Reversible Chemical Switching of a Ferroelectric Film

According to recent experiments and predictions, the orientation of the polarization at the surface of a ferroelectric material can affect its surface chemistry. Here we demonstrate the converse effect: the chemical environment can control the polarization orientation in a ferroelectric film. In situ synchrotron x-ray scattering measurements show that high or low oxygen partial pressure induces outward or inward polarization, respectively, in an ultrathin ${\mathrm{PbTiO}}_3$ film. Ab initio calculations provide insight into surface structure changes observed during chemical switching.

Figure 1

Hysteresis in $L$ scans through the 304 Bragg peak of a 10 nm ${\mathrm{PbTiO}}_3$ film at 644 K, at various oxygen partial pressures $p{\mathrm{O}}_2$. Plots (a) and (b) are for $p{\mathrm{O}}_2$ decreasing from a high value and increasing from a low value, respectively. Redder hues indicate higher intensity (log scale). Plots (c) and (d) show peak position and intensity; closed and open symbols are for decreasing and increasing $p{\mathrm{O}}_2$, respectively. To fully switch the sample at low $p{\mathrm{O}}_2$ (not shown), oxygen flow was set to zero, resulting in $p{\mathrm{O}}_2<{10}^{-7}\mathrm{mbar}$.

Figure 2

Analysis of scattering data for a 10 nm ${\mathrm{PbTiO}}_3$ film, showing ferroelectric response to ambient oxygen concentration. Closed and open symbols are for decreasing and increasing $p{\mathrm{O}}_2$, respectively. (a) ${\mathrm{PbTiO}}_3$ $c$ lattice parameter for three temperatures. Note that for 950 K, response to $p{\mathrm{O}}_2$ is minimal because $T$ is greater than $T_C$. Dashed lines are the zero-polarization values of $c$ for each $T$. (b),(c) Results of a structural model fit to $L$ scans for the 644 and 737 K data, deducing the fraction of positively polarized domains and the net polarization.