Nanoscale Phase Transition in Free-Standing Dielectric Thin Foils

Iowa State University, Ames IA

Investigators

Abstract

Non-technical description: Capacitors are essential elements in electronics. A group of oxide materials responding to electric fields by changing their atomic packing arrangements can display excellent properties for capacitor applications. This project utilizes advanced electron microscopy techniques to reveal the underlying microstructural mechanisms responsible for the electrical responses of the oxides at the nanometer scale in real time. The impact of mechanical stresses to such responses are examined. A new imaging technique is developed and applied to contrast the material's original and changed atomic structures. The outcome of the work is expected to be helpful in designing new materials for efficient capacitors, which are urgently needed in renewable energy sources and electric cars. In this project, educational activities are included to integrate undergraduate students, especially those from underrepresented groups, into the research. In addition, the research team presents demonstrations on capacitors in smart phone chargers to high school students visiting Iowa State University for the annual Science Bowl regional competition. Technical description: Ultrahigh energy capacitors are possible with antiferroelectric materials as dielectric layers. It is believed that implementation of such antiferroelectric capacitors in the next generation power electronics could improve their structural stability and energy efficiency. The ultrahigh energy density in antiferroelectric capacitors is achieved through repeated antiferroelectric - ferroelectric phase transition, which has only been investigated through macroscopic characterization of polarizations and strains so far. This research effort aims to directly visualize the nucleation and growth evolution of the new phase during this critical phase transition at nanometer spatial resolution in free-standing thin foils of antiferroelectric oxides using a unique in situ transmission electron microscopy technique developed by the PI's group. The influences of crystallographic orientation and structural defects, such as dislocations and grain boundaries, on the nucleation process are examined. In addition, electron holography technique is applied to determine the polarization direction of the polar ferroelectric phase, and to compare it with the nonpolar antiferroelectric phase. Such fundamental understanding of the phase transition is of critical importance for the successful implementation of antiferroelectric capacitors in future power electronics.