Boron substitution in LiAlO 2 to facilitate densification and tune dielectric properties

A series of low-permittivity LiAl 1 − x B x O 2 (0.01 ≤ x ≤ 0.10) ceramics were fabricated by a conventional solid-state reaction method and were characterized for their phase evolution, crystal structure, and dielectric properties. Single-phase LiAl 1 − x B x O 2 solid solutions were formed at a limited compositional range ( x = 0.05) while the secondary phase Li 2 (BAlO 4 ) companied at higher dopant contents. Boron substitution facilitated the sintering behavior and optimized the densification of LiAlO 2 , resulting in dense microstructures and improved dielectric properties. A composition with x = 0.075 exhibited a high quality factor ( Q×f ) of 40,288 GHz along with a low relative permittivity ( ε r ) of 6.3 and a temperature coefficient of resonance frequency (τ f ) of – 191 ppm/ o C. All results indicate that the LiAl 1 − x B x O 2 ceramics can be a promising candidate material in the application of the substrate.