Lattice vibrations and dielectric functions of ferroelectric SrBi2−xNdxNb2O9 bismuth layer-structured ceramics determined by infrared reflectance spectra

Infrared optical properties of SrBi2−xNdxNb2O9 (SBNN) ceramics with different Nd compositions (from 0 to 0.2) have been investigated by near-normal incident reflectance technique. The experimental spectra in the wavenumbers range of 350–1500 cm−1 were analyzed using the Lorentz oscillator model for five infrared-active phonon mode observed. It is found that the frequencies of the NbO6 tilting and symmetric stretching modes linearly decrease with the Nd composition due to the octahedra distortion. The high-frequency dielectric constant varies in the range from 4.55 ± 0.04 to 4.80 ± 0.04. Owing to the contribution from the stronger electronic transitions, the real part of dielectric function Re(ɛ) is estimated to about 4.0 in the high-frequency transparent region.