Long-Qing Chen - US grants

9311898 Chen A theoretical investigation will be carried out on the thermodynamics and kinetics of continuous phase transformations and on the possibility of stable nanoscale structures in multicomponent ceramic materials. The main objective is to develop theories and computer simulation techniques for understanding the fundamental thermodynamic and kinetic origins leading to the formation of an important class of self-assembled nanocomposites which resist continuous coarsening. To reach this objective, systematic phase stability analysis and phase diagram calculations for ionic systems with stable nanoscale structures will be performed. The key structural and thermodynamic factors leading to the formation of thermodynamically stable nanoscale phases will be identified. Extensive computer modeling will be conducted of the kinetics of atomic ordering, compositional clustering and microstructural coarsening in systems involving both short-range chemical and long- range Coulomb interactions. A computer simulation technique will be developed which can describe the coarsening dynamics of domains interacting with each other through electric dipole-dipole interactions, elastic interactions and Coulomb interactions. The focus will be on the diffusional transformations in the self- assembled relaxor nanocomposites. The relation of atomic ordering and compositional clustering tendencies to the atomic sizes and charge valences of cations will be investigated through a combination of modern statistical mechanics theory of order- disorder transformations and atomistic computer simulations using shell-model interatomic potentials. %%% This theoretical research grant involves both analytical theory and computer simulation to study the properties of ceramic materials which undergo changes of phase into materials having novel structures. The research will identify the conditions which control the formation of these structures during the phase change. The research is com plicated by the fact that the materials are ionic. This causes additional forces over long distances which are difficult to handle theoretically. However, the results of this work will have important ramifications for understanding and processing these technologically important materials. ***

0073836
Liu

The Department of Materials Science and Engineering at Penn State University develops an integrated computational approach in core subjects of the graduate and upper-undergraduate curricula. The approach is based on new courses on computational thermodynamics, computational kinetics and integrated systems materials design, that integrate fundamental principles and advanced computational tools.

Computer-based educational tools will help students connect abstract thermodynamic concepts with the properties of real world materials and mathematical kinetics with practical materials processing procedures, and thus remove the common perception among students that thermodynamics and kinetics are problematical to learn and difficult to apply in practice.

This award supports theoretical and computational research and education to study the evolution of microsctructure in solids. The main scientific objective of this proposal is to understand the effect of external constraints on phase transformations and microstructure evolution, and the mutual interactions between phase and defect microstructures. The PI will investigate two specific problems using the phase-field approach in combination with mesoscale elasticity theory. The first problem is concerned with phase transformations and domain structure evolution in ferroelectric thin films constrained by a substrate. A phase-field model will be developed for ferroelectric domain evolution in single-crystal films. The model will include long-range elastic and electric dipole-dipole interactions, and the appropriate mechanical and electrical boundary conditions. The initial focus will be on a number of important oxides, PbTiO3, BaTiO3, PbZrxTi1-xO3, for which there have been extensive experimental measurements and theoretical thermodynamic analyses. The PI will systematically investigate the effect of substrate constraints and film thickness on transformation temperatures, volume fractions, and the size of each orientation domain. The focus will be on the temporal evolution of ferroelectric domain structures during nucleation, growth and coarsening, as well as during the domain-wall motion and polarization switching under an electric field. The effect of internal defects, both immobile and diffusive, on domain-wall mobility and ferroelectric/dielectric responses will be studied. The second problem involves the mutual interactions between phase and dislocation microstructures in advanced alloys. Based on recent advances in phase-field modeling of dislocations, a comprehensive model for the simultaneous temporal evolution of phase and dislocation microstructures will be developed, incorporating both elastic anisotropy and elastic inhomogeneity. The PI will study the local phase equilibria, solute segregation kinetics, and nucleation and growth processes around both static and moving dislocations, by varying the solute-solvent size mismatch, elastic inhomogeneity, and the relative solute diffusivity and dislocation mobility. A major effort will be devoted to modeling the influence of solute segregation and second-phase precipitates on the dynamics of both isolated and an ensemble of dislocations under applied stresses. In particular, for a given strain rate, the effect of solute concentration, solute diffusivity, precipitate size and shape, precipitate-precipitate spacing, lattice mismatch, and elastic inhomogeneity, on the critical yield stress of an alloy will be systematically studied. Financial support for two graduate students is requested. The PI will interact closely with experimentalists for validation of theoretical predictions. He also plans collaborations with other theorists to link electronic structure calculations and mesoscale phase-field simulations for modeling phase transformations and microstructure evolution.
The proposed research will impact graduate education in materials, as phase-field simulations of phase transformations and microstructure evolution are being incorporated into a graduate course as part of an educational program on thermodynamics and kinetics. User-friendly software with graphical interfaces will be developed and distributed to other institutions for educational purposes. The proposed project will also result in new computational tools that can potentially be applied to industrially important materials problems as evidenced by the existing collaborations between the PI and industry.
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This award supports theoretical and computational research and education to study the structure of materials on length scales between the atomic and the macroscopic, the microstructure, its role in phase transformations, and its evolution in the presence of external constraints and internal defects. This is a difficult fundamental problem which directly impacts materials processing. The PI will use phase field methods and focus on evolution of domains in ferroelectric materials and the mutual interactions between phase and dislocation microstructures in advanced alloys. Dislocations play an important role in diffusion processes and phase transformations of solids. Ferroelectric materials have applications in sensors and optical components
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This award is made under the Information Technology Research initiative and is funded jointly by the Division of Materials Research and the Advanced Computational Infrastructure Research Division.

