Novel high-entropy microwave dielectric ceramics Sr(La0.2Nd0.2Sm0.2Eu0.2Gd0.2)AlO4 with excellent temperature stability and mechanical properties

Novel high-entropy Sr(La0.2Nd0.2Sm0.2Eu0.2Gd0.2)AlO4 ceramics with a layered perovskite structure have been prepared via the standard solid-state reaction method. The design of high-entropy improves the bond valence and subsequently optimizes the large negative temperature coefficient of resonant frequency (τf = −32 ppm/°C) of the simple SrLaAlO4 ceramics. Excellent temperature stability (τf = −6 ppm/°C) together with a relative permittivity (εr) of 18.6 and a quality factor (Qf = 14,509 GHz) are obtained in Sr(La0.2Nd0.2Sm0.2Eu0.2Gd0.2)AlO4 ceramics sintered at 1475 °C. It indicates that the present ceramics have great application prospects in passive microwave components such as resonators and filters. Meanwhile, significant improvements in compressive strength and strain are achieved, which are 1040 MPa and 15.7% for Sr(La0.2Nd0.2Sm0.2Eu0.2Gd0.2)AlO4 compared to 583 MPa and 12% in SrLaAlO4. The enhanced mechanical properties originate from the dislocation strengthening mechanism as the intertwining of interlayer lattices is revealed from the high-resolution transmission electronic micrographs.