Effect of correlated oxide electrodes on disorder pinning and thermal roughening of ferroelectric domain walls in epitaxial $\mathrm{Pb}{\mathrm{Zr}}_{0.2}{\mathrm{Ti}}_{0.8}{\mathrm{O}}_3$ thin films

We report the competing effects of disorder pinning and thermal roughening on ferroelectric domain walls as a function of temperature in epitaxial $\mathrm{Pb}{\mathrm{Zr}}_{0.2}{\mathrm{Ti}}_{0.8}{\mathrm{O}}_3$ thin films deposited on (001) $\mathrm{SrTi}{\mathrm{O}}_3$ substrates buffered by three types of correlated oxide electrodes, ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}\mathrm{Mn}{\mathrm{O}}_3$, $\mathrm{LaNi}{\mathrm{O}}_3$, and $\mathrm{SrIr}{\mathrm{O}}_3$. Piezoresponse force microscopy studies show that the 50-nm $\mathrm{Pb}{\mathrm{Zr}}_{0.2}{\mathrm{Ti}}_{0.8}{\mathrm{O}}_3$ films are uniformly polarized in the as-grown states, with the patterned domain structures persisting above 700 °C. For all three types of films, the domain wall roughness is dominated by two-dimensional (2D) random bond disorder at room temperature, and transitions to 1D thermal roughening upon heating. The roughness exponent $\zeta$ increases progressively from 0.3 to 0.5 within a temperature window that depends on the bottom conducting oxide type, from which we extracted the distribution of disorder pinning energy. We discuss the possible origins of the disorder pinning and the effect of the correlated oxide electrodes on the energy landscape of DW motion.

Figure 1

(a) Schematic experimental setup. CO: correlated oxide. (b)–(e) PFM characterizations of PZT/LSMO S1. (b) PFM amplitude and (c) phase switching hystereses. (d) PFM phase and (e) amplitude images of a domain structure written with $V_{\mathrm{bias}}=\pm 6$ V. The lower panels show the signal profiles along the dashed lines. (f) $B$($L$) at RT for three PZT samples. The dashed lines correspond to fits $\propto L^{2\zeta }$ with $\zeta =0.31$. Inset: Schematic of a rough DW.

Figure 2

PFM phase images of the same stripe domains at selected TQ temperatures. (a) PZT/LSMO S2. (b) PZT/LNO. (c) PZT/SIO S1. The RT images were taken after 24 h of initial writing. All images are shown at the same scale. The light (dark) color corresponds to the $P_{\mathrm{up}}\left(P_{\mathrm{down}}\right)$ domains.

Figure 3

(a) and (b) $\zeta$ vs $T$ obtained via in situ PFM imaging and the TQ method for (a) PZT/LSMO and (b) PZT/SIO. (c) $\zeta$ vs $T$ obtained via the TQ method for three types of PZT samples.

Figure 4

Schematic of DW motion in a disordered energy landscape (a) without and (b) with an external field. The particle represents the pinned DW, which can hop to a new position via thermal activation. (c) Schematic $\zeta -T$ diagram. (d)–(f) $\zeta$ vs $T$ in log-log scale for (d) PZT/LSMO, (e) PZT/LNO, and (f) PZT/SIO.