This collaborative research project involves two materials scientists, a computer
scientist, a mathematician, and two physicists from academia, industry and a national laboratory. The project is a synergistic effort that leverages the overlapping and complimentary expertise of the researchers in the areas of scalable parallel scientific computing, first-principles and atomistic calculations, computational thermodynamics, mesoscale microstructure evolution, and macroscopic mechanical property modeling. The main objective of the proposal is to develop a set of integrated computational tools to predict the relationships among the chemical, microstructural, and mechanical properties of multicomponent materials using technologically important aluminum-based alloys as model materials. A prototype GRID-enabled software will be developed for multicomponent materials design with efficient information exchange between design stages. Each design stage will incorporate effective algorithms and parallel computing schemes. Four computational components will be integrated, these are: (1) first-principles calculations to determine thermodynamic properties, lattice parameters, and kinetic data of unary, binary and ternary compounds; (2) CALPHAD data optimization computation to extract thermodynamic properties, lattice parameters, and kinetic data of multicomponent systems combining results from first-principles calculations and experimental data; (3) multicomponent phase-field modeling to produce microstructure; and (4) finite element analysis to obtain the mechanical response from the simulated microstructure. The research involves a parallel effort in information technology with two main components: (1) advanced discretization and parallel algorithms, and (2) a software architecture for distributed computing system. The first component includes: (a) a coupling of spectral and finite element approximations, (b) local adaptivity and multi-scale resolution, (c) high order stable semi-implicit in time schemes, (d) parallelization through domain decomposition, and (e) scalable sparse system solvers. The second component involves computational GRID-enabled software for the overall design process; this software architecture enables the use of geographically distributed high performance parallel computing resources to reduce application turnaround time while providing a flexible client-server interface that allows multiple design cycles to proceed.

The research project will be integrated with education and training of graduate students in the broad area of computational science and engineering through the participation of students and the PIs in the "High Performance Computing Graduate Minor" offered through the Institute of High Performance Computing at The Pennsylvania State University. Existing programs at Penn State will be used to integrate undergraduates into the project.
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This award is made under the Information Technology Research initiative and is funded jointly by the Division of Materials Research and the Advanced Computational Infrastructure Research Division.

This collaborative research project involves two materials scientists, a computer
scientist, a mathematician, and two physicists from academia, industry and a national laboratory. The project is a synergistic effort that leverages the overlapping and complimentary expertise of the researchers in the areas of scalable parallel scientific computing, first-principles and atomistic calculations, computational thermodynamics, mesoscale microstructure evolution, and macroscopic mechanical property modeling. The main objective of the proposal is to develop a set of integrated computational tools to predict the relationships among the chemical, microstructural and mechanical properties of multicomponent materials using technologically important aluminum-based alloys as model materials. Prototype GRID-enabled software will be developed for multicomponent materials design. Effective algorithms and parallel computing schemes will be incorporated into the design. The GRID-enabled software allows geographically distributed high performance parallel computing resources to be harnessed bringing greater computational power to bear on a given problem and enabling practical application of these computational tools. The prototype software, with improved predictive power in multicomponent materials design, may enable scientists to develop new materials with unique properties and to tailor existing materials for better performance.

