Mesoscale Phenomena in Functional Polycrystals and Their Nanostructures: Electronic, Thermal and Optical Phenomena
Sponsored by: ACerS Electronics Division
Program Organizers: Serge Nakhmanson, University of Connecticut; Edward Gorzkowski, Naval Research Laboratory; James Wollmershauser, U.S. Naval Research Laboratory; Seungbum Hong, KAIST; Javier Garay, University of California, San Diego; Pierre-Eymeric Janolin, CentraleSupélec
Wednesday 8:00 AM
October 12, 2022
Room: 412
Location: David L. Lawrence Convention Center
Session Chair: Serge Nakhmanson, University of Connecticut; Edward Gorzkowski, NRL; Javier Garay, UCSD
8:00 AM Keynote
A New Carbon Solid: Layered Amorphous Graphene — Its Structure, Cohesion and Space-projected Conductivity: Rajendra Thapa1; Chinonso Ugwumadu1; Kishor Nepal1; Jason Trembly1; David Drabold1; 1Ohio University
Using first principles molecular dynamics, we have shown that carbon with densities in a window around 2.4 gm/cc undergoes a disorder-order transition when annealed near 3000K. The network self-organizes and forms planes after 10-20 ps — planes of amorphous graphene, separated by approximately the experimental inter-plane distance of .33 nm in graphite. The amorphous graphene planes are sp2, but with ring disorder (pentagons, hexagons, heptagons etc.). The galleries are filled with a fairly homogeneous electron gas arising from the pi orbitals. The cohesion is not due to van der Waals (fluctuating dipole) interactions as sometimes asserted for graphite (since these effects are not included in our Hamiltonian). We observed graphitization even for a random initial configuration, leading to more defects than for an amorphous carbon initial state. For all the models, we discuss the electronic properties and the space-projected electronic conductivity, which provides real-space information about conduction pathways in materials.
8:40 AM
Conduction in Aluminum with Graphite and Graphene Additives: Kishor Nepal1; Chinonso Ugwumadu1; Rajendra Thapa1; Kashi Subedi1; David Drabold1; Keerti Kappagantula2; 1Ohio University; 2Pacific NorthWest National Labarotory
We briefly describe the role of defects (vacancies and a grain boundary) on electron transport in FCC Aluminum. Next, we study the structural, electronic, thermal and transport characteristics of Aluminum with graphene and graphite additives. We use the Kubo-Greenwood formula (KGF) and plane wave DFT to compute the DC conductivity as a function of temperature by performing a thermal average of the KGF over a classical trajectory. The Space-Projected Conductivity is used to visualize and quantify the effects of the impurities on transport.
9:00 AM
Structure, Charge Distribution and Electronic Transport Mechanism in Layered Amorphous Graphene: Rajendra Thapa1; Chinonso Ugwumadu1; Kishor Nepal1; David Drabold1; 1Ohio University
Layered amorphous graphene (LAG) was created using first principles molecular dynamics simulation involving annealing at 3000K starting with a model of amorphous carbon with density around 2.4 gm/cc. The process of LAG formation involves first a conversion of non-sp2 carbon atoms into sp2 forms, followed by a transition to a fully layered structure, which we report in atomistic detail. Each layer has all threefold atoms, but with pentagons and heptagons in addition to hexagons. Space-projected-conductivity (SPC) calculations show that the conduction active part of the network within a LAG layer involves atoms part of hexagonal rings. We studied the density dependence of LAG formation by carrying out the simulation over a wide range of densities from 1.0 g/cc to 3.5g/cc. Lattice dynamics of the system will be studied using both density functional theory and machine learning potentials to compare/contrast the findings.
9:20 AM
Micro/Nanostructure Effects on Thermal Conductivity and Optical Light Transmission—Designing High Performance Laser Ceramics: Javier Garay1; 1University of California, San Diego
Heat generation and thermally induced failure has been a major challenge for high-power applications in solid state lasers. Improvements in the solid-state laser ceramic fabrication process offer improved mechanical toughness and comparable thermal conductivity compared to single crystal counterparts. Equally enticing is the possibility of using materials with intrinsically superior thermal/mechanical properties that are not viable in the single crystal form. We will discuss the nano/microstructural effects on optical, thermal, and mechanical properties of polycrystalline ceramics, recent developments in a variety of commonly used crystalline laser materials, and potential future directions for more robust laser gain materials for high-power applications. It is argued that the engineering microstructure with both optical and thermal performances in mind might offer breakthrough improvements in laser gain media.
9:40 AM Invited
Synthesis, Processing, and Properties of High Performance Lead Free Electro-optic Ceramics: Alexander Dupuy1; Yasuhiro Kodera2; Javier Garay2; 1University of California, Irvine; 2University of California, San Diego
Electro-optic (EO) materials allow for the precise control of light using electrical signals, which is crucial for a number of photonic technologies. Composition limitations in electro-optic single crystals make bulk polycrystalline ceramics attractive for exploring new electro-optic compositions. Here we explore the ferroelectric, optical, and EO properties of bulk polycrystalline lead-free (1-x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (referred to as BZT-BCT or BXT) ceramics. We demonstrate that powder synthesis and densification strategies can be modified to reduce optical scattering and significantly improve transparency, allowing for viable EO ceramics. These densified ceramics exhibit a unique electric field induced phase transformation, resulting in EO properties that are comparable or superior to modern state of the art EO materials. Finally, we establish how processing and grain size can be used to tailor the optical and EO properties, greatly expanding the engineering design flexibility of EO devices.
