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.

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