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In this article, garnet-type Y3Al5O12 (YAG) were doped with Mg2+-Si4+ ionic pairs and its effect on the structure and the microwave dielectric properties was investigated. It was revealed that in ceramics Y3MgxAl5-2xSixO12 (x = 0, 0.5, 1.0, 1.5, 2.0), increasing doping concentration decreased the sintering temperature and time for the optimal densification. X-ray diffraction studies showed that the samples are isostructural to Al5Y3O12 garnet. All sample were formed a single phase except for x = 2.0, where a secondary peak was detected. Excellent microwave dielectric properties of εr = 10.56, Q × f = 67,571 GHz and τf = -35.23 ppm/°C were obtained for Y3Mg0.5Al4Si0.5O12 ceramics sintered at 1625 °C for 5 h. The factors influencing the microwave dielectric properties of Y3MgxAl5-2xSixO12 ceramics were further discussed by considering the ionic polarization, packing fraction, average grain size and chemical bond valence theory. [ABSTRACT FROM AUTHOR]

In this study, MgxY3-xAl5-xSixO12 (x = 0–0.6) ceramics were prepared via a high-temperature solid state method. Mg2+ and Si4+ replacing Y3+ ions at A-site and Al3+ at C-site in garnet-type Y3Al5O12 (YAG) ceramics were designed to discuss the effects of crystal structure, microstructure on microwave dielectric properties for the first time. Liquid phase sintering induced by doping of Mg2+-Si4+, significantly decreased the sintering temperature and time for the densification of YAG ceramics. X-ray diffraction of the samples showed single phase for x ≤ 0.5, while a secondary phase of MgAl2O4 formed for x = 0.6. From the Rietveld analysis, a decrease in lattice dimensions, bond length and valence and rattling effect were observed, while Raman results showed a change in FWHM of the Eg mode. Based on these parameters, a structure–property relation was developed for MgxY3-xAl5-xSixO12 ceramics. Specially, Mg0.1Y2.9Al4.9Si0.1O12 showed a good set of microwave dielectric properties sintered at 1575 °C for 4 h with εr = 10.67, Q × f = 58,799 GHz, τf = -29.5 ppm/°C. [ABSTRACT FROM AUTHOR]

This paper studies the microwave dielectric properties, microstructure, vibration and densification of Li2ZnTi3+xO8+2x (-0.04≤x≤+0.06) ceramics, manufactured via a conventional mixed oxide route. The X-ray diffraction and Raman spectroscopy revealed the unit cell parameter and cation ordering in LZT non-stoichiometry in their vibrational modes. The densification and phase composition were characterized by the EDX and SEM methods. It was found that a slight Ti vacancy can improve the relative density to the maximum value (96.2%). The XRD results showed that the second phase of TiO2 in the Li2ZnTi3.06O8.12 composition is formed. The sintered samples were detected in the microwave frequency range by using the resonance technique. The τf values of the ceramics within Ti excess adjusted to near zero. The Li2ZnTi2.96O7.92 ceramic showed the best relative density, single phase and best microwave dielectric εr=25.98, Q × f = 61,000 GHz, τf=-17.4ppm/∘C sintered at 1100 °C for 4 h. [ABSTRACT FROM AUTHOR]