10:10 AM Break
10:30 AM Invited
Fabrication and Properties of Multi-scale Architected Materials: Christopher Spadaccini1; 1Lawrence Livermore National Laboratory
This presentation will cover the latest work in advanced and custom additive manufacturing processes for the fabrication of multi-scale architected materials and functional devices. The concept of architected materials revolves around the notion that material properties are traditionally governed by the chemical composition and spatial arrangement of constituent elements at multiple length-scales. This usually limits material properties with respect to each other. For example, strength and density are inherently linked so that, in general, the more dense the material, the stronger it is in bulk form. We will review advanced additive micro- and nano-manufacturing techniques to create new material systems with previously unachievable property combinations. The performance of these multi-scale material constructs is fundamentally controlled by geometry at multiple length-scales, from the nano- to the macroscale, rather than chemical composition alone. These concepts can also be applied to functional materials such as those for supercapacitors, optical components, and fluidic systems.
10:50 AM Invited
Aerosol Deposition and Characterization of Complex Oxide Systems: Eric Patterson1; Sara Mills2; Heonjune Ryou1; James Wollmershauser1; Edward Gorzkowski1; 1U.S. Naval Research Laboratory; 2ASEE Post Doc
Aerosol deposition was used to produce thick-films with layer thicknesses between 10 to 50 microns. The bonding and densification of the film and film/substrate interface is facilitated by high pressure, impact and fracture of the particles, and some form of physical-chemical bonding. The films have microstructures characterized by XRD to have nano-grained crystallites and have been shown to have high residual stresses. This unique combination of crystallite size, stress and thick film results in unique properties compared to bulk ceramics of the same materials. Due to these high residual stresses, materials systems that exhibit either antiferroelectric properties in the bulk (such as NaNbO3) or stress-stabilized ferroelectric materials (such as HfO2), are natural alternatives to be studied via this technique. Deposition was performed onto metal substrates to facilitate the characterization of the electrical properties of the films; including permittivity as a function of temperature.
11:10 AM Invited
From Nanoparticles to Nanocrystalline Solids with New Functionalities:
Thermoelectrics as a Case Study: Boris Feygelson1; James Wollmershauser1; Kevin Anderson1; Benjamin Greenberg1; Alan Jacobs1; 1US Naval Research Laboratory
Scaling grains down to nanometer size enhances many properties of polycrystalline solids due to an increase of the grain boundary interfacial volume fraction. Sintering of nanoparticles is the most versatile way to produce nanocrystalline solids of various materials. It is well established that the main prerequisite for obtaining such size dependent properties in these materials is removing porosity while preserving nanoscale morphology and grain size. Furthermore, these nanoparticle building blocks can be engineered by designing and synthesizing core/shell structures. By sintering core/shell nanoparticles to a fully dense solid while preserving their initial design, novel bulk materials can be fabricated with properties controlled by rationally designed core/shell geometries and properties, and the resultant vast network of interfaces.We exploit this possibility in order to improve thermoelectric material performance by engineering the properties of nanoparticle cores, shells, and interfaces and spatially decoupling interdependent thermal and electronic transport properties at the nanoscale.
11:40 AM
Modeling Thermoelectric Properties of Polycrystalline Materials at Mesoscale: Dharma Raj Basaula1; Mohamad Daeipour1; Lukasz Kuna2; John Mangeri3; Boris Feygelson2; Serge Nakhmanson1; 1University of Connecticut; 2U.S. Naval Research Laboratory; 3Luxembourg Institute of Science and Technology
A finite element method-based approach has been developed for evaluating the thermoelectric properties of polycrystalline materials at the mesoscale. This approach was first validated for isotropic systems by simulating effective Seebeck effect in a thermocouple and Peltier cooling at an interface between two dissimilar materials, obtaining good agreement with prior experimental or computational results. The developed approach was then used to model coupled heat and electrical current flow through an anisotropic polycrystalline material, providing local temperature and electric potential distributions under different applied conditions. This computational framework establishes the foundation necessary to elucidate the intricacies of coupled thermal and electric conduction through geometrically complex materials, including polycrystals, nanostructures and nanocomposites, and could provide new insights for improvement of their operational efficiency.
12:00 PM
Polycrystal-inspired Stochastic Mechanical Modeling of Complex, Heterogeneous Porous Microstructures: Mujan Seif1; Matthew Beck1; 1University of Kentucky
The inherent complex, disordered, and porous microstructure of Duocel aluminum foam makes predictive modeling of its mechanical properties difficult. Its randomly oriented constituent ligament structure also creates significant variability in properties at different length scales. An understanding of the transition from micro- (local) to macro- (bulk) length scales is critical to quantifying the effects of various inhomogeneities like inclusions, cracks, etc. To this end, we utilize a homogenizing approach inspired by those applied to polycrystals. Rather than simplifying the material such that its unique characteristic structural features are neglected, we present a stochastic modeling approach that integrates complex structure and predicts elastic mechanical behavior in the form of statistical distributions—as opposed to arithmetic means—of properties. Here, we compute these distributions as a function of cavity orientation and volume, as well as overall length scale.