SrGa ₁₂O ₁₉: The first low- ε r Ga-based microwave dielectric ceramic with anomalous positive τ f

Dielectric ceramics with low εr, high Q×f, and near-zero τf in the microwave bands are key materials used in fifth/sixth-generation (5G/6G) telecommunication, while the τf of most low-εr microwave dielectric ceramics is relatively negative. In this work, the first low-εr Ga-based ceramic SrGa₁₂O₁₉ with anomalous positive τf was reported, and the cause of positive τf, intrinsic polarization and loss mechanism were systematically studied. According to XRD and TEM, SrGa₁₂O₁₉ ceramic formed a pure hexagonal magnetoplumbite structure with the spinel block and the rock-salt block stacking along the crystallographic c-axis. When sintered at 1430 °C, it possessed the optimal microwave dielectric properties of low εr of 14.46, high Q×f of 64,705 GHz, and exceptional positive τf of +55.7 ppm/°C, along with a low linear thermal expansion coefficient (αL) of 11.617 ppm/°C. The large positive deviation between εr and εr(C-M) of 45.31% resulted from the rattling effect of atoms in a rock-salt block. The unique positive τf (+55.7 ppm/°C) was governed by the rattling effect, resulting in a positive ταm of 8.489 ppm/℃ and a large negative τε of −132.864 ppm/℃. The P-V-L chemical bond theory showed the greater contribution of the spinel block to fi (52.95%), ε (55.15%), E (56.87%) and U (74.88%) than those of the rock-salt block. The intrinsic dielectric properties were analyzed using infrared reflectivity spectra. The favorable performances of SrGa₁₂O₁₉ ceramic indicated it is a novel τf compensator. This selection of compounds with different structural layer combinations provides a new idea for exploring excellent microwave dielectric ceramics.