Correlation of Chemical Bonding and Optical Phonon Damping with the Dielectric/Thermal Properties of Silicate Microwave Ceramics for S-Band Antenna Applications.

Understanding the intrinsic origins of dielectric loss and thermal transport in microwave dielectric ceramics remains a fundamental challenge for the development of multifunctional materials. Here, LiReSiO4 (Re = Lu, Er, Y) ceramics are synthesized and investigated to elucidate how optical phonon damping and chemical bonding are correlated with dielectric loss and lattice thermal conductivity. The crystal orbital Hamiltonian population (COHP) and infrared absorption spectra from first-principles calculations reveal that stronger optical phonon damping enhances anharmonic phonon scattering, leading to higher dielectric loss. For thermal transport, stronger Re-O bonding enhances phonon group velocity, while optical phonon damping is closely associated with the phonon-scattering behavior relevant to thermal conductivity. Owing to suppressed phonon damping and strong Lu-O bonding, LiLuSiO4 (LLS) achieves a high quality factor (Q × f = 83,689 GHz) and a relatively high thermal conductivity (3.5 W/mK), while maintaining a low permittivity (εr = 8.59) and a near-zero temperature coefficient of resonance frequency (TCF = -7.8 ppm/°C). Excellent dielectric properties are further observed in the terahertz band. An S-band patch antenna based on LLS achieves a 6.17 dBi gain and 96.55% radiation efficiency, while thermal simulations confirm superior heat dissipation. This work links optical phonon damping and chemical bonding to dielectric and thermal properties, thereby offering guidance for the design of multifunctional microwave dielectric ceramics and highlighting the considerable application potential of LLS in advanced wireless communication systems.