A novel strategy to assemble core–shell-structured LiF-CaTiO₃ microwave dielectric ceramics via cold sintering and post-annealing treatment

A novel core–shell architecture is proposed and proved to be effective in achieving temperature-stable LiF-CaTiO₃ microwave dielectric ceramics. Dense CaTiO₃ ceramics are initially prepared using the solid-state reaction method and then inserted into the inner core of LiF green pellets. The assembled green pellets are pre-densified using a cold-sintering process (150 °C, 350 MPa, 60 min) and then post-annealed at 800 °C to obtain densified core–shell-structured LiF-xwt%CaTiO₃ ceramics (x = 3, 5, 10, 15). The SEM images confirm the core-shelled microstructure, and the excellent chemical compatibility between LiF and CaTiO₃ components is revealed from the XRD and EDS results. The large negative temperature coefficient of the resonant frequency of LiF ceramics (− 138 ppm/°C) can be effectively tuned to 2.89 ppm/°C at x = 3, together with a Qf value of 26,580 GHz and ε_r = 10.89. Therefore, cold sintering and post-annealing treatments open up new ways in designing and constructing novel microwave dielectric ceramics with high performance and should also be instructive in areas, such as ferroelectrics and energy storage ceramics.