Symmetry consideration of Raman modes in Nd-doped lead zirconate titanate thin films for structure characterization

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Abstract
A short group‐theoretical discussion is given of phonon symmetries in different phases of the Pb(ZrxTi1−x)O3 (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 the consideration of Raman modes, measured from Nd‐doped PZT thin films with Zr concentrations below or near to the morphotropic phase boundary between the ferroelectric tetragonal and trigonal phases. Raman spectroscopy was used in addition to x‐ray diffraction experiments for the characterization of the phase structure in the films. Raman spectra were measured at room temperature and also at some higher temperatures up to 318 °C. A XeCl‐excimer laser was used for the pulsed laser ablation of thin films from a Pb0.97Nd0.02(Zr0.55Ti0.45)O3 target on sapphire and MgO substrates without substrate heating. After ablation, the amorphous films were annealed at temperatures between 700 and 900 °C. Energy dispersive spectroscopy of x rays was used for the composition analysis of the films. Different film compositions were obtained by using different laser‐beam fluences during the ablation process. The Zr/(Zr+Ti) ratio in the films varied between 0.32 and 0.50.