Investigations on KTN thin films by XRD, XPS and micro raman spectroscopy

Abstract

The renewed interest in KTa_1−xNb_xO (KTN) mixed perovskite materials, especially in thin films of a high quality, is connected with their remarkable dielectric properties in the dilute compositions. Off-center Nb ions in the highly polarizable KTaO₃ lattice provide a drastic increase in the dielectric peak up to 20 times in comparison with pure KTaO₃ and KNbO₃. This paper reports a continuation of KTN thin films studies with several Nb concentrations in the range of 0 ≤ x ≤ 1 prepared by pulsed laser deposition from segmented KTaO₃, KNbO₃ and KNO₃ targets. The effect of the substrate and symmetry-breaking defects was studied by micro-Raman spectroscopy. An anomalous residual intensity of the forbidden first-order scattering modes in the cubic paraelectric phase of the KTN films was connected with the formation of polar microregions even far above the bulk T_c value. On the whole, the KTN film behavior shows the existence of specific defects enlarging the perovskite unit cell in the film so that the activity of off-center Nb ions increases in producing larger electric dipoles and extending the precursor phase above T_c.