Synergistic enhancement of thermal conductivity, dielectric properties, and flexural strength in AlN ceramics via Y₂O₃–LiF sintering and annealing

The effects of Y₂O₃–LiF sintering additives on the microstructure, thermal conductivity, flexural strength, and dielectric properties of AlN-based ceramics were systematically investigated. Six different compositions were prepared via ball milling, hot-press sintering, and annealing. XRD and Rietveld refinement confirmed a hexagonal structure for all samples, with changes in the Al–N bond length along the C-axis. SEM analysis revealed that the Y₂O₃–LiF additives modified the morphology of the secondary phase while maintaining a high bulk density. Moreover, annealing resulted in grain boundary purification. As LiF content increased, the second-phase morphology evolved from oval to strip-like, and annealing reduced this phase, improving overall performance. Raman spectroscopy indicated lattice expansion and a blue shift with increasing LiF content. Dielectric analysis of the 2 wt% LiF–Y₂O₃ sample revealed a dielectric constant of 8.56, a dissipation factor of 2.1 × 10⁻⁴, and a high activation energy of 1.38 eV.