Uniform orientation and size of ferroelectric domains

Rochelle salt (RS) $(\mathrm{Na}\mathrm{K}{\mathrm{C}}_4{\mathrm{H}}_4{\mathrm{O}}_6\bullet 4{\mathrm{H}}_2\mathrm{O})$ single crystals were grown inside an array of alumina pores having an average diameter of $30\mathrm{nm}$ and length of about $0.5\mu \mathrm{m}$. 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° 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 $55°\mathrm{C}$ (decomposition temperature of RS), which is higher by about $30°\mathrm{C}$ 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.