Phase composition, microstructure, and microwave dielectric properties of non-stoichiometric yttrium aluminum garnet ceramics

A series of Y3+xAl5O12 (-0.12 <= x <= 0.12) ceramics were prepared via a solid-state reaction under a vacuum sintering environment to investigate the impact of variations in different cation composition on the phase composition, microstructure, and microwave dielectric properties of yttrium aluminum garnet (Y3Al5O12; YAG) ceramics. X-ray diffraction analyses revealed that Al2O3 precipitates in the Al-excess samples. In contrast, the YAlO3 secondary phase appeared in the Y-excess samples, and variations in the content of both contributed to an increase in lattice parameters. The Rietveld refinement results showed that the lattice parameters and unit cell volume increased as the vertical bar x vertical bar value increased. The secondary phases of granular Al2O3 and YAlO3 crystallized at the extended grain boundaries in samples with excess Al and Y were visible in the scanning electron microscopy images. The electron diffraction patterns confirmed that a small amount of Y2O3 promoted continuous phase boundaries and facilitated the release of internal stresses. Ultimately, after sintering at 1750 degrees C for 12 h and at x = 0.03, the microwave dielectric properties of the non-stoichiometric YAG ceramic sample were epsilon(r) = 11.18, Q x f = 236936 GHz, and tau(f) = -35.9 ppm/degrees C.