dr. Jutta Schwarzkopf: Ferroelectric domains in anisotropically strained (KNa)NbO3 thin films grown by MOCVD
|Wanneer:||wo 11-06-2014 16:00 - 17:00|
Formation of ferroelectric domains in thin oxide films have large impact on the ferro- and piezoelectric properties of thin films and can systematically be influenced by the growth of epitaxially strained thin films on lattice mismatched substrates. In this study, thin films of KxNa1-xNbO3, which exhibits promising piezoelectric properties as bulk material, were grown by the liquid-delivery spin metal-organic chemical vapor deposition method. However, less is known about thin films. Understanding and controlling of domain formation is achieved by the variation of the the film composition (x=0-0.9) and the lattice mismatch between film and substrate material. For that purpose we applied DyScO3, TbScO3, NdScO3 and SrTiO3 oxide single-crystals as substrates.
Our results clearly indicate that the alignment of the ferroelectric domains and thus the polarizatioin vector strongly depends on the choice of the substrates. While films under tensile lattice strain exhibit regularly arranged a1a2 domains with an exclusive in-plane alignment of the polarization vector, with increasing compressive lattice strain an enhanced out-of-plane component of the polarization vector develops. We have observed the formation of well-ordered multi-domains and the sequence a1a2→ a1a2/c → MB → MA → MC. Piezoresponse force microscopic measurements on K0.75Na0.25NbO3 thin films on SrTiO3 substrates essentially points to show small, irregular arranged domains with enhanced out-of-plane and in-plane piezoresponse. Decay of the piezorespons signal after poling as a function of time is well described by the Kohlrausch-Williams-Watts (KWW) relaxation function with β ≈ 0.4, which indicates relaxor behavior which we had detected for NaNbO3 films onNdGaO3 substrates .