Dimensional effiects on ferroelectrics: Ultra-thin single crystals, nanotubes, nano-rods, and nano-ribbons.

A discussion is presented of nano-scale ferroelectric devices. Nano-ribbons exhibit an “extra” relaxation process with an 0.20 ± 0.01 eV activation energy attributed to OH hydroxyl ion reorientation. Barium titanate single crystals down to 65-nm are characterized by bulk properties, and broadening of dielectric peaks ε(T) versus temperature attributed by others to intrinsic depolarization effects are instead shown to be extrinsic, due to oxygen vacancy gradients, in accord with the recent models of Catalan et al. and of Bratkovsky and Levanyuk. Similar transitions in barium strontium titanate (BST) thin films are shown to be reentrant (only upon warming from T < 50 K) and limited by kinetics, not thermodynamic equilibria