Microwave Dielectric and Mechanical Property of Cordierite Ceramics by Ca²⁺ Doping

A series of Ca²⁺-doped cordierite ((Mg_1–xCa_x)₂Al₄Si₅O₁₈) ceramic powders were prepared by a sol–gel method. The effect of the substitution of Ca²⁺ for Mg²⁺ of cordierite ceramics on the sintering properties, structural characteristics, microwave dielectric properties and fracture toughness was investigated. The results show that the introduction of Ca²⁺ can improve the sintering activity of the powder, thus improving the density of the sample and the sintering densification. The single α-cordierite phase is obtained in the range of 0<x≤0.1 because Ca²⁺ is doped into the cordierite structure to form the solid solution. When the x value is larger than 0.1, an anorthite phase appears. The dielectric constant of cordierite ceramic decreases, and the quality factor, the temperature coefficient of frequency and fracture toughness improve when Mg²⁺ substitutes for Ca²⁺. The optimum performance of (Mg_1–xCa_x)₂Al₄Si₅O₁₈ ceramic is obtained when the x value is 0.1, i.e., the dielectric constant of 4.61, the quality factor of 9949GHz and the temperature coefficient of frequency of –26×10^–6/℃, and the fracture toughness of 4.76MPa·m^1/2.