Group-theoretical consideration of raman modes in Nd-doped PZT thin films for structure characterization

Abstract

Pulsed laser ablation was used to deposit Nd-doped lead zirconate titanate (PZT) thin films from a Pb_0.97Nd_o.o2(Zr_0.55Ti_0.45)O₃ target on sapphire substrates using a XeCl-excimer laser. Energy dispersive spectroscopy (EDS) of x rays was used for the composition analysis of both annealed (between 700°C and 900°C) and unannealed (amorphous) films deposited using various laser-beam fluences. The Zr/(Zr+Ti) ratio varied between 0.32 and 0.50 in the films. A short group-theoretical discussion is given of the phonon symmetries in the different phases of the Pb(ZrxTi1−x)0₃ (PZT) perovskite together with a description of the degeneracy splitting in consequence of the long-range Coulomb fields both in the paraelectric cubic phase and ferroelectric tetragonal and trigonal phases. Phonon symmetries together with the frequency splitting are used for labelling the Raman modes measured from Nd-doped PZT thin films with compositions around the morphotropic phase boundary (MPB). Raman spectroscopy was used in addition to x-ray diffraction experiments for the characterization of the phase structure in the films.