Microwave dielectric properties of silico-carnotite Ca3M2Si3O12 (M= Yb, Y) ceramics synthesized via high energy ball milling

The Ca 3 M 2 Si 3 O 12 (M = Yb, Y) ceramics with orthorhombic silico-carnotite structure were fabricated via high-energy ball milling and solid-state reaction route. Dense Ca 3 Yb 2 Si 3 O 12 and Ca 3 Y 2 Si 3 O 12 ceramics sintered at 1260 °C and 1240 °C revealed promising microwave dielectric properties with ε r  = 9.2 and 8.7, Q×f = 56,400 GHz and 29,094 GHz, τ f  = −77.5 ppm/°C and −76.8 ppm/°C, respectively. The connection between crystal structure and Q×f values of Ca 3 M 2 Si 3 O 12 (M = Yb, Y) ceramics was discussed with respect to the packing fraction, and their intrinsic microwave dielectric properties were examined using the infrared reflectivity spectra analysis. The thermal stability of Ca 3 Yb 2 Si 3 O 12 was improved successfully by forming 0.91Ca 3 Yb 2 Si 3 O 12 ‐0.09CaTiO 3 composite ceramics with τ f  = +2.9 ppm/°C, ε r  = 12.93 and Q×f  = 26,729 GHz.