Olivine-type A₂BO₄ ceramics possess a low permittivity (ε_r) and low dielectric loss, contributing to a high quality factor (Q×f). However, the large negative temperature coefficient of the resonant frequency (τ_f) restricts their practical applications. In this work, we prepared a series of CaYGa_1−xAl_xO₄ (x = 0–1) ceramics with low ε_r values via solid-state sintering. By controlling the evolution of orthorhombic olivine to the tetragonal perovskite-like structure (K₂NiF₄) and the ordered regulation of the A-site, an ultralow loss (tanδ = 1.38×10⁻⁴, Q×f = 125,530 GHz, and f = 17.3 GHz for x = 0) and a nearly zero temperature coefficient (τ_f = −0.5 ppm/°C for x = 0.9) were achieved. The significant changes in the dielectric properties (ε_r = 8.3–16.2, Q×f = 125,530–50,660 GHz, and τ_f = −50.9 to 2.9 ppm/°C) of these ceramics are primarily influenced by the characteristics of the second phase, ion polarization, ion order and disorder, and the chemical bonds resulting from structural evolution. Furthermore, a cylindrical dielectric resonator antenna (CDRA) was designed using an ultralow-loss CaYGaO₄ ceramic, achieving a high gain (5.36–6.15 dBi) and efficiency (> 90%) in the bandwidth region (5.065–5.747 GHz), thereby enhancing the efficiency and quality of 5G communications. This work advances the development of control strategies for high-performance dielectric ceramics and dielectric resonator antennas in high-frequency communications.

To explore recycling solutions for used lithium-ion batteries (LIBs), a tribocatalytic method is proposed in this paper. When ZnO nanoparticles were used as catalysts, the leaching rates of lithium and cobalt in lithium cobaltate batteries reached 95% and 84%, respectively. In Li–Co–Mn–Ni batteries, the leaching rates of lithium, cobalt, manganese, and nickel were 96.61%, 90.00%, 76.06%, and 61.78%, respectively. In the acid leaching system, the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) of citric acid (CA) were in more appropriate positions, indicating that CA is more prone to redox reactions when rubbed on the surface of zinc oxide. Compared with H₂O, CA is more electrostatically polarized and can participate in more reactions through electron transfer on the ZnO surface. First-principles calculations of the adsorption energies show that the interactions are stronger when CA molecules are located on the lithium cobalt oxide (LCO)(110) surface. The combination of theoretical calculations and experiments verified that the tribocatalytic weak acid leaching process is an effective ion leaching scheme. The free radicals generated during the catalytic process promoted the leaching of metal ions, thus enabling the recycling of cathode materials for lithium-ion batteries. In addition, this method has great potential for the reduction and leaching of ions.

Dielectric ceramics with low permittivity (ε_r), high quality factor (Q×f), and near-zero resonant frequency (τ_f) in the microwave bands are key materials used in fifth/sixth-generation (5G/6G) telecommunication, whileτ_f of most low-ε_r microwave dielectric ceramics is relatively negative. In this work, the first low-ε_r Ga-based ceramic SrGa₁₂O₁₉ with an anomalous positive τ_f was reported, and the causes of the positive τ_f, intrinsic polarization, and loss mechanism were systematically studied. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that the SrGa₁₂O₁₉ ceramic formed a pure hexagonal magnetoplumbite structure with spinel blocks and rock-salt blocks stacked along the crystallographic c-axis. When sintered at 1430 °C, it possessed the optimal microwave dielectric properties of a low ε_r of 14.46, high Q×f of 64,705 GHz, and exceptional positive τ_f of +55.7 ppm/°C, along with a low linear thermal expansion coefficient (α_L) of 11.617 ppm/°C. The large positive deviation between ε_r and ε_r(C–M) of 45.31% resulted from the rattling effect of atoms in the rock-salt block. The unique positive τ_f (+55.7 ppm/°C) was governed by the rattling effect, resulting in a positive τ_αm (the temperature coefficient of ion polarizability) of 8.489 ppm/°C and a large negative temperature coefficient of permittivity (τ_ε) of −132.864 ppm/°C. Phillips–Vechten–Levine (P–V–L) chemical bond theory revealed greater contributions of the spinel block to bond ionicity (f_i, 52.95%), permittivity (ε, 55.15%), bond energy (E, 56.87%), and lattice energy (U, 74.88%) than those of the rock-salt block. The intrinsic dielectric properties were analyzed using infrared (IR) reflectivity spectra. The favorable performance of the SrGa₁₂O₁₉ ceramic indicated that it is a novel τ_f compensator. This selection of compounds with different structural layer combinations provides a new idea for exploring excellent microwave dielectric ceramics.