Phase transition, infrared spectra, and microwave dielectric properties of temperature-stable CaSnSi1-xGexO5 ceramics

Abstract

The CaSnSi1-xGexO5 (0 ≤ x ≤ 1.0) microwave dielectric ceramics were prepared using traditional solid reaction sintered at 1450 °C-1500 °C for 5 h, and the substitution of Ge4+ for Si4+ formed the CaSnSi1-xGexO5 solid solution at 0 ≤ x ≤ 1.0. The phase transition from monoclinic with A2/a space group to triclinic with A1‾ space group at CaSnSi1-xGexO5 ceramics was clarified by Rietveld refinement and high-resolution transmission electron microscopy/selected area diffraction. The crystal structure, X-ray diffraction patterns, and microwave dielectric properties (εr = 11.28, Q × f = 72,900 GHz at 11.62 GHz, and τf = −62.9 ppm/°C) of novel single-phase CaSnGeO5 ceramic were initially reported. In single-phase area, the increase in SnO6 octahedral distortion could reduce the τf value of CaSnSi1-xGexO5 ceramics (0 ≤ x ≤ 0.6) to near zero. In multiphase area, the near-zero τf value (τf = +5.2 ppm/°C) was obtained at x = 0.7. The remarkable change between +5.2 ppm/°C (x = 0.7) and −77.8 ppm/°C (x = 0.8) of τf value was attributed to the appearance of εr anomaly peak (T1 = 125 °C). The optimal microwave dielectric properties (εr = 11.70, Q × f = 37,900 GHz at 12.6 GHz, and τf = +5.2 ppm/°C) of CaSnSi1-xGexO5 ceramics were obtained at x = 0.7.