Achieving near-zero τf values in Ba5Si8O21-Ba2Si3O8 multi-phase ceramics and their potential applications in LTCC technology

Thermally stable x Ba 5 Si 8 O 21 - (1- x ) Ba 2 Si 3 O 8 and x Ba 5 Si 8 O 21 - (1- x ) Ba 2 Si 3 O 8 - z wt% LiF ceramics were successfully synthesized via a conventional solid-state reaction method. In the x Ba 5 Si 8 O 21 - (1- x ) Ba 2 Si 3 O 8 (0.1 ≤ x  ≤ 0.8) ceramics, only Ba 5 Si 8 O 21 and Ba 2 Si 3 O 8 phases coexisted, with their phase contents confirmed by the Rietveld refinements. The 0.4Ba 5 Si 8 O 21 -0.6Ba 2 Si 3 O 8 ceramic, composed of 40.98 wt% Ba 5 Si 8 O 21 and 59.02 wt% Ba 2 Si 3 O 8 phases, exhibited near-zero τ f and moderate Q × f values. The phase composition controlled the τ f and Q × f values of x Ba 5 Si 8 O 21 - (1- x ) Ba 2 Si 3 O 8 (0.1 ≤ x  ≤ 0.8) ceramics. Moreover, the addition of 3 wt% LiF as a sintering aid reduced the sintering temperature of the 0.4Ba 5 Si 8 O 21 -0.6Ba 2 Si 3 O 8 ceramic to 875 °C, while no other secondary phases were detected in the 0.4Ba 5 Si 8 O 21 -0.6Ba 2 Si 3 O 8 - z wt% LiF ceramics. The 0.4Ba 5 Si 8 O 21 -0.6Ba 2 Si 3 O 8 -3 wt% LiF ceramic demonstrated a dense microstructure and favorable microwave dielectric properties ( ε r = 7.44, Q × f = 8293 GHz and τ f = 2.37 ppm/°C), highlighting its potential for low-temperature co-fired ceramic (LTCC) applications.