I. Vrejoiu, Y.L. Zhu, G. Le Rhun, M.A. Schubert, D. Hesse, M. Alexe
Ferroelectric epitaxial superlattices (SLs) combining tetragonal PbZr0.4Ti0.6O3 and rhombohedral PbZr0.6Ti0.4O3 ultrathin films were grown by pulsed laser deposition onto vicinal SrTiO3 (100) substrates. The thickness of the individual layers was found to play an important role in the overall structure adopted by the superlattices. Below a certain critical bilayer thickness of about 8 nm, the superlattices involve continuous 90° a-c domains, indicating a uniform tetragonal structure.
Fig. 1: TEM cross section micrographs of (a) a [PZT 40/60 / PZT 60/40]10 SL and (b) a [PZT 40/60 / PZT 60/40]22 SL, both of about 170 nm overall thickness.
Fig. 2: Macroscopic hysteresis loops of the two superlattices shown in Fig. 1: Polarization hysteresis loops (a) and (b) correspond to the samples of Fig. 1(a) and (b), respectively. Solid symbols corresond to switching current curves.
For details, see Applied Physics Letters 90 (2007) 072909.