Crystal structure and microwave dielectric properties of CaTiO3 modified Mg2Al4Si5O18 cordierite ceramics

• Q × f values obviously increased from 39000 GHz to 55490 GHz by CaTiO3 addition.
• Thermal stability was significantly optimized from −32.8 ppm/°C to −21.6 ppm/°C.
• Densification sintering temperatures were obviously decreased by liquid phase sintering.
• Symmetry of [(Si4Al2O18)] hexagonal rings in cordierite has strong correlation with the microwave dielectric properties.

In this work, CaTiO3 modified Mg2Al4Si5O18 (MAS) of (1−x)MAS-xCaTiO3 (0 ≤ x ≤ 0.35) cordierite ceramics were fabricated by traditional solid phase sintering method. The densification sintering temperatures of (1−x)MAS-xCaTiO3 ceramics are effectively lowered from 1460 °C to 1250 °C with increasing addition of CaTiO3. X-ray diffraction spectra show that (1−x)MAS-xCaTiO3 ceramics present cordierite phase as 0 < x ≤ 0.05, and the composite phases of cordierite, perovskite-structured CaTiO3 and monoclinic feldspar phase of CaAl2Si2O8 as 0.10 ≤ x ≤ 0.35. Rietveld refinement of XRD data show the six-membered rings of [(Si4Al2)O18] transit from non-symmetry rings to centro-symmetry equilateral rings in (1−x)MAS-xCaTiO3 (0 < x ≤ 0.10). The optimal dielectric properties of Q × f = 55490 GHz (at 15.3 GHz), εr = 7.2 and τf = −28.3 ppm/°C are obtained at x = 0.5, which are better than those of pure MAS cordierite ceramics.