Structure and microwave dielectric property relations in (Ba1−xSrx)5Nb4O15 system

The effects of strontium substitution for barium on the structure and microwave dielectric properties of Ba5Nb4O15 compounds is investigated using X-ray diffraction, Raman spectroscopy, and microwave dielectric properties measurement. The symmetric stretching vibration of Ba-rich compounds splits into two narrow Raman-active modes and indicates the existence of a strong anharmonic lattice. Nevertheless, the symmetry changes from P 3 ¯ m 1 to P 3 ¯ c 1 for the Sr-rich compounds. The relative permittivity (ɛr) and temperature coefficient of resonant frequency (τf) increases linearly with an increase of strontium content in Ba-rich compounds, but decreases in Sr-rich compounds. The transition of symmetry influences the variation of ɛr and τf. The behavior of ɛr and τf can also be correlated to the variation of symmetric stretching vibrations of NbO6 octahedra and (c/a) ratio of lattice parameter in the unit cell.