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

The CaSnSi 1- x Ge x O 5 (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 Ge 4+ for Si 4+ formed the CaSnSi 1- x Ge x O 5 solid solution at 0 ≤  x  ≤ 1.0. The phase transition from monoclinic with A 2/ a space group to triclinic with A 1 ‾ $\bar{1}$ space group at CaSnSi 1- x Ge x O 5 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 ( ε r  = 11.28, Q  ×  f  = 72,900 GHz at 11.62 GHz, and τ f  = −62.9 ppm/°C) of novel single-phase CaSnGeO 5 ceramic were initially reported. In single-phase area, the increase in SnO 6 octahedral distortion could reduce the τ f value of CaSnSi 1- x Ge x O 5 ceramics (0 ≤  x  ≤ 0.6) to near zero. In multiphase area, the near-zero τ f value (τ f  = +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 τ f value was attributed to the appearance of ε r anomaly peak (T 1  = 125 °C). The optimal microwave dielectric properties ( ε r  = 11.70, Q  ×  f  = 37,900 GHz at 12.6 GHz, and τ f  = +5.2 ppm/°C) of CaSnSi 1- x Ge x O 5 ceramics were obtained at x  = 0.7.