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Abstract Yttrium iron garnet and calcium titanate (Y 3 Fe 5 O 12 -CaTiO 3 , 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 CaTi 0.6 Fe 0.4 O 2.8 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. Highlights • Composites demonstrate ferrimagnetic behavior due to Y 3 Fe 5 O 12 phase. • Y 3 Fe 5 O 12 –CaTiO 3 composite can be used as Class 1 ceramic capacitors due to its high thermal-stability. • Resonators can be used in C-band applications: satellite communication, Wi-Fi devices and weather radar systems. [ABSTRACT FROM AUTHOR]

The Sr 3 MoO 6 (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. [ABSTRACT FROM AUTHOR]

Ni 0.5 Zn 0.5 Fe 2 O 4 nanocrystals were successfully synthesized under different pure hydrothermal conditions (no organic solvent). The effects of the NaOH content and reaction time on the growth mechanism, as well as structural, morphological and magnetic properties were investigated. High-resolution electron microscopy transmission (HRTEM) revealed the formation of the nanocrystals, mainly via oriented attachment or in addition by a coalescence mechanism depending on the NaOH concentration (3.7–5.2 M). This secondary mechanism was found to give rise to defects in the network and structural disorder on the surface of the nanocrystals. By extending the reaction time (6–24 h), a morphology transition from truncated-hexagonal to rounded structures was seen, which evidenced a self-integration mechanism to achieve the most stable shape. Moreover, preferential exposure of the (111) plane was observed. Electrochemical measurements using [Fe(CN) 6 ] 3─/4─ to check the surface status further supported this statement. This indicated an adsorption effect of the NaOH on the surface of the MNPs allowing an oriented growth of the nanocrystals. In addition, the blocking temperature ( T B ) was affected by different factors (rearrangement of the atoms on the surface or increase of the magnetically-ordered core) depending on the hydrothermal conditions used. [ABSTRACT FROM AUTHOR]

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 ( ε r ) while YIG is ferromagnetic, has low ε 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 Mössbauer 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. [ABSTRACT FROM AUTHOR]