The synthesis and characterisation of pyrochlore frameworks

Abstract

Structural studies have been undertaken on a wide range of pyrochlore phases, with a
focus on garnering a better understanding of the factors determining the formation and
behavior of these materials. Extensive structural characterisation has been undertaken
primarily using powder X-ray and powder neutron diffraction techniques to explore the
subtle structural changes that occur as a result of changes in composition on the two
interlocking networks that make up the pyrochlore structure.

Particular attention has been paid to hydrated beta-pyrochlore materials, using high
resolution TOF and constant wavelength PND to accurately determine the location and
orientation of the water molecules within the structure. The location of these molecules
has been shown to be directly correlated to the overall lattice dimensions of the
pyrochlore framework, with the subsequent molecular orientation and internal bond
angles changing to provide an optimum stabilization effect on the A-site cation.
Investigation into the effects of hydration upon the superconducting beta-pyrochlore
series AOs2O6.nH2O (where A = K, Rb and Cs) has also been investigated; with a
correlation between the structural changes, the degree of hydration and the onset of the
superconducting state being discussed.

Also presented is work seeking to determine the scope and effects of ion-exchange on
the A2O’ network of the pyrochlore framework, with several new phases synthesised and
other known phases extensively characterized along with a discussion regarding the
limits of what may be included in the pyrochlore framework.

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