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

Abstract

The crystal structure, lattice vibration and microwave dielectric properties of 3CaO·2SiO2·xCaF2 ceramics were investigated in this work. With the increasing of x value, the crystal structure of 3CaO·2SiO2·xCaF2 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 (εr). The enlarged FWHM of the Si–O stretching peak reflects a more drastic anharmonic lattice vibration, resulting in a lower quality factor (Q × f value). The Raman shift of O/F–Ca–O/F bending peak is positively correlated with the temperature coefficient of resonant frequency (τf). The microwave dielectric properties of εr and Q × f value (∼@11 GHz) ranging from 7.89 to 8.42, and 21805–46098 GHz, respectively. The stable complex permittivity (εr∗) in the frequency range of 20–110 GHz indicates that the fluoride cuspidine ceramics could be a promising candidate for microwave device applications.