Research Highlight

Controlling the Stiffness of a Material at the Nanoscale

Measured spectrograph (elastic stiffness/ piezoresponse versus tip bias) tracking local bias-induced rhombohedral to tetragonal phase transitions in BiFeO3 (BFO); the observed elastic softening phenomena are driven by the soft-mode phase transition dynamics. 

Giant elastic tunabilty—the Young’s modulus changes reversibly over 30% under applied electric fields—was discovered in BiFeO3 epitaxial thin films

Controlling the Stiffness of a Material at the Nanoscale Measured spectrograph (elastic stiffness/ piezoresponse versus tip bias) tracking local bias-induced rhombohedral to tetragonal phase transitions in BiFeO3 (BFO); the observed elastic softening phenomena are driven by the soft-mode phase transition dynamics.  (hi-res image)
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

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