# Synthesis and characterisation of chemically modified schafarzikite and pyrochlore minerals

Whitaker, Mariana J. (2013). Synthesis and characterisation of chemically modified schafarzikite and pyrochlore minerals. University of Birmingham. Ph.D.

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## Abstract

Schafarzikite, FeSb$$_2$$O$$_4$$, is a tetragonal mineral (space group P4$$_2$$/mbc) belonging to a family of compounds with the general formula MX$$_2$$O$$_4$$. Schafarzikite has successfully been synthesised and chemically modified in various different ways. Lead has been substituted onto the pyramidal X sites to form compounds of formulation FeSb$$_{2-x}$$Pb$$_x$$O$$_4$$ (x = 0.2-0.75), excess oxygen ions have been incorporated into the structure to form FeSb$$_{2-x}$$Pb$$_x$$O$$_{4+y}$$ and compounds with mixed octahedral M ions, Fe$$_{1-x}$$Mg$$_x$$Sb$$_2$$O$$_4$$, have been prepared. The modifications give rise to changes in the magnetic ordering and magnetic structures and the conductivity of FeSb$$_{2-x}$$Pb$$_x$$O$$_4$$ is increased with respect to that of schafarzikite.

Pyrochlores (space group Fd-3m) have the general formula A$$_2$$B$$_2$$O$$_7$$. The structures of Bi$$_{2-x}$$Fe$$_x$$(FeSb)O$$_7$$ (x = 0.1, 0.2, 0.3) and Nd$$_{1.8}$$Fe$$_{0.2}$$(FeSb)O$$_7$$ have been studied and found to undergo static displacive disorder in the A$$_2$$O’ chains. Pyrochlore materials are magnetically frustrated and the samples Bi$$_{2-x}$$Fex(FeSb)O$$_7$$ (x = 0.1, 0.2, 0.3) display spin-glass behaviour. The magnetic properties of RE$$_2$$CrSbO$$_7$$ pyrochlores have also been investigated because, despite the inherent magnetic frustration in the pyrochlore structure, Ho$$_2$$CrSbO$$_7$$ is known to order magnetically at 10 K. Neutron diffraction showed that the Ho$$^{3+}$$ moments form an ordered spin-ice arrangement while the Cr$$^{3+}$$ moments order ferromagnetically.

Type of Work: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
Supervisor(s):
Supervisor(s)EmailORCID
Greaves Professor, ColinUNSPECIFIEDUNSPECIFIED
Licence:
College/Faculty: Colleges (2008 onwards) > College of Engineering & Physical Sciences
School or Department: School of Chemistry
Funders: Engineering and Physical Sciences Research Council
Subjects: Q Science > QD Chemistry
URI: http://etheses.bham.ac.uk/id/eprint/3944

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