Correlation between vibrational modes of A-site ions and microwave dielectric properties in (1−x) CaTiO3−x (Li0.5Sm0.5)TiO3 ceramics

Abstract

(1-x)CaTiO3-x(Li0.5Sm0.5)TiO3 (0.7 ≤ x ≤ 0.8, CLST) ceramics with an orthorhombic perovskite structure were fabricated by a conventional solid-state reaction method. The effects of composition variation on the microwave dielectric properties were studied in detail. The permittivity (εr) and quality factor (Q × f) value decreased with an increase in the x value, and the temperature coefficient of the resonant frequency (τf) reached nearly zero. Raman and infrared reflection spectroscopy were employed to reveal the relationship between vibrational modes and microwave dielectric properties. The Raman spectra fitted with the Lorentzian model indicated that the dielectric loss deteriorates with an increase in the x value are the result of the lowered A-site cation ordering degree. The harmonic oscillator model was used to fit the infrared reflection spectra, and the obtained complex dielectric response was extrapolated down to the microwave region. The infrared reflection spectra show that the vibrational modes related to A-site cations at lower frequencies (i.e., <150 cm−1) play the most important role in the microwave dielectric properties of CLST ceramics. The optimal microwave dielectric properties were found to be εr = 109.4, Q × f = 4698 GHz, and τf = 1.6 ppm/°C in the sample of 0.22CaTiO3-0.78(Li0.5Sm0.5)TiO3.