Materials adopting the apatite structure are gaining an increasing importance as potential solid-oxide fuel cell electrolytes and for the chemical stabilisation of high level nuclear waste. The first part of this experiment is a structural investigation of the fuel cell electrolyte La10(GeO4)5(GeO5)O2 that has shown to exhibit a triclinic to hexagonal structural transition at high temperature (>600C) and which is accompanied by a change in conductive properties. This work will provide a greater understanding of this structural transition and help provide a better insight into the oxide ion conduction processes.The second part of this project is a crystallochemical study of a family of lanthanide silicates Ca2(RE)8(SiO4)6O2, RE = Pr, Nd, Tb, Ho and Yb that will be used to simulate waste compositions.