Possible absence of critical thickness and size effect in ultrathin perovskite ferroelectric films.

ABSTRACT: Although the size effect in ferroelectric thin films has been known for long time, the underlying mechanism is not yet fully understood and whether or not there is a critical thickness below which the ferroelectricity vanishes is still under debate. Here, we directly measure the thickness-dependent polarization in ultrathin PbZr_0.2Ti_0.8O₃ films via quantitative annular bright field imaging. We find that the polarization is significantly suppressed for films <10-unit cells thick (?4?nm). However, approximately the polarization never vanishes. The residual polarization is ?16??Ccm^-2 (?17%) at 1.5-unit cells (?0.6?nm) thick film on bare SrTiO₃ and ?22??Ccm^-2 at 2-unit cells thick film on SrTiO₃ with SrRuO₃ electrode. The residual polarization in these ultrathin films is mainly attributed to the robust covalent Pb-O bond. Our atomic study provides new insights into mechanistic understanding of nanoscale ferroelectricity and the size effects.

SUBMITTER: Gao P 

PROVIDER: S-EPMC5467161 | biostudies-literature | 2017 Jun

REPOSITORIES: biostudies-literature