Teoretisk undersökning av bulkstrukturer av YSZ och en tvillinggräns av t-ZrO2 med DFT

Sammanfattning: The material yttria-reinforced zirconia (YSZ) is widely used in biomedical applications and is the latest material in dentistry for the production of dental implants such as crowns and bridges. The used concentrations of yttria in zirconia are usually between 3-8 mol% Y2O3 dissolved in the ZrO2 structure, which stabilizes ZrO2 in tetragonal structure at RT. The tetragonal structure is sufficiently hard without being too brittle and is therefore desirable in dental applications. Newer crowns use a combination of 3 and 5 YSZ in layers. The interface between these layers has not yet been investigated. We present here a DFT study on 3 and 5 YSZ. The density functional analysis (DFT) method is a common quantum mechanical method in materials science which, by calculating electron density, can calculate the total energy and hence conclusions can be drawn about the stability of the system. In previous studies, YSZ has been studied as bulk structure or as twin boundary in cubic structure. In this study, in addition to bulk structures, a twin boundary of t-ZrO2 is constructed. The approach was to initally construct bulk structures of 3 and 5 YSZ and analyze them using DFT in order to study the stability of the structures and compare to previous studies. Formation enthalpies were calculated for both systems and show that ¡result¿. Theoretical XRD spectra have been developed for the bulk structures. The results for the formation entalpy of the bulk structures indicate no stabilizing effect of the yttria doping suggesting some error in the proceedure, one theory being the choice of zirconium atoms that were selected to be substituted for yttrium atoms in the bulk structures. This needs to be investigated further. Moreover, the result from the XRD spectra confirmed that the introduction of Y2O3 into the ZrO2 structure led to perturbations in the crystallinity. A symmetrically coherent grain boundary at the 101 plane in t-ZrO2 was also created and its grain boundary energy was calculated to be 1.49 J/m2. The result suggests that the constructed grain boundary is a stable, coherent Σ3 boundary. The next step following up on this study would be to introduce 3 and 5 mol% Y2O3 to the Σ3 boundary.