Low-dielectric microwave ceramics Ca1-xSrxB2O4 with excellent compatibility with silver

Ca 1- x Sr x B 2 O 4 ( x  = 0–0.5) ceramics are prepared using the conventional solid-state method, and their crystal structure, microstructure, microwave dielectric properties, and low-temperature co-firing characteristics are systematically studied. To enhance the crystalline structure order, this study aims to improve the sintering performance of CaB 2 O 4 by forming a solid solution with Sr 2+ substituting Ca 2+ sites. X-ray diffraction results indicate that with the doping of Sr 2+ , the unit cell volume of Ca 1- x Sr x B 2 O 4 ceramics increases, and the diffraction peaks shift to lower angles. EDS results confirm that Sr 2+ is uniformly distributed in the Ca 1- x Sr x B 2 O 4 ceramics, successfully forming a solid solution. SEM analysis reveals that an appropriate amount of Sr 2+ improves grain uniformity and reduces porosity between grains. Raman spectroscopy shows that moderate Sr 2+ doping enhances the order of the crystalline structure, leading to an increase in the Q × f value of the ceramics. When x  = 0.03 and the sintering temperature is 900 °C, Ca 1- x Sr x B 2 O 4 ceramics exhibit optimal microwave dielectric properties: ε r  = 5.53, Q × f  = 33,135 GHz, τ f  = −27.37 ppm/°C. During co-sintering with Ag electrodes, Ca 1- x Sr x B 2 O 4 ceramics show excellent chemical compatibility with Ag powder, with no silver diffusion observed. This demonstrates the great potential of Ca 1- x Sr x B 2 O 4 ceramics for LTCC applications.