1. D. A. Freedman, D. Roundy, and T. A. Arias, Phys. Rev. B 80, 064108 (2009).

1. For more details, visit the Cornell Center for Materials Research at www.ccmr.cornell.edu The Case of the Missing Oxygen AtomsTheory and experiment work together to improve high-performance electronic materials Advanced electronic materials known as perovskites have a wide range of impressive magnetic and electronic properties that could be useful in many high-tech applications; however, missing oxygen atoms have been a major problem in these materials. Even a single missing oxygen atom — or “oxygen vacancy” — can degrade the performance of nanoscale devices. To understand the puzzling shortage of oxygen atoms, researchers at Cornell made atomic-scale models of strontium titanate (SrTiO3) and calculated the effects of removing individual atoms. Surprisingly, the removal of a single oxygen atom had almost no effect on the crystal! Nearby atoms simply rearranged into a new configuration that caused no large-scale puckering or distortion. Armed with these calculations, the researchers used high-intensity x-ray beams to take pictures of the defective crystals and confirm theoretical predictions. Since all materials have defects on the atomic scale, understanding defects is crucial for the development of next-generation electronics. When an oxygen atom (blue) is removed from a SrTiO3 crystal, some atoms move towards the hole (red arrows), whereas others move away (green arrows). As a result, there is no net effect on the crystal. This theoretical prediction1 has been confirmed by x-ray scattering measurements.2 1. D. A. Freedman, D. Roundy, and T. A. Arias, Phys. Rev. B 80, 064108 (2009). 2. Y. Kim, T. Babakol, A. Disa, and J. D. Brock (submitted 2010) DMR 0520404