| Summary: | A computer modelling approach to the study of four compounds of the potassium yttrium fluoride (KYF) family is presented. These materials have been investigated using the General Utility Lattice Program (GULP), with respect to intrinsic defects and rare earth doping at both bulk and surface sites, with a view to their application in optical devices. A K-F potential, supplementing existing potentiaIs, has been fitted to these materials to generate computer models for which structural parameters show good agreement with experimental values. Studies have shown that the four materials respond to intrinsic defects in a similar manner with comparisons revealing anion Frenkel defects as the most favourable. Rare earth doping at bulk sites revealed that isovalent doping at yttrium sites is preferential to doping at potassium sites for all materials. Solution energies indicate that doping at yttrium sites becomes more favourable for latter series dopant ions. Charge compensatory mechanisms are required when doping at the potassium site, which have been shown to influence the energetic favourability of the doping process. Similar trends for each mechanism employed to each material have been observed. Comparisons of unbound and bound defects, when doping at potassium sites, have provided evidence that the interaction of defects has an important role in reducing the energetic cost of complex doping processes. Surface morphology diagrams have been produced along with surface energies for pure and doped surfaces. Segregation energies indicate that latter series rare earth dopants prefer bulk positions while earlier series dopants are likely to occupy surface sites. Additional studies have been performed with respect to the potential for the use of KY3FlO and KYF4 as solid electrolytes which showed encouraging results. Conclusions have been drawn indicating that rare earth doped compounds of the KYF family show potential for use in optical applications.
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