Engineering topics
Publications and source records attributed to Ozolins, Vidvuds.
Thermoelectric materials based on tetrahedrite structures for thermoelectric devices and methods for producing thermoelectric materials and devices are disclosed.
The primary goal of this program is to develop computational tools and methodology for enabling a shift from empirical trial-and-error driven materials discovery towards data and information technology driven design of materials with targeted functional properties. Both thermodynamic and kinetic factors need to be taken into account when designing new materials. Thermodynamics sets the necessary-but-not-sufficient conditions for the suitability of a particular material in a given application, while the kinetics controls the rates of microscopic processes and hence the performance in energy applications (e.g., power in energy storage, conversion efficiencies in solar cells and thermoelectrics, chemical activity in catalysis). The complexity of these phenomena makes computational design difficult, not least due to the lack of suitable theoretical methods and computational tools. To address these needs, we develop systematic, quantitatively accurate first-principles methods to address two important problems: (i) predict and optimize the thermodynamics of materials over a large composition and structure space, and (ii) model kinetic processes such as mass and heat transport in crystalline solids under non-equilibrium conditions. These tasks are addressed by combining high-throughput computation with automatic construction of accurate lattice models using mathematically rigorous methods of information theory, such as compressive sensing and Bayesian inference.
Correction for ‘High thermoelectric performance in complex phosphides enabled by stereochemically active lone pair electrons’ by Xingchen Shen et al. , J. Mater. Chem. A , 2018, 6 , 24877–24884.
An alternative strategy to create optimum band shape for superior thermoelectric performance by utilizing stereochemically active lone pair electrons is proposed, which has been demonstrated in the Ag 6 Ge 10(1 -x ) Ga 10 x P 12 .
Abstract not provided
Thermoelectric materials based on tetrahedrite structures for thermoelectric devices and methods for producing thermoelectric materials and devices are disclosed.
The short charging times and high power capabilities associated with capacitive energy storage make this approach an attractive alternative to batteries. One limitation of electrochemical capacitors is their low energy density and for this reason, there is widespread interest in pseudocapacitive materials that use Faradaic reactions to store charge. One candidate pseudocapacitive material is orthorhombic MoO3 (α-MoO3), a layered compound with a high theoretical capacity for lithium (279 mA h g-1 or 1,005 C g-1). Here, we report on the properties of reduced α-MoO3-x(R-MoO3-x) and compare it with fully oxidized α-MoO3 (F-MoO3). The introduction of oxygen vacancies leads to a larger interlayer spacing that promotes faster charge storage kinetics and enables the α-MoO3 structure to be retained during the insertion and removal of Li ions. The higher specific capacity of the R-MoO3-x is attributed to the reversible formation of a significant amount of Mo4+ following lithiation. This study underscores the potential importance of incorporating oxygen vacancies into transition metal oxides as a strategy for increasing the charge storage kinetics of redox-active materials.
The objective of the proposed program is to discover novel mixed hydrides for hydrogen storage, which enable the DOE 2010 system-level goals. Our goal is to find a material that desorbs 8.5 wt.% H 2 or more at temperatures below 85°C. The research program will combine first-principles calculations of reaction thermodynamics and kinetics with material and catalyst synthesis, testing, and characterization. We will combine materials from distinct categories (e.g., chemical and complex hydrides) to form novel multicomponent reactions. Systems to be studied include mixtures of complex hydrides and chemical hydrides [e.g. LiNH 2+ NH 3 BH 3 ] and nitrogen-hydrogen based borohydrides [e.g. Al(BH 4 ) 3 (NH 3 ) 3 ]. The 2010 and 2015 FreedomCAR/DOE targets for hydrogen storage systems are very challenging, and cannot be met with existing materials. The vast majority of the work to date has delineated materials into various classes, e.g., complex and metal hydrides, chemical hydrides, and sorbents. However, very recent studies indicate that mixtures of storage materials, particularly mixtures between various classes, hold promise to achieve technological attributes that materials within an individual class cannot reach. Our project involves a systematic, rational approach to designing novel multicomponent mixtures of materials with fast hydrogenation/dehydrogenation kinetics and favorable thermodynamics using a combination of state-of-the-art scientific computing and experimentation. We will use the accurate predictive power of first-principles modeling to understand the thermodynamic and microscopic kinetic processes involved in hydrogen release and uptake and to design new material/catalyst systems with improved properties. Detailed characterization and atomic-scale catalysis experiments will elucidate the effect of dopants and nanoscale catalysts in achieving fast kinetics and reversibility. And, state-of-the-art storage experiments will give key storage attributes of the investigated reactions, validate computational predictions, and help guide and improve computational methods. In sum, our approach involves a powerful blend of: 1) H2 Storage measurements and characterization, 2) State-of-the-art computational modeling, 3) Detailed catalysis experiments, 4) In-depth automotive perspective.
