Uniform orientation and size of ferroelectric domains

Abstract

Rochelle salt (RS) $(\mathrm{Na}\mathrm{K}{\mathrm{C}}_{4}{\mathrm{H}}_{4}{\mathrm{O}}_{6}∙4{\mathrm{H}}_{2}\mathrm{O})$ single crystals were grown inside an array of alumina pores having an average diameter of $30\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and length of about $0.5\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$. The crystals have a monoclinic crystallographic structure and uniform crystallographic orientation. High-resolution transmission electron microscopy vertical cross section images show multiple nanometer-sized 180\ifmmode^\circ\else\textdegree\fi{} ferroelectric domains in each single crystal having uniform size and orientation along the longitudinal axis of the pores. The nanodomain boundaries consist of a single crystallographic plane of a rotation twin. This configuration of ferroelectric nanodomains results in enhanced polarization, which is higher by one order of magnitude than the maximum polarization values reported for bulk-size RS crystals. The pores stabilize the ferroelectric phase up to $55\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ (decomposition temperature of RS), which is higher by about $30\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ relative to the upper transition temperature of bulk-size RS crystals. The highly dense array of individual ferroelectric single crystals with uniform polarization orientation and size of nanodomains, as presented in this paper, is a basis for future high-resolution and high-density ferroelectric-based devices, where each nanocrystal inside a pore can serve as a detector, sensor, or actuator.