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

In this study, Y3-xLaxAl5O12 (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 La2O3 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 La3+ doped YAG samples are exhibited as epsilon(r) = 10.61, Q x f = 187, 542 GHz, tau(f) = -31.2 ppm/degrees C when La2O3 is doped at x = 0.015.