Layered Perovskites with Giant Spontaneous Polarizations for Nonvolatile Memories

A series of titanate-based layered perovskites having large values of the spontaneous polarization ${P}_{s}$ were developed for their applcations to nonvolatile ferroelectric random access memories. Among these, the Nd-modified bismuth titanate [${\mathrm{B}\mathrm{i}}_{4\ensuremath{-}x}{\mathrm{N}\mathrm{d}}_{x}{\mathrm{T}\mathrm{i}}_{3}{\mathrm{O}}_{12}$ (BNdT)] system exhibited the most remarkable ferroelectric properties. The $c$-axis oriented BNdT capacitor was characterized by a switchable remanent polarization $2{P}_{r}$ of over $100\text{ }\ensuremath{\mu}\mathrm{C}/{\mathrm{c}\mathrm{m}}^{2}$ and imprinting and fatigue-free behavior. The active Ti site responsible for the giant ${P}_{s}$ was identified with the help of Rietveld analysis, x-ray absorption near-edge structure study, and ab initio quantum computations.

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