The research project will be integrated with education and training of graduate students in the broad area of computational science and engineering through the participation of students and the PIs in the "High Performance Computing Graduate Minor" offered through the Institute of High Performance Computing at The Pennsylvania State University. Existing programs at Penn State will be used to integrate undergraduates into the project.
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The Industry/University Cooperative Research Center for Computational Materials Design jointly proposed by Penn State and Georgia Tech, aims to substantially impact progress towards systems-based materials design by promoting research programs of interest to both industry and universities, to enhance the infrastructure of computational materials research in the nation, to explore and extend the interface between engineering systems design, information technology and physics-based simulation of process-structure and structure-property relations of materials, to improve the intellectual capacity of the workforce through industrial participation and conduct of high quality research projects, and to develop curriculum in computational and systems design aspects of materials. This will be achieved by developing long-term partnerships among industry, university and other organizations.

The Industry/University Cooperative Research Center for Computational Materials Design joins Penn State and Georgia Tech to substantially impact progress towards systems-based materials design by promoting research programs of interest to both industry and universities, to enhance the infrastructure of computational materials research in the nation, to explore and extend the interface between engineering systems design, information technology and physics-based simulation of process-structure and structure-property relations of materials, to improve the intellectual capacity of the workforce through industrial participation and conduct of high quality research projects, and to develop curriculum in computational and systems design aspects of materials.

NON-TECHNICAL DESCRIPTION: For many years molecular beam epitaxy (MBE) has been used to build layered semiconductor nanostructures atom-by-atom to investigate and improve our understanding of semiconductor physics and create new devices. These devices (which include laser diodes, high-performance transistors, and magnetic field sensors) have advanced healthcare, national security, communications, entertainment, and transportation-resulting in significant improvements in the quality of life for all Americans. Recent progress in research has demonstrated that this same atom-by-atom synthesis technique can be used to build nanostructures of oxides, including ferroelectrics, with comparable nanometer-scale layering control. Since ferroelectric materials exhibit a wide variety of electrical, optical, and electromechanical properties, they are extensively used in healthcare (e.g., medical ultrasound), national defense (e.g., night vision and sonar systems), and communications (e.g., miniature capacitors for cell phones and computers). The ability to customize the layering of ferroelectric materials at the atomic-layer level and strain them opens exciting possibilities to dramatically enhance their properties. The improved understanding gained via this research will be applied to the development of improved optical and acoustic devices. Future scientists in a highly interdisciplinary research environment in a technologically significant area of national importance will be trained and educated within this program. Professors from Pennsylvania State University, University of Wisconsin, University of Michigan and Rutgers University will run hands-on workshops during the summers at each of the campuses involved in this research team to expose K-12 students to the thrill of science.

TECHNICAL DETAILS: The technical objective is to understand the fundamental science underlying the electric, magnetic, and optical responses of strained nanoscale ferroelectrics and multiferroics. An integrated theoretical and experimental effort will be taken. Specifically, "first-principles effective Hamiltonian" approaches based on lattice Wannier functions and Landau-Ginzburg type phenomenological methods will be used to identify ferroelectric and multiferroic materials and heterostructures in which large enhancements in properties are expected with strain. Films will be grown by MBE and laser-MBE, patterned by focused ion beams, and characterized using a combination of x ray diffraction, analytical and transmission electron microscopy, Raman spectroscopy, second harmonic generation, and ferroelectric measurements, all as a function of temperature. Strain is utilized in many semiconductor device structures to improve the transport properties of thin semiconductor layers. Within this project, it will be used to enhance the properties of ferroelectrics. Ferroelectrics are very sensitive to strain and a distinct advantage of thin ferroelectric materials over their bulk counterparts is that they may be strained well beyond where their bulk counterparts would crack. For nanoscale ferroelectrics, huge strains become accessible. This feature combined with the ability to precisely integrate and engineer oxides at the atomic level provides a means to investigate, develop, and exploit the properties of oxides for optical modulators, two-dimensional photonic bandgap structures, and phonon-confining piezoelectric structures relevant to the long-term realization of a phonon laser.