Molecularly Engineered Energy Materials (MEEM) was established as an interdisciplinary cutting-edge UCLA-based research center uniquely equipped to attack the challenge of rationally designing, synthesizing and testing revolutionary new energy materials. Our mission was to achieve transformational improvements in the performance of materials via controlling the nano-and mesoscale structure using selectively designed, earth-abundant, inexpensive molecular building blocks. MEEM has focused on materials that are inherently abundant, can be easily assembled from intelligently designed building blocks (molecules, nanoparticles), and have the potential to deliver transformative economic benefits in comparison with the current crystalline-and polycrystalline-based energy technologies. MEEM addressed basic science issues related to the fundamental mechanisms of carrier generation, energy conversion, as well as transport and storage of charge and mass in tunable, architectonically complex materials. Fundamental understanding of these processes will enable rational design, efficient synthesis and effective deployment of novel three-dimensional material architectures for energy applications. Three interrelated research directions were initially identified where these novel architectures hold great promise for high-reward research: solar energy generation, electrochemical energy storage, and materials for CO 2 capture. Of these, the first two remained throughout the project performance period, while carbon capture was been phased out in consultation and with approval from BES program manager.
Here, we analyze thermodynamic stability and decomposition pathways of LiBH 4 nanoclusters using grand-canonical free-energy minimization based on total energies and vibrational frequencies obtained from density-functional theory (DFT) calculations. We consider (LiBH 4 ) n nanoclusters with n = 2 to 12 as reactants, while the possible products include (Li) n , (B) n , (LiB) n , (LiH) n , and Li 2 B n H n ; off-stoichiometric LinBnHm (m ≤ 4n) clusters were considered for n = 2, 3, and 6. Cluster ground-state configurations have been predicted using prototype electrostatic ground-state (PEGS) and genetic algorithm (GA) based structural optimizations. Free-energy calculations show hydrogen release pathways markedly differ from those in bulk LiBH 4 . While experiments have found that the bulk material decomposes into LiH and B, with Li 2 B 12 H 12 as a kinetically inhibited intermediate phase, (LiBH 4 ) n nanoclusters with n ≤ 12 are predicted to decompose into mixed Li n B n clusters via a series of intermediate clusters of Li n B n H m (m ≤ 4n). The calculated pressure-composition isotherms and temperature-pressure isobars exhibit sloping plateaus due to finite size effects on reaction thermodynamics. Generally, decomposition temperatures of free-standing clusters are found to increase with decreasing cluster size due to thermodynamic destabilization of reaction products.
Abstract not provided
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First-principles prediction of lattice thermal conductivity K L of strongly anharmonic crystals is a long-standing challenge in solid state physics. Using recent advances in information science, we propose a systematic and rigorous approach to this problem, compressive sensing lattice dynamics (CSLD). Compressive sensing is used to select the physically important terms in the lattice dynamics model and determine their values in one shot. Non-intuitively, high accuracy is achieved when the model is trained on first-principles forces in quasi-random atomic configurations. The method is demonstrated for Si, NaCl, and Cu 12 Sb 4 S 13 , an earth-abundant thermoelectric with strong phononphonon interactions that limit the room-temperature K L to values near the amorphous limit.
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