Effect of particle size on the optical properties of lead zirconate titanate nanopowders

Nanopowder samples of lead zirconate titanate (Pb1.1Zr0.52Ti0.48O3 or PZT) were prepared by the sol-gel method with controlled pH values. The samples were characterized using FTIR spectroscopy, XRD, FE-SEM, and TEM techniques. Most of the peaks in the XRD pattern were related to the coexistence of tetragonal-rhombohedral phases and confirmed the formation of PZT with a perovskite structure. Also, the crystallite size of PZT nanopowders was in a range of 17-28 nm. FTIR spectroscopy revealed a longitudinal optical (LO) and transverse optical (TO) phonon modes corresponding to the stretching vibration of Ti-O and Zr-O bonds. The influence of pH values on the LO and TO phonon modes, LO-TO splitting, refractive index n(omega), extinction coefficient k(omega), and the real epsilon(1)(omega) and imaginary epsilon(2)(omega) parts of dielectric function was discussed. These properties were investigated in the mid-infrared region (450-750 cm(-1)). The energy loss function Im[-1/(epsilon)] of PZT nanopowders was obtained by Kramers-Kronig dispersion relations. The TO phonon frequency decreases with increasing crystallite size of the PZT samples. This effect does not happen at pH 8 to pH 9. As the crystallite size increased from 17.26 nm (at pH 5) to 27.25 nm (at pH 7), the LO-TO splitting increased as well. This result showed that the optimum pH for absorption of IR radiation and optical application was at pH 7.