Crystal structure, lattice vibration and microwave dielectric properties of 3CaO•2SiO2•xCaF2 (0 ≤ x ≤ 1.5) ceramics

The crystal structure, lattice vibration and microwave dielectric properties of 3CaO center dot 2SiO(2)center dot xCaF(2) ceramics were investigated in this work. With the increasing of x value, the crystal structure of 3CaO center dot 2SiO(2)center dot xCaF(2) ceramics transfers from rankinite (Ca3Si2O7) to cuspidine (Ca4Si2O7F2). The increase of the vibration energy and shrinkage of [SiO4] tetrahedral unit hampers the ionic polarization and thus reduces relative permittivity (epsilon(r)). The enlarged FWHM of the Si-O stretching peak reflects a more drastic anharmonic lattice vibration, resulting in a lower quality factor (Q x f value). The Raman shift of O/F-Ca-O/F bending peak is positively correlated with the temperature coefficient of resonant frequency (tau(f)). The microwave dielectric properties of epsilon(r) and Q x f value (-@11 GHz) ranging from 7.89 to 8.42, and 21805-46098 GHz, respectively. The stable complex permittivity (epsilon(center dot)(r)) in the frequency range of 20-110 GHz indicates that the fluoride cuspidine ceramics could be a promising candidate for microwave device applications.