Frontiers of Materials Award Symposium: Intermetallic Alloys at the Edge of Complexity: Structural and Kinetic Aspects: Session II
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Phase Transformations Committee, TMS: Solidification Committee
Program Organizers: Ashwin Shahani, University Of Michigan
Thursday 8:30 AM
March 23, 2023
Room: 28C
Location: SDCC
Session Chair: Ashwin Shahani, University Of Michigan
8:30 AM Invited
In-Situ Growth of PtSn4, a Complex Layered Intermetallic: Lin Zhou1; Feng Zhang2; Jiaqi Yu1; Xiaotian Fang3; Wenyu Huang1; Matthew Kramer1; 1Ames National Laboratory; Iowa State University; 2Ames National Laboratory; 3Iowa State University
Complex layered intermetallic compounds are prone to defects and disorder that can dramatically affect their electronic properties. By encapsulating nano-particles of the Pt-Sn in silica, we could follow the nucleation and growth of the compound over multiple heating and cooling cycles to understand how processing can affect quality of crystal formation. The TEM images taken during cooling the liquid through the peritectic revealed the gradual formation of the 3D ordered PtSn4 phase from a 1D quasi-order to a 3D quasi-order structure over about 60°C. Density-functional theory (DFT) and a deep-learning neural-network (NN) potential calculations provided reliable structure and energetics for crystal phases and create training data for NN and embedded atom method (EAM) potentials. The NN and EAM potentials, in turn, expand the time and length scales of DFT, which were necessary to interpret experiments and help establish an adaptive control loop to improve quality of the crystal.
9:10 AM Invited
Direct Evaluation of Quasicrystal Bulk and Surface Energies in Density Functional Theory: Wenhao Sun1; 1University of Michigan
The discovery of quasicrystals forced solid-state chemists to revisit basic assumptions about crystallinity, bonding, and materials stability. A fundamental question emerged: Are quasicrystals thermodynamically stable? Or are quasicrystals metastable but nucleation-preferenced due to a low surface energy? Density functional theory is often used to evaluate thermodynamic stability, but quasicrystals are aperiodic and cannot be simulated using periodic boundary conditions. Here, we present a new technique to directly calculate the bulk and surface energies of quasicrystals in DFT. We compute the energies of quasicrystal nanoparticles with increasing sizes, and then fit the bulk and surface energies of the nanoparticles using a Gibbs-Thomson relationship. Using this technique, we evaluate the Tsai-type ScZn and YbCd icosehdral quasicrystals, whose structures have been resolved with atomistic resolution. From the bulk and surface energies, we construct size-dependent phase diagrams along with quasicrystal Wulff shapes, enabling us to establish the bulk and nanoscale (meta)stability of icosahedral quasicrystals.
9:50 AM Break
10:10 AM Invited
Complex Intermetallic Compounds: Original Surface Structures for Unusual Surface Properties: Emilie Gaudry1; 1Université de Lorraine
Complex intermetallic compounds (CIMCs) with bulk cage-like structures are a class of ordered alloys made of highly symmetric polyhedra as building blocks. Representatives of this family includes quasicrystals and their approximants, as well as intermetallic clathrates and related compounds with large crystal cells. Their unique structures can lead to unusual surface properties – at least when compared to those of conventional alloys -- which make them attractive for a number of applications, like efficient coatings, templates for building new molecular nano-structures or as novel catalytic materials. The detailed knowledge of surface structures is a necessary step to understand and tune the surface structure-property relationships. In this talk I will show that Density Functional Theory calculations, possibly combined with experimental surface science techniques, can be used to determine the thermodynamic, atomic and electronic structures of the CIMC stable surfaces. I will discuss the influence of the intrinsic bulk properties of the compounds, on their surfaces structures and properties.