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Deptartment of Physics
Yves U. Idzerda is currently a Professor of Physics at Montana State University. His current research interest is in characterizing and controlling ultra-thin film interface properties using novel characterization techniques that are element resolved and have strong interfacial sensitivity. Previous to this, he was the head of the Artificially Structured Materials and Non-linear Physics Section of the Naval Research Laboratory, where he was a staff member since 1989. He received his Ph.D in physics in 1987 from the University of Maryland with Prof. Ellen Williams. Part of this current research includes studying the behavior of components of solid oxide fuel cell thin films and surfaces/interfaces using in-situ and ex-situ X-ray probes. This portion of his research is performed at the MSU X-ray Nanomaterials Characterization Facility located at beamline U4B of the National Synchrotron Light Source (NSLS) of Brookhaven National Laboratories, where he has been the Spokesperson for this effort since its beginning.
Research Summary: X-ray Characterization of Operational SOFC Materials
One of the goals of the HiTEC program is to determine the effects of interfacial strain from lattice mismatch at interfaces of technologically relevant SOFC materials. For this work, the interfacial stress is controlled by either depositing SOFC-related films (La0.5Sr0.5CoO3, or LSCO, and La2/3Ca1/3MnO3, or LCMO) grown by pulsed laser deposition (PLD) or metal-organic chemical vapor deposition (MoCVD) on appropriate substrates of known lattice mismatch or by capping thick SOFC-related structures with wedges of overlayers of known lattice mismatch. This latter method allows for the control of the total stress energy with wedge thickness. We have used element- and site-specific X-ray spectroscopy and X-ray scattering to study the electronic, chemical and structural properties of the as grown systems.
By using polarization-dependent X-ray absorption spectroscopy (XAS), we have examined the chemical state of different elements of SOFC-related materials at room temperature as a function of the stress within the films created by the substrate or overlayer lattice mismatch that the film is grown under. We have found that, as the stress is changed from compressive to tensile stress, the chemical state of the transition metal in the interfacial region changes dramatically, although the structure of the film remains essentially unchanged. The compositional gradient region represents a region where not only the transition metal ion valence is changing, but a region where the oxygen vacancy diffusion is far from optimum, and in some extreme cases where the transition metal valance becomes integer valued, the oxygen vacancy diffusion may become negligible.
Through this research, we have identified a novel mechanism that may be a serious bottleneck to SOFC performance, whereby the strain energy at an SOFC interface is accommodated and distributed over a larger volume (thickness) by modifying the chemical construction of the SOFC material to improve the lattice mismatch.
- A. Lussier, J. Dvorak, S. Stadler, J. Holroyd, M. Liberati, E. Arenholz, S. B. Ogale, T. Wu, T. Venkatesan, and Y. U. Idzerda, "Stress Relaxation of La1/2Sr1/2MnO3 and La2/3Ca1/3MnO3 at Solid Oxide Fuel Cell Interfaces", Thin Films (accepted) (2006).
- J. Dvorak, Y. U. Idzerda, D. A. Arena, Y. G. Zhao, S. B. Ogale, T. Wu, T. Venkatesan, R. Godfrey, and R. Ramesh, "Are Strain-Induced Effects Truly Strain Induced? A Comprehensive Study of Strained LCMO Thin Films", J. Appl. Phys. 97, 10C102 (2005).