 300 K using Eu3+/Tb3+ ratio to obtain absolute (SA) and relative (SR) sensitivities. SMO:Eu/Tb presented maximum SA of 0.0029 K−1 at 300 K and SR of 0.24% K−1 at 300 K, demonstrating that investigated system could be used in temperature sensing applications at low temperature.

This work reports the dielectric properties of Sr3WO6 (SWO) double perovskite at radio frequencies as a function of the temperature and a study in microwaves range to evaluate the material as a novel dielectric resonator. Thermo-activated charge transfer process for SWO ceramic was observed and two resistor–capacitor associations were fitted for the Nyquist diagram. SWO presented negative values of temperature coefficient of capacitance (TCC) and the activation energies of dielectric relaxation processes were measured by conductivity (1.35 eV), imaginary modulus (1.38 eV) and imaginary impedance (1.36 eV). For the microwave range, SWO shows high dielectric permittivity (13.57) and dielectric loss (0.0281). The dielectric resonator antenna (DRA) fabricated from SWO ceramic presented an operation frequency in 4.1 GHz and return loss below −40 dB. It was possible to evaluate the performance of the antenna from numerical simulation. From these results, the SWO based DRA shows good properties to be used as a novel microwave dielectric resonator.

This work investigates the microstructure and magnetic–dielectric properties of the CaTiO 3 (CTO) and Y 3 Fe 5 O 12 (YIG) composite ceramic. CTO is a paramagnetic ceramic, presents a positive value of Resonant Frequency Temperature Coefficients ( τ f ) and has high dielectric permittivity ( e r ) while YIG is ferromagnetic, has low e r and negative τ f values. Therefore, it is expected that the composite from these individual phase shows new properties, or a mix of them derived from each component. X-ray powder diffraction (XRPD), Scanning Electron Microscope (SEM), Raman and 57 Fe Mossbauer spectroscopy were performed to confirm the phases of the composites. The dielectric and magnetic properties in Radio-Microwave frequencies were studied by impedance spectroscopy using different geometries. It was observed a densification improvement resulting from the insertion of the CTO in composites and a chemical reaction between YIG and CTO phases. This new composite has potential applications in bulk and thick/thin films devices.