4:00pm - 4:30pmInvited
Nano-Thermal Conduction in Layered Thermoelectric Oxides
1Osaka University, Japan; 2Japan Fine Ceramics Center, Japan
Demands for controlling heat in nanometer dimension is surging as devices and circuit are approaching atomic dimension these days. Yet, understanding of thermal conduction have been lagged behind electronic counterparts for many decades since emergence of semiconductors. Conventional theories for thermal conduction are constructed based on simple metals and semiconductors of relatively symmetric crystal structures and thus are not capable of predicting thermal conductivity of materials with low-symmetric crystal structures and of acquiring physical insights about mechanism behind the thermal conduction. As phonons are defined in reciprocal space, low-symmetric crystal structures result in multiple-folding of phonon dispersion curves in Brillouin zone, making it difficult to extract useful information even of stationary harmonic phonon states.
With an analogies to macroscopic brick layered model, modest thermal conduction for electronic conductors in layered thermoelectric oxides have been attributed to low thermal conductivity of nanometer-thick constituent layers that sandwich the primary layers for electronic conduction, even though assuming parallel circuit of heat conduction does not yield such a low thermal conductance as confirmed by experiments. We have done detailed analyses, using perturbed molecular dynamics we developed, of the atomistic mechanism of the nano-thermal conduction that is responsible for remarkable thermoelectric energy conversion efficiency, in order to find out the ways to further control the nano-thermal conduction.
It is found, against earlier speculations, that what suppress lattice thermal conduction without deteriorating electronic conduction in the layered thermoelectric oxides includes interlayer interaction, both static and dynamic, across interfaces included in those low-symmetry crystal structures. Each layer in an oxide plays different role, depending on oxides and on the combinations of layers. The procedure of the analysis and possible suggestion to further control thermal conduction based on the mechanisms revealed will be discussed in the presentation.
4:30pm - 5:00pmInvited
Computational Materials Design and Characterisation for Energy Harvesting and Energy Storage Materials
University of Oslo, Norway
High-throughput computational materials design is an emerging area of materials science and technology. By combining advanced computational methods with intelligent database construction, and exploiting the power of current supercomputer architectures one can generate, manage and analyse enormous data repositories for the discovery of novel materials for energy-related technologies. Although the demand for materials is endlessly growing, experimental discovery is bound by high costs and time-consuming procedures of synthesis. Computational materials science is an alternative burgeoning area for computational materials design. It is based on the bridge between computational quantum-mechanical, thermodynamic and spectroscopic approaches. In this presentation, we are going to present out recent activities on battery materials and light-absorbing materials for photovoltaic applications. Although a commercial success, lithium ion batteries are still the object of intense research mainly aimed to the characterization of improved electrode and electrolyte materials. We have modelled relative stability, electronic structure, thermodynamical, electrochemical and mechanical properties of several potential cathode and electrolyte materials for Li/Na ion batteries. This study presents a review of our recent progress dedicated to the electrode and electrolyte materials that have the potential to fulfil the crucial factors of cost, safety, lifetime, durability, power density, and energy density. Nanostructured inorganic compounds have been extensively investigated. Recently we have also examined over 15,000 inorganic materials using first-principles electronic structure calculations. Based on this approach, we propose computational materials design for high efficiency and low price solar cell materials based on non-silicon based compounds.
5:00pm - 5:15pmOral
Exploiting Polymer Topology for Surface Modification of Thermoplastics
1University of Kwazulu-Natal, South Africa; 2University of Akron, United States
Dynamical and structural properties of polymers in the melt state are strongly influenced by molecular architecture [1-4] and it is a subject of both industrial and fundamental interest. Blending polymers with different molecular topologies could be relevant to control interfacial segregation of the polymer film, and to achieve optimal mechanical properties of the plastic material [5,6]. However, a deep understanding of the role of chain architecture and molecular mass in determining which species preferentially adsorb at a given interface is lacking. Experiments to resolve the matter are typically conducted by mixing polymers possessing the same repeat chemistry, but different molecular architecture, e.g., branched or ring and linear polymers [10–14]. To date, there exist limited studies regarding the effect of architecture on the surface segregation of polymer blends composed of the same type of monomer. In our presentation, we discuss our findings following large-scale molecular dynamics simulations of linear-cyclic polymer blend films, which show clear evidence of enhancement of linear polymers at the interface  in agreement with recent experimental results . We also show that the behavior predicted by the self-consistent field theory (SCF), i.e., enhancement of cyclic polymers at the interface , emerges for relatively long chains. Furthermore, a deeper understanding of the role of enthalpic and entropic factors of the interfacial free energy in determining which of the two polymer species in the blend preferentially adsorbs at the interface is achieved by elucidating the underlying microscopic mechanism. At the fundamental level, we try to clarify the way chain length arbitrates the competition between the different packing constraints imposed by the loop and linear geometry of polymers in a blend.
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 Iyer, B. V. S.; Lele, A. K.; Shanbhag, S., Macromolecules 2007, 40, 5995.
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 G. Pellicane, M. Megnidio-Tchoukouegno, G. T. Mola, and M. Tsige, Physical Review E Rapid Communications, 93, 050501 (2016); M. Megnidio-Tchoukouegno, F. M. Gaitho, G. T. Mola, M. Tsige, and G. Pellicane, Fluid Phase Equilibria, http://dx.doi.org/10.1016/j.fluid.2017.02.004 (2017).
