Lattice evolution and microwave dielectric properties of La-doped yttrium aluminum garnet ceramics

In this study, Y 3− x La x Al 5 O 12 (0 ≤ x ≤ 0.09) ceramics were synthesized, and the phase composition, lattice evolution, and microwave dielectric properties were investigated in detail. Scanning electron microscopy confirms that the addition of moderate amounts of La 2 O 3 improves the grain development of YAG ceramics, but excessive doping destabilizes the crystal structure. Transmission electron microscopy characterization shows that the variation of the dielectric properties of the samples with x -value is related to the occurrence of benign dislocation structures caused by modifications in the type and content of the A-site rare-earth ions. The variations in relative density, dielectric constant, and quality factor remain basically coordinated. The optimum microwave dielectric properties of La 3+ doped YAG samples are exhibited as ε r = 10.61, Q × f = 187, 542 GHz, τ f = −31.2 ppm/°C when La 2 O 3 is doped at x = 0.015.