Center for Functional Nanomaterials Seminar

Transition-metal perovskites (ABO3) have generated interest in both research and industrial communities due to their physical properties. Structural distortion away from ideal cubic is one of the main factors that tailor the diverse physical properties in such materials. (S)TEM is an ideal tool for this type of study due to its capacity for simultaneous imaging and chemical analysis. Perovskite vanadates (AVO3) are chosen as the subject of study because their physical properties can be tailored by varying the A-site cations. Determination of the oxidation state of vanadium in complex oxides have been carried out by electron energy loss spectroscopy. SrVO3/LaAlO3 is then studied both experimentally and theoretically as a prototype system. Extra electrons have been detected on the interface layer, and further proven to originate mainly from a change in the local bonding configuration of V at the La-O terminated substrate surface. This result provides an important insight for predictive material design of novel functional interfaces.
The application of the (S)TEM techniques used for studying the perovskite vanadate systems are further extended to other compounds containing transition metal elements. The refractory minerals from Comet 81P/Wild-2 are investigated to study the formation of the early solar system. The relatively high Ti3+/Ti4+ ratio in fassaite and the presence of osbornite indicates that the refractory minerals formed in the inner solar nebula and were later transported to the outer solar system where the comet formed. This implies a much more dynamic and perhaps more violent solar nebula than was previously suspected.