Investigation of the ferroelectric domain dynamics and its effects on macroscopic behaviors using a synchrotron X-ray photon correlation spectroscopy

NON-TECHNICAL SUMMARY Ferroelectric (FE) materials show spontaneous polarization that can be switched by an electric field. These materials consist of domains, the regions where the polarization is oriented in the same directions. FE materials have been used in various electronic devices such as infrared sensors, actuators, and ultrasound transducers. While it is well recognized that the modification of the domain configurations can enhance the electromechanical and dielectric properties of the FE materials, there is a knowledge gap regarding what is the ideal domain size or domain wall density (i.e., boundary regions between adjacent domains) to optimize the macroscopic material properties. The proposed research aims to develop an in-situ characterization method based on the X-ray photon correlation spectroscopy (XPCS). XPCS can investigate the dynamics of the atomic structures of materials over a range of time from milliseconds to hundreds of seconds in the mesoscale length (1 to tens of micrometers). This range is a critical to explaining the effect of atomistic phenomena on the macroscopic behavior and not efficiently accessible by the current existing techniques, such as X-ray diffraction and piezoresponse force microscopy. The newly proposed method compares the shift of X-ray images under applied electric field. The degree of shift will be statistically analyzed to reveal the mechanisms for electromechanical response in the material, including through continuous domain deformation or discrete domain wall motion. The outcome of this research will be a proof-of-concept of the viability of the above approach for further investigations of the effects of domain wall density and domain size on the FE material properties. Additionally, this proposal includes educational plans aimed at promoting STEM careers among underrepresented minority (URM) groups. These plans involve K-12 outreach initiatives, integrating STEM curriculum for university students, and providing research mentorship to high school and college students from URM groups. TECHNICAL SUMMARY The proposed research aims to investigate the fundamental mechanisms behind the ferroelectric (FE) domain engineering through proof-of-concept research distinguishing X-ray scattering behaviors associated with the intrinsic (i.e., domain extension and dipole rotation) and extrinsic (i.e., discrete domain wall motion) contributions to the electromechanical (i.e., piezoelectric) response. The proposed approach by X-ray photon correlation spectroscopy (XPCS) provides a fundamentally new method to investigate the domain and domain wall effects in the mesoscopic (one to tens of microns) range, which is a critical length scale explaining the effect of atomistic phenomena on the macroscopic material behavior. For comparison, the existing techniques based on X-ray diffraction can estimate domain switching on a macroscopic scale, by using the relative intensity of the corresponding diffraction peak. Furthermore, the theoretical estimation is limited to the domain configuration that can be perfectly described by the diffraction peaks used in the calculation. Similarly, while piezoresponse force microscopy can visualize FE domain patterns, it is difficult to characterize the dynamic atomic structure changes at the mesoscale, due to the scanning speed limitations. In contrast, XPCS acquires the scattering signals in a frame to track the pattern shift in all locations over milliseconds to hundreds of seconds. This project will use Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals to test if the statistical distributions of the XPCS decorrelation functions can distinguish between the effects of intrinsic and extrinsic responses. The goal is to develop a 'two-field' XPCS method and a statistical analysis tool for assessing the contributions of intrinsic and extrinsic mechanisms to the piezoelectric and dielectric properties. This project also aims to educate the next generation of engineers and scientists through multidisciplinary research involving materials science, X-ray characterization, and data science. The research outcome will be also used to educate K-12, undergraduate, as well as graduate-level students from underrepresented minority groups through various initiatives, such as outreach activities and innovative curricular efforts. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.