Phase composition and microwave dielectric properties of SrTiO3 modified Mg2Al4Si5O18 cordierite ceramics

The effects of SrTiO3 addition on phase composition and microwave dielectric properties of cordierite (Mg2Al4Si5O18) ceramics had been investigated in this paper. X-ray diffraction data showed that (1 − x)Mg2Al4Si5O18-xSrTiO3|(1 − x)MAS − xST (0 ⩽ x ⩽ 0.35)| ceramics presented β-cordierite solid solution within 0 < x ⩽ 0.10. In the range of 0.15 ⩽ x ⩽ 0.35, the perovskite-structured SrTiO3 and monoclinic phase of SrAl2Si2O8 feldspar were detected. Rietveld refinement of XRD data showed the shapes of [(Si4Al2)O18] hexagonal rings in (1 − x)MAS-xST (0 < x ⩽ 0.10) happened to adjust from non-symmetry rings to centro-symmetry equilateral rings, along with the solution of SrTiO3 into cordierite. The densification sintering temperatures of (1 − x)MAS-xST ceramics were effectively lowered as to the effect of SrAl2Si2O8 feldspar acting as liquid sintering aids, accompanying the improvement of microstructure of (1 − x)MAS-xST (0 ⩽ x ⩽ 0.35) ceramics. Finally, the (1 − x)MAS-xST (x = 0.10) ceramics possessed the best optimal Qf value: εr = 6.53, Qf = 80,600 GHz (fo = 13.6 GHz), τf = −18 ppm/°C. The (1 − x)MAS-xST (x = 0.20) ceramics achieved a relative stable temperature coefficient of resonant frequency with: εr = 6.01, Qf = 51,800 GHz (fo = 13.1 GHz), τf = −11 ppm/°C.