Antimony containing minerals as signposts to new functional materials

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• Prof. Colin Greaves, School of Chemistry, University of Birmingham
• Friday 04 May 2012, 14:00-15:00
• Physics East 217.

If you have a question about this talk, please contact Elizabeth Blackburn.

Antimony and bismuth both exist as M3+ and M5+ species, but whereas the two oxidation states have similar stability for bismuth, giving mixed oxidation states on the same site in superconducting (Ba,K)BiO3, antimony is significantly more stable as Sb5+. Nevertheless, in the lower Sb3+ state, mineral samples suggest an interesting chemistry because of low dimensional features that are linked to the inherent asymmetric coordination preferences for Sb3+, originating from its lone pair of electrons. Schafarzikite, FeSb2O4, has parallel chains of edge-linked FeO6 octahedra separated by empty channels (Fig.1). The rare minerals apuanite and versiliaite are structurally related to schafarzikite, but the channels are partially occupied by sulfide ions, which produce partial oxidation of the Fe2+ ions within the chains of octahedra. Fe2+  Fe3+ charge order within the chains depends on the sulfide content.

In this presentation we will describe:

• the magnetic structures and variation in ASb2O4, A = Mn – Ni;

• the first chemical control of the Fe oxidation state by cation substitution in FeSb2O4; • the first mixed cation phases with this structure;

• oxygen insertion into schafarzikite structures;

• the first synthesis of the minerals apuanite and versiliaite, and aspects of magnetic order;

• oxygen insertion within these structures.

The pyrochlores Ho2Ti2O7 and Dy2Ti2O7 are of current interest because of magnetic frustration resulting in magnetic spin-ice properties. Antimony in the higher Sb5+ oxidation state can substitute on the small (Ti) cation site in pyrochlore minerals, and we will consider some new magnetic and neutron diffraction data on spin-ice related pyrochlores, e.g. Ho2CrSbO7. In this particular material, the highly degenerate spin-ice ground state is replaced to give a ferromagnetic material below 13 K. The nature and origin of this change will be discussed.

This talk is part of the Condensed Matter Physics Seminars series.

This talk is included in these lists:

• Bham Talks
• Cond. Mat. seminar
• Condensed Matter Physics Seminars
• Physics East 217
• What's on in Physics?

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