Effects of sublattice symmetry and frustration on ionic transport in garnet solid electrolytes

We use rigorous group-theoretic techniques and molecular dynamics to investigate the connection between structural symmetry and ionic conductivity in the garnet family of solid Li-ion electrolytes. We identify new ordered phases and order-disorder phase transitions that are relevant for conductivity optimization. Ionic transport in this materials family is controlled by the frustration of the Li sublattice caused by incommensurability with the host structure at non-integer Li concentrations, while ordered phases explain regions of sharply lower conductivity. Disorder is therefore predicted to be optimal for ionic transport in this and other conductor families with strong Li interaction.Comment: 6 pages, 4 figures, and supplementary informatio

Mechanical testing ontology for digital-twins: A roadmap based on EMMO

The enormous amount of materials data currently generated by high throughput experiments and computations poses a significant challenge in terms of data integration and sharing. A common ontology lays the foundation for solving this issue, enabling semantic interoperability of models, experiments, software and data which is vital for a more rational and efficient development of novel materials. This paper is based on the current efforts by the European Materials Modelling Council (EMMC) on establishing common standards for materials through the European Materials & Modelling Ontology (EMMO) and demonstrates the application of EMMO to the mechanical testing field. The focus of this paper is to outline the approach to develop EMMO compliant domain ontologies

An epitaxial model for heterogeneous nucleation on potent substrates

© The Minerals, Metals & Materials Society and ASM International 2012In this article, we present an epitaxial model for heterogeneous nucleation on potent substrates. It is proposed that heterogeneous nucleation of the solid phase (S) on a potent substrate (N) occurs by epitaxial growth of a pseudomorphic solid (PS) layer on the substrate surface under a critical undercooling (ΔT ). The PS layer with a coherent PS/N interface mimics the atomic arrangement of the substrate, giving rise to a linear increase of misfit strain energy with layer thickness. At a critical thickness (h ), elastic strain energy reaches a critical level, at which point, misfit dislocations are created to release the elastic strain energy in the PS layer. This converts the strained PS layer to a strainless solid (S), and changes the initial coherent PS/N interface into a semicoherent S/N interface. Beyond this critical thickness, further growth will be strainless, and solidification enters the growth stage. It is shown analytically that the lattice misfit (f) between the solid and the substrate has a strong influence on both h and ΔT ; h decreases; and ΔT increases with increasing lattice misfit. This epitaxial nucleation model will be used to explain qualitatively the generally accepted experimental findings on grain refinement in the literature and to analyze the general approaches to effective grain refinement.EPSRC Centre for Innovative Manufacturing in Liquid Metal Engineerin

First-principles density functional theory study of native point defects in Bi2Te3

We present a first-principles study of the native point defects in the thermoelectric material Bi2Te3. Calculated formation energies of defects and electronic densities of states were analyzed in detail. The most prominent native point defects considered are vacancies and antisite defects on the Bi, Te1, and Te2 sublattices of the Bi2Te3 structure. Vacancies on all three sublattices are found to have much higher formation energies than antisite defects. The most dominant antisite defects are found to be BiTe1 at Bi-rich conditions, and TeBi at Te-rich conditions. These lead to the formation of resonant defect states at the top of the valence band and bottom of the conduction band, respectively. Hence they are expected to impact charge and energy transport in a profound way. Furthermore antisite defect pairs tend to form at nearest-neighbor distances, and lead to substantial changes in the electronic structure and hence in the thermoelectric properties of Bi2Te3

Ab initio study of electronic densities of states at copper-alumina interfaces

The electronic structure of Cu(1 1 1)/alpha-Al2O3(0 0 0 1) interfaces with two experimentally observed orientation relationships were studied in terms of local site and angular-momentum-projected electronic densities of states. The electronic band structures were calculated using density functional theory in the local density approximation. The local densities of unoccupied states are compared with experimentally determined electron energy loss near-edge structures. A very good coincidence was found for the interfacial oxygen and aluminum atoms. Interpretation guidelines for the electron energy-loss near-edge structures (ELNES) are suggested for further experimental measurements. The local bonding across the interface is analyzed in terms of local densities of occupied states

A DEM contact model for history-dependent powder flows

Die filling is an important part of the powder handling process chain that greatly influences the characteristic structure and properties of the final part. Predictive modelling and simulation of the die-filling process can greatly contribute to the optimization of the part and the whole production procedure, e.g. by predicting the resulting powder compaction structure as a function of filling process parameters. The rheology of powders can be very difficult to model especially if heterogeneous agglomeration or time-dependent consolidation effects occur. We present a new discrete element contact force model that enables modelling complex powder flow characteristics including direct time-dependent consolidation effects and load history-dependent cohesion to describe the filling process of complex, difficult to handle powders. The model is demonstrated for simple flow and an industrial powder flow