Intrinsic correlation between structure, vibration spectrum and microwave dielectric properties of ferroelectric-dielectric composite ceramics

A novel series of (1-x)Ba0.45Sr0.55TiO3-xMgGa2O4 (x = 0, 10, 30, 50, 70 wt%) ceramics was prepared by a solid-state method to investigate the relationship between their dielectric properties and ion diffusion, composition effect, and lattice vibration. XRD refinement and DFT calculations of Ba0.45Sr0.55TiO3 (BST45) revealed that the substitution of Ga3+ and Mg2+, both of which have small polarizability for Ti4+, reached the saturation state at x = 10 wt%, thus decreasing the quality factor (Q value). In contrast, the addition of MgGa2O4 (MG) with x > 10 wt% significantly reduced the relative permittivity and improved the Q value owing to the compositional effect. The vibration spectra (Raman and FT-IR) confirmed that the Q value initially decreased owing to ion diffusion at x < 10 wt% and then increased with increasing MG content according to the composition effect. Therefore, the Q value was remarkably improved in the Ba0.45Sr0.55TiO3-MgGa2O4 composites, with good tunability and low relative permittivity.