Domain fluctuations in a ferroelectric low-strain BaTiO3 thin film

A ferroelectric ${\mathrm{BaTiO}}₃$ thin film grown on a ${\mathrm{NdScO}}₃$ substrate was studied using x-ray photon correlation spectroscopy (XPCS) to characterize thermal fluctuations near the $a/b$ to $a/c$ domain structure transformation present in this low-strain material, which is absent in the bulk. XPCS studies provide a direct comparison of the role of domain fluctuations in first- and second-order phase transformations. The $a/b$ to $a/c$ domain transformation is accompanied by a decrease in fluctuation timescales, and an increase in intensity and correlation length. Surprisingly, domain fluctuations are observed up to 25 \ifmmode^\circ\else\textdegree\fi{}C above the transformation, concomitant with the growth of $a/c$ domains and coexistence of both domain types. After a small window of stability, as the Curie temperature is approached, $a/c$ domain fluctuations are observed, albeit slower, potentially due to the structural transformation associated with the ferroelectric to paraelectric transformation. The observed time evolution and reconfiguration of domain patterns highlight the role played by phase coexistence and elastic boundary conditions in altering fluctuation timescales in ferroelectric thin films.