Research

Owing to the variety of systems studied in the Grosvenor group and the large number of tools used to investigate them, a
variety of projects are available for graduate and undergraduate students to work on which can focus on synthesis, X-ray
spectroscopy, surface analysis or a combination of these.

The long-term goal of this research program is the investigation and development of ordered compounds containing small
elements that sequester uranium (U) in the structure. To this end, it is important to examine model compounds as host
materials in order to gain a clear understanding of the relationship between crystal structure, composition, bonding,
electronic structure, and surface reactivity to the sequestration of actinides such as U. The materials being studied by the
Grosvenor group have been chosen because their structure-types are common in nature and all contain sites large enough,
and with a high enough coordination number, to contain U. All materials being synthesized are studied by X-ray diffraction
(XRD), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS), utilizing synchrotron radiation.

Current research projects:
Electronic structure of group IV silicates: Natural zircons (ZrSiO4, Zr1-xHfxSiO4) are often found to be a source of
U and synthetic versions have been proposed in the past as candidate materials for radioactive waste immobilization [1-3].
The amorphous silicates, on the other hand, have received considerable attention from the semiconductor community
[4-10]. As semiconductor devices decrease in size, the tunnelling current that leaks through the SiO2 gate oxide layer
increases, affecting device reliability [11]. Because of this problem, alternatives for SiO2 based gate dielectric materials are
being sought with high k dielectrics like (HfO2)x(SiO2)1-x showing promise. XPS studies of these materials have shown
that the Hf 4f and Si 2p XPS binding energies (BE) shift depending on the value of x [6]. Variations in XPS BEs and XAS
absorption energies are generally related to interactions between the excited atom and its nearest neighbours. However,
the shifts observed in these transition-metal silicates arise because of a next-nearest neighbour (NNN) effect resulting
from the substitution of Si for Hf in the Si-O-Si bond [6]. NNN effects are a product of changes in the initial or final state
energies of the nuclear charge of the excited atom by atoms in the second coordination shell, and there is disagreement
regarding which one plays the major role.To study how these materials change with composition, heat treatment (e.g.,
thermal cycling), and production method, it is necessary to understand why binding and absorption energies shift.
Members of the Grosvenor group are studying these silicates, as well as other materials, to increase our understanding of
how XPS and XAS lineshapes and energies are influenced by substitution.

Oxidation behaviour of rare-earth filled and unfilled skutterudies (REM4Pn12, CoPn3): Transition-metal
(M) and rare-earth (RE) containing pnictides (REM4Pn12), having the skutterudite structure have been studied in the
past as potential thermoelectric materials which can be used for power generation and refrigeration applications [12,13].
The crystal structure consists of a network of corner-sharing metal-centred octahedra, which are tilted to form Pn4
squares creating large voids in the form of dodecahedral cages of Pn atoms [12,13]. Within these voids, RE atoms can be
present and actinide (U, Th)-containing analogues are known. It is because of these Pn cages that these materials may be
useful for waste sequestration. However, it is unknown how the RE, Pn, and M atoms will be effected when these materials
are exposed to reactive gases. In this investigation, students are studying the surface and bulk oxidation of RE containing
skutterudites, REM4Pn12 (RE = La, Ce, Eu, Gd; M=Fe, Ru, Os; Pn = P, As, Sb), by XPS and XAS after exposure to various
gases.

Electronic structure and Oxidation behaviour of Pyrochlores and Zirconolites: Of the systems being
examined for use in nuclear waste sequestration applications, the pyrochlore and zirconlolite phases have been studied the
most [14-16]. Materials adopting either the zirconlite (A2B2O7; A = Ca, V, Zr, Ti; B = Ti, Nb, Ta, Zr, Hf; X/X' = O, F, OH)
or pyrochlore (A2B2X6X'; A = Ca, Mn, Fe, rare-earths (RE), Gd; B = Ti, Nb, Ta, Zr, Hf; X/X' = O, F, OH) structure can
have a variety of chemical compositions [14,15]. Along with being able to incorporate actinides and being examined for
possible sequestration applications, these materials have also been studied for their catalytic and magnetic properties [14].
The focus of these studies is the investigation of Hf, Zr, and Ti containing systems by XAS and XPS owing to their
suitability for sequestration applications (e.g., Yb2Ti2-yFeyO7-x, RE2ZryTi2-yO7) [14,17]. As metals having vastly
different electronegativity values can be substituted into these compounds, it is expected that next-nearest neighbour
effects will shift the XPS binding energies, providing another opportunity to examine how and why this effect occurs.

