KTa_(0.65)Nb_(0.35)O_3 thin films epitaxially grown by pulsed laser deposition on metallic and oxide epitaxial electrodes

摘要

Ferroelectric KTa_(0.65)Nb_(0.35)O_3 (KTN) thin films were grown by pulsed laser deposition on Pt and LaNiO_3 epitaxial electrodes, on (100) and (110) SrTiO3 substrates. The effect of the nature of the electrode on structural and microstructural quality of KTN films was investigated. While epitaxial KTN thin films were successfully obtained on both electrodes, two orientations compete on Pt, whatever the main orientation of Pt is (100) or (110). On LaNiO_3 in contrast, pure (10 0) and (11 0) oriented KTN films were achieved with a high crystalline quality illustrated by narrow co-scans (Δω = 0.56° and AΔω = 0.80° for (1 00) and (110) KTN, to be compared to 0.048° and 0.22° for (1 0 0) and (110) LaNiO_3, respectively). Electrical measurements performed in tunneling atomic force microscopy (TUNA mode) on a KTN/Pt heterostructure showed a high asymmetry of the conduction mechanisms when a positive or a negative bias is applied on the sample. In particular leakage currents appear even at very low positive applied voltage. TUNA imaging operated at a moderate negative applied voltage of -3 V shows that some areas corresponding to grain boundaries seem to be more leaky than others.