Crystal structure and dielectric properties of (1−x)SrTiO3-xCa0.4Sm0.4TiO3 ceramic system at microwave frequencies

• The (1−x)ST-xCST (0.6 ≤ x ≤ 0.9) ceramics can form a single perovskite phase.
• The variation of Q∙f values has strongly depend on the grain size.
• The τf values with B-site bond valence are discussed by the theory of bond valence.
• The τf values decrease with decreasing tolerance factor (t) in perovskite structure.

(1−x)SrTiO3-xCa0.4Sm0.4TiO3 (0.6 ≤ x ≤ 0.9) ceramics are prepared through the conventional solid-state route. Powders are calcined at 1200 °C and sintered at 1400–1500 °C. High density, CaTiO3-like perovskite structures are obtained in the range 0.6 ≤ x ≤ 0.9. The phase purity, microstructures and microwave dielectric properties are investigated. With an increase of Ca0.4Sm0.4TiO3 content, the dielectric constant (εr) decreases, which is dependent on the difference of ionic polarizability between Ca0.4Sm0.4TiO3 and SrTiO3. The product of dielectric Q value and resonant frequency (Q∙f) increases up to x = 0.8, and then decreases due to the abnormal grain growth. The variation of temperature coefficient of resonant frequency (τf) with B-site bond valence and tolerance factor (t) is discussed by using the theory of bond valence and the changes of tolerance factor in perovskite structure. The (1−x)SrTiO3-xCa0.4Sm0.4TiO3 (0.6 ≤ x ≤ 0.9) ceramics show the dielectric properties of εr ∼ 101.4–142.7, Q∙f ∼ 1999.5–5986.3 GHz (at 2.8–4 GHz) and τf ∼ 359.8–199.6 ppm/°C at different sintering temperatures of 1400–1500 °C for 4 h.

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