Abstract
The PbTiO3/SrTiO3 superlattice thin films with a low volume fraction of PbTiO3 have not attracted much interest because they are thought to exhibit only a paraelectric state. In this study, we focus on a superlattice thin film with thin PbTiO3 (PTO) and thick SrTiO3 (STO) layers, wherein the hidden ferroelectricity in the thin PbTiO3 layer is revealed. Atomic scale imaging analysis and electron energy loss spectroscopy reveal the existence of a disordered ferroelectric polarization state without innate tetragonal distortion in the (6PTO/15STO)5 superlattice. The piezoelectric force microscopy analysis confirms that this disordered ferroelectricity can enhance piezoelectric response.
Highlights
Imperfections in the charge screening from polarization at the interfaces create a depolarization field, which is a major obstacle to obtain stable polarization states in ferroelectric thin films
The PbTiO3 (PTO)/SrTiO3 (STO) superlattice grown on a STO substrate is an ideal system to investigate the electrostatic effect because of the excellent in-plane mechanical coupling between
We previously focused on characterizing the local polarization state in the PTO/STO superlattice with 0.3 PTO volume fraction, which is known to be near the paraelectric limit.[18,19,20]
Summary
Polarization stability is a limiting factor for miniaturization of electrical devices used for memory and data storage.[1,2,3] imperfections in the charge screening from polarization at the interfaces create a depolarization field, which is a major obstacle to obtain stable polarization states in ferroelectric thin films. We previously focused on characterizing the local polarization state in the PTO/STO superlattice with 0.3 PTO volume fraction, which is known to be near the paraelectric limit.[18,19,20] Here, to eliminate the ferroelectric dimensional effect, we chose a superlattice structure with sixunit-cell-thick PTO layers because it has sufficient thickness to maintain the ferroelectricity.[21,22,23] To observe the polarization states at the atomic scale, we performed a scanning transmission electron microscopy (STEM) study, including the high-angle annular dark field (HAADF) image and electron energy-loss spectrum (EELS) analysis with EELS calculation results.
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