Local and Global Ordering in Barium Zirconate, a Model Potential Study
Typ
Examensarbete för masterexamen
Master Thesis
Master Thesis
Program
Applied physics (MPAPP), MSc
Publicerad
2014
Författare
Fransson, Erik
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Barium zirconate (BaZrO3) is a promising candidate as proton conducting electrolyte to be used in fuel cells. Despite extensive investigations the basic structure of BaZrO3 as a function of temperature is not fully understood. It is related to possible instabilities in the cubic system that may show up in the local and/or global ordering of the material as a function of temperature. In this study three different types of simple models for barium zirconate are created, one giving rise to an ordinary cubic structure, one giving rise to distortion and one intermediate on the limit between the two others. All three models are based on a pair potential taking three types of interaction into account, Pauli repulsion, van der Waals interaction and Coulomb interaction. Static and dynamic properties obtained from computer simulations of the three models are presented to illustrate the different behaviours. The stability of the models are investigated by calculating phonon spectra. Molecular dynamics are used to study the time evolution of the system. The oxygen atoms for the model giving rise to distortion are found to move a lot more compared to the stable model, this is explained by the degenerated groundstate for the distorted structure. The obtained radial distribution function indicates that the distortions are not found for temperatures above 300 K, meaning that a phase transition happens. Furthermore for large systems the formation of clusters of different distortions are observed. Using these types of simple models created one could in an easy way compare experimental results with computer simulations to get a better understanding of instabilities in perovskites in general and barium zirconate in particular.
Beskrivning
Ämne/nyckelord
Den kondenserade materiens fysik , Materialvetenskap , Condensed Matter Physics , Materials Science