Controlling the Stiffness of a Material at the Nanoscale

Giant elastic tunability—the Young’s modulus changes reversibly over 30% under applied electric fields—was discovered in BiFeO₃ epitaxial thin films through an atomic force microscopy study utilizing band-excitation piezroresponse spectroscopy. These findings may lead to the development of high-performance tunable microwave filter devices based on BiFeO₃ as well as helping to further identify and/or design functional materials for these applications.

Ferroelectric materials possess electrically tunable elastic and dielectric susceptibilities due to the coupling between intrinsic phase transition lattice instabilities (so-called soft modes) and external fields. Here, the phase transition of BiFeO₃, induced by a biased tip in highly confined volumes (~10³ nm³), shows typical acoustic soft-mode behavior, and the local elasticity is quantitatively analyzed along with other complementary information channels including piezoresponse and acoustic loss. Further spatially-resolved measurements show the influence of heterogeneous domain structures on the phase transition kinetics. These observations, in conjunction with the phase-field modeling within the Landau-Ginzburg theoretical framework, provide a comprehensive understanding of the nanoscale polarization rotation and switching dynamics of BiFeO₃ and its link with the macroscopic functionalities. The methodology formulated in this work can be applied to many other ferroelectric materials, and may also provide clues for a wider spectrum of condensed matter systems where the phase transitions can be examined via local elasticity.

Q. Li, Y. Cao, P. Yu, R. K. Vasudevan, N. Laanait, A. Tselev, F. Xue, L.-Q. Chen, P. Maksymovych, S. V. Kalinin,  and N. Balke, “Giant Elastic Tunability in Strained BiFeO₃ Near an Electrically Induced Phase Transition,” Nature Commun. 6, 8985 (2015).  DOI: 10.1038/ncomms9985

For more information, please contact Nina Balke Wisinger, balken@ornl.gov