INVESTIGATIONS OF TRANSPORT AND STRUCTURAL PROPERTIES OF CONDENSED PHASE SYSTEMS BY THE METHOD OF MOLECULAR DYNAMICS

PHILLIP ALLEN CHEESEMAN, Purdue University

Abstract

This thesis consists of a brief description of the Molecular Dynamics simulation method (MD), a review of MD studies, of systems having MX(,2) and MX(,4) stoichoimetries, with which the author was associated, and finally a report of results obtained from simulation studies of modeled NaMgF(,3) and MgSiO(,3) cubic perovskite structures. Information related to program usage has been included as an appendix. The studies of the ABX(,3) fluoride and silicate, undertaken to assess the possibility of superionic conductivity in the silicate, have been judged to indicate that the perfect cubic perovskite structure cannot be retained by the fluoride in the superionic conducting phase since the MD studies indicate no ion transport to occur in the perfect structure near the material's melting point. Two types of trial defects installed in both simulated compounds, however, appear to give rise to anionic diffusion corresponding to a superionic conductor. These are interchange of approximately 20% of the structure's cations within their unit cells and production of (TURN)11% AX vacancy pairs. The latter type of defect appears to be more strongly affected by the geometry of defective unit cells. A further conclusion is drawn that NaMgF(,3) and MgSiO(,3) may only be analogous w.r.t. anion transport in qualitative terms since the relative anion diffusivities between defect types were seen to behave differently for the fluoride and silicate.

Degree

Ph.D.

Subject Area

Chemistry

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