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

A series of Y 3+x Al 5 O 12 (−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 (Y 3 Al 5 O 12 ; YAG) ceramics. X-ray diffraction analyses revealed that Al 2 O 3 precipitates in the Al-excess samples. In contrast, the YAlO 3 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 | x | value increased. The secondary phases of granular Al 2 O 3 and YAlO 3 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 Y 2 O 3 promoted continuous phase boundaries and facilitated the release of internal stresses. Ultimately, after sintering at 1750 °C for 12 h and at x  = 0.03, the microwave dielectric properties of the non-stoichiometric YAG ceramic sample were ε r = 11.18, Q × f  = 236936 GHz, and τ f  = −35.9 ppm/℃.