Title:	Electronic-Structure and Atomic-Scale Computations for the Physics of Materials and Interfaces
DNr:	SNIC 2013/1-208
Project Type:	SNIC Medium Compute
Principal Investigator:	Göran Wahnström <goran.wahnstrom@chalmers.se>
Affiliation:	Chalmers tekniska högskola
Duration:	2014-01-01 – 2015-01-01
Classification:	10304
Homepage:	http://fy.chalmers.se/~tfsgw
Keywords:

Abstract

In this project we will focus on oxide materials and hard metals. For the oxide materials our primary interest is on ionic and electronic transport properties. In the case of hard metals we focus on interface related properties as mechanical strength and the sintering mechanism. We emphasis the atomic-scale approach and electronic-structure calculations are a key component. The project is divided into three subprojects. 1. Grain boundary barriers in solid state proton conductors While the benefits of ceramic materials make solid oxide proton conductors desirable for use as electrolyte materials in electrochemical devices such as hydrogen fuel cells, limitations in proton conductivity have thus far prevented successful implementation. It has become clear that in one of the more important candidate materials the perovskite oxide barium zirconate (BZO), the boundaries between grains in the material are the prime source of inhibited proton conductivity. Based on our previous findings we now would like to achieve a more complete understanding of how point defects interact with each other in the grain boundary and how this may affect the conductivity. DFT will be used for detailed energetic calculations and evaluation of electronic properties, while computationally less demanding model potential calculations allow us to study larger systems. 2. Hydration and oxidation of solid state proton conductors The aim with this subproject is to characterize different mechanisms that affect the proton uptake and the overall conductivity, ionic and electronic. We will do this by using DFT to study the energetics of point defect and defect complexes. In order for this to be done properly it is important to have an accurately described band gap, position of valence and conduction bands. We will derive that by using the more computationally demanding hybrid xc-functional and the GW method. For the elementary proton transfer process the computationally demanding RPA technique will be used. 3. Plastic deformation of cemented carbides Due to the success of various coatings in cemented carbides in recent decades, abrasive wear has become less of an issue, and instead, high temperature plastic deformation of the bulk material is often limiting tool life. There is evidence to support that grain boundary sliding occurs at these temperatures and that it is facilitated by binder phase grain boundary infiltration. In this project we will use both DFT based calculations and molecular dynamics using interatomic potentials. We will study the effects of temperature, deformation rate, and Co binder phase concentration in the boundary on sliding and decohesion. Stresses will be obtained as function of interface sliding and separation distance. We will investigate grain boundary sliding behavior of WC bicrystals and this will be used in collaboration with the Applied Mechanics group at Chalmers to calibrate cohesive zone laws for use in continuum models. These models will enable direct comparisons with experimental stress-strain curves.