High Qf and near-zero τf of SrLa2Al2O7-based microwave dielectric ceramics modified by interlayer polarization

The microwave dielectric properties of SrLa₂Al₂O₇ ceramic, specifically the quality factor ( Qf ) and temperature coefficient of resonant frequency ( τ f ), were enhanced through substituting La 3+ with Sr 2+ at the A-site and Al 3+ with Ti 4+ at the B-site. Pure-phase Sr/Ti co-substituted Sr 1+2 x La 2−2 x Al 2−2 x Ti 2 x O 7 ceramics were synthesized via solid-phase reaction route. Remarkably, at an optimal substitution level of x  = 0.55, the resulting Sr 2.1 La 0.9 Al 0.9 Ti 1.1 O 7 ceramic exhibited superior microwave dielectric properties: ε r = 25.94 ± 0.32, Qf = 117,300 ± 5700 GHz ( f 0 = 6.40 GHz), τ f = 3.28 ± 0.17 ppm/°C. The increase of Qf value was highly associated with the low interlayer polarization effect caused by the small absolute value of interlayer polarization charges. The τ f value was jointly dominated by both τ ε and the bond valence of B-site bonds.