AgLnMo2O8 (Ln = Sm, Yb) scheelite ceramics with low sintering temperatures for LTCC and C-band antenna applications

Two novel microwave dielectric ceramics, AgLnMo 2 O 8 (Ln = Sm, Yb), with low permittivity and sintering temperatures, were successfully obtained through the traditional solid-phase synthesis method. XRD analysis coupled with Rietveld refinement confirmed that the as-obtained sample possesses a single-phase tetragonal scheelite-type crystal structure with space group I 4 1 / a . The superior microwave dielectric responses were secured at 825 °C for AgSmMo 2 O 8 ( ε r  = 11.74, Q × f  = 89,000 GHz, τ f  = −47.44 ppm/°C) and 800 °C for AgYbMo 2 O 8 ( ε r  = 13.29, Q × f  = 73,000 GHz, τ f  = −36.54 ppm/°C). Bond valence and Raman analyses demonstrate that Ag + is locally compressed whereas Ln 3+ is underbonded (rattling) at shared dodecahedral sites. The compressed Ag  +  contributes to the negative τ f values, whereas the smaller Yb 3+ exhibits a more intense rattling effect than Sm 3+ , causing a higher permittivity, elevated loss, and a positive τ f shift. Both ceramics exhibited excellent chemical compatibility with silver-based electrodes, with no new phases observed during co-firing. A cylindrical dielectric resonator antenna was simulated with a resonance frequency of 4.067 GHz and a bandwidth of 289 MHz, using the AgSmMo 2 O 8 ceramic material. The outstanding performance suggests that AgLnMo 2 O 8 (Ln = Sm, Yb) ceramics may be promising candidates for LTCC technologies and C-band antennas.