Available 483.6 and 482.3 research projects:
One research projects will be offered during the 2010/2011 school year. This project has been designed for a student
registered in 483.6, however, it could be tailored to be suitable for a studen registered in 482.3. A brief description of the
the project offered can be found here.

Selected References:
1) Finch, R. J.; Hanchar, J. M. Rev. Mineral. Geochem. 2003, 53, 1-25.
2) Farges, F.; Calas, G. Am. Mineral. 1991, 76, 60-73.
3) Murakami, T.; Chakoumakos, B. C.; Ewing, R. C.; Lumpkin, G. R.; Weber, W. J. Am. Mineral. 1991, 76, 1510-1532.
4) Jin, H.; Oh, S. K.; Cho, Y. J.; Kang, H. J.; Tougaard, S. J. Appl. Phys. 2007, 102, 053709/1-6.
5) O'Connor, R.; Hughes, G.; Glans, P.-A.; Learmonth, T.; Smith, K. E. Appl. Surf. Sci. 2006, 253, 2770-2775.
6) Opila, R. L.; Wilk, G. D.; Alam, M. A.; van Dover, R. B.; Busch, B. W. Appl. Phys. Lett. 2002, 81, 1788-1790.
7) Lucovsky, G.; Rayner Jr., G. B; Kang, D.; Appel, G.; Johnson, R. S.; Zhang, Y.; Sayers, D. E.; Ade, H.; Whitten, J. L. Appl. Phys. Lett. 2001,
79, 1775-1777.
8) Mountjoy, G.; Anderson, R.; Newport, R. J.; Smith, M. E. J. Phys.: Condens. Matter 2000, 12, 3505-3519.
9) Abe, Y.; Miyata, N.; Ikenaga, E.; Suzuki, H.; Kitamura, K.; Igarashi, S.; Nohira, H. Jpn. J. Appl. Phys. 2009, 48, 041201.
10) Liu, J.; Wu, X.; Lennard, W. N.; Landheer, D. Phys. Rev. B 2009, 80, 041403.
11) O'Dell, L. A.; Gunawidjaja, P. N.; Holland, M. A.; Mountjoy, G.; Pickup, D. M.; Newport, R. J.; Smith, M. E. Solid State Nucl. Magn. Reson.
2008, 33, 16-24.
12) Nolas, G. S.; Morelli, D. T.; Tritt, T. M. Annu. Rev. Mater. Sci. 1999, 29, 89-116.
13) Sales, B. C. In Handbook on the phyiscs and Chemistry of Rare Earths; K. A. Gschneidner, J.-C. Bunzli and V. K. Pecharsky, Ed.; Elsevier,
Amsterdam, 2003; Vol. 33; pp 1-34.
14) Ewing, R. C.; Weber, W. J.; Lian, J. J. Appl. Phys. 2004, 95, 5949 - 5971.
15) Harvey, E. J.; Whittle, K. R.; Lumpkin, G. R.; Smith, R. I.; Redfern, S. A. T. J. Solid State Chem. 2005, 178, 800-810.
16) Perera, D. S.; Begg, B. C.; Vance, E. R.; Stewart, M. W. A. J. Mater. Online 2005, 1-7.
17) Horovistiz, A. L.; Fagg, D. P.; Abrantes, J. C. C.; Frade, J. R. J. Eur. Ceram. Soc. 2007, 27, 4283 - 4286.