Lattice vibrations and dielectric functions of ferroelectric SrBi_(2-x)Nd_xNb_2O_9 bismuth layer-structured ceramics determined by infrared reflectance spectra

摘要

Infrared optical properties of SrBi_(2_x)Nd_xNb_2O_9 (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 NbO_6 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(ε) is estimated to about 4.0 in the high-frequency transparent region.