Interlocking layered Li₂Si₂O₅: A novel low-permittivity microwave dielectric ceramic with superior dielectric and mechanical properties

Achieving low relative permittivity (ε_r) together with high mechanical reliability remains a key challenge for low-temperature co-fired ceramic (LTCC) substrates used in high-frequency communication and electronic packaging. Herein, single-phase Li₂Si₂O₅ ceramics with a stable crystal framework and an interlocked layered microstructure are developed as low-permittivity LTCC substrate candidates. Their microwave and terahertz dielectric properties and mechanical performance are systematically investigated for the first time. The Li₂Si₂O₅ ceramic sintered at 960 ℃ exhibits a low ε_r (4.86 ± 0.01), high quality factor (Q×f = 105,420 ± 366 GHz at 19.5 GHz and 175,131 GHz at 1 THz), and a moderate temperature coefficient of resonant frequency (τ_f = −24.84 ± 1.0 ppm/℃). Meanwhile, it achieves a hardness of 8.34 ± 0.05 GPa, a flexural strength of 320.72 ± 5.0 MPa, and a fracture toughness of 2.49 ± 0.06 MPa·m^1/2, demonstrating its robust mechanical reliability. Furthermore, based on the P-V-L theory, the structure–property relationship between chemical bonding parameters and dielectric response is established. The ionicity of Li-O bonds is found to primarily govern ε_r, whereas the covalent character of Si-O bonds plays a dominant role in reducing intrinsic dielectric loss and regulating temperature stability, providing a theoretical basis for performance optimization. To further assess practical applicability, a 2.45 GHz microstrip patch antenna is designed using Li₂Si₂O₅ +1 wt% LiF ceramic as the substrate. The simulated antenna possesses a high radiation efficiency of 90.64%, a gain of 5.60 dBi, and good impedance matching. These results confirm that Li₂Si₂O₅ ceramics offer a promising combination of low ε_r, low loss, and mechanical robustness for high-frequency electronic packaging and Internet of Things (IoT) devices.