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5:15pm - 5:30pmOral
Simulations of Mass and Heat Transport in Cu-Ag Melts Using Embedded-Atom Method Potential
The University of Newcastle, Australia
Mass and heat transfer properties are investigated for liquid Cu-Ag binary alloys over wide temperature and composition ranges by means of equilibrium molecular dynamics computer simulations along with one of the most effective interaction potentials for this system developed in . The kinetic components of the self-diffusion coefficients as well as the collective diffusion coefficients for mass transport Lcc, cross-correlation between mass and heat transport Lcq and heat transport Lqq are estimated from the employed approach. The results obtained can be used to predict the building up temperature and composition gradients at the crystal-melt interface during non-equilibrium solidification of real Cu-Ag alloys.
 P. Williams, Y. Mishin, and J. Hamilton, Modelling Simul. Mater. Sci. Eng., 2006, 14, 817.
5:30pm - 5:45pmOral
On the Oxidation State of Titanium in Titanium Dioxide
National University of Singapore, Singapore
The oxidation state of titanium in titanium dioxide is commonly assumed to be +4. This assumption is used ubiquitously to rationalize phenomena observed with this widely used and technologically important material, although there does not seem to be a direct and independent experimental evidence to support this claim. Furthermore, recent theoretical investigations regularly indicated a charge remainder on Ti in titania compounds, but to the best of our knowledge this has never been investigated in detail.
We present a comprehensive, theoretical electronic structure investigation of Ti ions, titanium dioxide molecules and titania bulk crystals which suggests a lower oxidation state. We analyzed charge density distributions in these systems qualitatively and quantitatively based on results of density functional theory and wave function-based calculations.
We conclude that there is evidence of a significant remaining contribution from valence s and d electrons of Ti, including the presence of a nuclear cusp around the Ti core. The charge corresponding to valence s and d states of Ti amounts to 1 e. The commonly assumed picture may therefore have to be revised.
5:45pm - 6:00pmOral
Materials-By-Design for Carbon Dioxide Capture and Storage
1Boise State University, United States; 2Center for Advanced Energy Studies, United States
Separation and storage of carbon dioxide CO2 from electric power plant flue gases can prevent release of large quantity of CO2 into the atmosphere. This process can reduce CO2 emission and ease global warming, which are both crucial to the environment. The primary candidates for carbon dioxide capture and storage applications are nano-porous solids. A critical challenge in the development of these advanced materials is to understand and control the phenomenon of CO2 sorption hysteresis, whereby the path to adsorption of CO2 molecules by the solid materials differs from that of desorption. We have developed and implemented first-principles modeling approaches, validated with experiments, to design a nano-porous solid material - manganese dioxide octahedral molecular sieve, i.e. OMS-2. Such a porous structure is only stabilized in the presence of cations. The concentration, type and charge of cations have significant effects on CO2 adsorption and diffusion. We found that higher-charge cations have the stronger interaction with the porous surface, causing the worse CO2 uptake capacity. This is the consequence of valence electron donation and molecular orbital hybridization between cation and porous surface. Our presentation will discuss the atomic structure of OMS-2 in the presence of CO2 and CO2-OMS-2 interaction in details. We will also propose three possible mechanisms for CO2 diffusion in the OMS-2, as well as controlling factors of CO2 uptake capacity.
6:00pm - 6:15pmOral
Effect of CO2 Adsorption on the Work Functions of SrTiO3(001) Surfaces
1Entropic Interface Group, Engineering Product Development, Singapore University of Technology and Design, Singapore; 2School of Materials Science and Engineering, Nanyang Technological University, Singapore; 3Department of Physics, University of Oslo, Norway
Perovskites is a promising class of materials for a wide range of electronic and electrochemical applications owing to their stability, low production cost, and a high degree of compositional flexibility. All these features, together with the possibility to adjust the material work function, provide unique possibility to develop inexpesive devices with outstanding catalytic and electronic properties. Work functions of the technologically important perovskite surfaces are well known, however, it is also known that molecular adsorption can affect work function of material surfaces by changing the surface dipole moment. If the change is significant, this phenomenon can potentially affect a catalytic ability of the material and, therefore, has to be taken into account when designing a new perovskite-based catalyst. In this work, we focus on one of the most commonly used perovskite catalyst, SrTiO3, which is effectively used as for photo-splitting of water and photo-degradation of organic pollutants as well as for CO2 photo-reduction. Using first-principle methods, we demonstrate that the CO2 adsorption on both SrTiO3(001) surfaces leads to the formation of the highly stable CO3‑like complexes, increasing the material work function by up to 1.5 and 2.5 eV for TiO2‑ and SrO‑terminated SrTiO3(001) surfaces, respectively. Such offset is sufficient to suppress the photocatalytic ability of TiO2‑terminated SrTiO3(001) and improve the photocatalytic properties of catalytically inert SrO‑terminated SrTiO3(001) surface.
This work is supported by a President Graduate Fellowship from the Ministry of Education of Singapore and Research Council of Norway (Projects 221469 and 250346). We also acknowledge access to high-performance computing resources via NOTUR.