Understanding the Structure of Ferroelectric Nanocrystals

1. Understanding the Structure of Ferroelectric Nanocrystals Irving P. Herman, Columbia University, DMR 0213574 At low temperatures, materials like barium titanate undergo a transition to a state in which the charges of atomic ions do not balance each other. In this ordered ferroelectric state, this imbalance is called a permanent electric dipole moment. In barium titanate, this occurs in the bulk and in nanocrystals due to the displacement of titanium atoms from symmetric positions. Drs. Brus and Steigerwald of the Columbia MRSEC have learned that this displacement of titanium atoms is even larger in smaller nanocrystals than in larger nanocrystals, which is unexpected. This could impact forming electronic devices composed of very small amounts of ferroelectric materials. Schematic of how the atoms in barium titanate distort, with the displacement of the titanium atom, in the transition from the paraelectric (left) to ferroelectric (right) state Columbia University MRSEC 2007 Highlight (DMR 0213574)