Researchers from Cornell University, Pennsylvania State University, and the University of California, Berkeley, have made a significant discovery in the field of materials science that could have implications for the energy industry. The team, led by Kaveh Ahadi and Venkatraman Gopalan, has demonstrated that KTaO3, a cubic perovskite in its bulk form, can be transformed into a highly tunable ferroelectric material when subjected to epitaxial strain.
Epitaxial strain is a process where a thin film of one material is grown on a substrate of another material, causing the film to adopt the lattice structure of the substrate. In this case, the researchers grew KTaO3 films on SrTiO3 substrates, which imposed an in-plane strain of -2.1% on the KTaO3. This strain transformed the cubic structure of KTaO3 into a tetragonal polar phase, with a transition temperature of 475 K. The researchers found that the Curie temperature and the spontaneous electric polarization of the KTaO3 could be systematically controlled by adjusting the epitaxial strain.
The researchers used scanning transmission electron microscopy to observe the cooperative polar displacements of the potassium columns with respect to the neighboring tantalum columns at room temperature. They also used optical second-harmonic generation to confirm the emergence of a global polar ground state, described by a tetragonal polar point group (4mm). Finally, they observed a ferroelectric hysteresis response using metal-insulator-metal capacitor test structures, demonstrating a robust intrinsic ferroelectric state in the epitaxially strained KTaO3 thin films.
The practical applications of this research for the energy industry are significant. Ferroelectric materials have a spontaneous electric polarization that can be reversed by an external electric field. This property makes them useful in a variety of applications, including capacitors, memory devices, and sensors. The ability to tune the ferroelectric properties of KTaO3 by adjusting the epitaxial strain could lead to the development of new and improved devices for the energy industry.
The research was published in the journal Nature Communications.
This article is based on research available at arXiv.