ANUlogo Structure of Oxides



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Overview

Oxide materials are of great scientific and commercial interest. High temperature superconductors, magnetoresistive materials, piezoelectrics, ferroelectrics, multiferroic materials -- all are found amongst the oxides.

We use diffraction techniques to look at the crystal structure of oxide materials. These structures can then be related to properties (magnetic, dielectric, and so on). The aim is to find new useful materials.

Oxides can be obtained as single crystals, which allows diffuse scattering studies to be performed, in which we look at the short-range order in the materials. This is particularly relevant in substituted and mixed oxides (for example PZN, PbZn1/3Nb2/3O3) where the ions on the mixed site (Zn/Nb in this case) do not go in in an ordered way. Here is a presentation concerning diffuse scattering and PZN.

Research Projects

Ferrates: Having done some work on cobaltates, we are looking at the structures of ferrate oxides based on the perovskite structure. The generic formula is ABO3, where the A site contains a mixture of Ca, Sr or Ba with a lanthanide, the B site is occupied by Fe and we have the possibility of vacancies on the O sites. In truth, the unit cell will usually be much bigger than the basic perovskite cube, so there will be some number of such formula units. We are also exploring the multiferroic oxides like BiFeO3, YMnO3 and their many derivatives.

Project Details: Powder Pattern
This study makes use of laboratory and synchrotron X-ray powder diffraction, neutron powder diffraction, electron imaging and diffraction, dielectric constant measurement, magnetic property measurement and Mössbauer spectroscopy, the latter two in collaboration with the School of Physical, Environmental and Mathematical Sciences at the ADFA campus of the University of New South Wales. Other collaborators include the Bragg Institute at ANSTO and other sections of the ANU.

The figure to the right show a powder diffraction pattern for Ce0.10Sr0.90CoO2.80 measured at 25K using neutrons at ANSTO. It shows magnetic as well as structural Bragg peaks, and so we are able to work out the magnetic structure.

Related publications include:

J.M.Hudspeth, G.A.Stewart, A.J.Studer and D.J.Goossens, 'Crystal and Magnetic Structures in Perovskite-related La1-xCaxFeO3-δ (x=0.2, 0.33)', Journal of Physics and Chemistry of Solids, 72 (2011) 1543-1547. DOI: 10.1016/j.jpcs.2011.09.014

Michael James, Liliana Morales, Kia Wallwork, Maxim Avdeev, Ray Withers and Darren Goossens, 'Structure and magnetism in rare-earth strontium-doped cobaltates', Physica B 385-386 (2006) 199-201.

M.James, K.S.Wallwork, R.L.Withers, D.J.Goossens, K.F.Wilson, J.Horvat, X.L.Wang and M.Collela, 'Structure and Magnetism in the Oxygen-Deficient Perovskites Ce1-xSrxCoO3-δ (x ≥ 0.90)', Mat. Res. Bull. 40(8) (2005) 1415-1431.

D.J.Goossens, K.F.Wilson, M.James, A.J.Studer and X.L.Wang, 'Structural and Magnetic Properties of Y0.33Sr0.67CoO2.79', Phys. Rev. B 69 (2004) 134411.

Unit Cell This figure shows the unit cell for the cobaltate Ho0.2Sr0.8CoO2.75. It is much larger than the basic perovskite cube, and some of the oxygen sites have vacancies on them. We have also explored its magnetic behaviour:

D.J.Goossens, K.F.Wilson and M.James, 'Structure and Magnetism in Ho1-xSrxCoO3-δ', Journal of Physics and Chemistry of Solids 66 (2005) 169-175).

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