Florida Institute of Technology and Penn State University in the US team up with Ulm University and the Technical University in Dresden, Germany, to address the fundamental problem of phase coarsening. The primary goal of this project is to understand the kinetics of phase coarsening at ultra-high (> 90%) volume fractions, which are expected to be fundamentally different from the classical Lifshitz/Slyozov/Wagner kinetics at vanishing volume fractions (~0%) as well as from the kinetics of grain growth in single-phase systems (100%). The team conducts a combination of theoretical, computational and experimental studies. Specific research activities include: (1) developing a new theory for phase coarsening at ultra-high volume fractions; (2) conducting large-scale phase-field simulations of complex three-dimensional (3D) microstructural evolution that will yield important information such as coarsening rates, the temporal evolution of particle-size distributions and correlation functions, etc.; (3) measuring the 3D coarsening behavior of real two-phase systems in situ using time-resolved x-ray microtomography; and (4) carrying out quantitative comparisons between theory, simulation and experiments. A quantitative understanding of 3D phase coarsening kinetics is crucial to the optimization of processing conditions for controlling the final structure and properties of multiphase materials. The volume fraction of the coarsening phase is a critical factor in determining the coarsening kinetics. Due to the daunting theoretical and experimental challenges posed by complex microstructures at high-volume fractions of the coarsening phase, existing theoretical work has been limited to low volume fractions (< ~30%), and most experimental characterization has been carried out solely in two dimensions (2D) by metallographic sectioning. However, recent advances in theoretical modeling, computational simulation and 3D microstructural characterization offer an unprecedented opportunity to overcome the difficulties inherent in the study of coarsening at ultra-high volume fractions. The specific thrusts of this project therefore lie in improving our understanding of fundamental materials phenomena, in discovering new kinetics associated with complex microstructures, and in advancing the state of the art of simulation and experimental tools for 3D microstructural evolution and properties.
Students and junior researchers participating in this project travel to the counterpart institutions across the Atlantic in order to immerse themselves in theoretical, computational and experimental studies of 3-D microstructural evolution. Via the student exchange program, these young researchers profit from the opportunity to develop skills that complement the intensive training in theory, simulation, or experiment that they receive at their home institutions, resulting in a multifaceted educational experience.
This award is co-funded by the NSF Office of International Science and Engineering.

Proposal #: CNS 08-21527
PI(s): Raghavan, Padma
Chen, Long-Quing; Hudson, Peter J.; Kandemir, Mahmut T.; Smith, Brian K.
Institution: Pennsylvania State University
University Park, PA 16802-700
Title: MRI/Acq.: Acq.of A Scalable Instrument for Discovery through Computing
MRI Acquisition of a Scalable Instrument for Discovery through Computing

This award from the Major Research Instrumentation Program (MRI)
provides funds for the acquisition of a terascale advanced computing
instrument at the Pennsylvania State University. The instrument
will enable researchers from seven disciplines (biological, materials
and social sciences, computer and information science, engineering,
education, and geosciences), to perform virtual experiments toward
discovery and design through computing. Research projects concern:
predictive network modeling of infectious disease dynamics, designing
new piezoelectric materials, designing next-generation chip
multiprocessors, modeling human interactions to promote learning
in virtual communities, and the development of a critical zone
environmental observatory. Despite their diversity, these projects
share computational scalability challenges to be addressed for
enabling scientific advances that often depend on solving large
problems representing a sufficient level of detail and complexity.
The instrument will form the core of a multidisciplinary collaborative
environment to enable transformative approaches to address the
challenges of scaling at multiple levels. It will support a set of
integrated research, education, training, and outreach activities
to: (i) enable collaborative scaling across projects through the
transfer of scaling approaches from one domain into another, while
addressing algorithmic, system, or instrument scaling challenges
within individual projects, (ii) promote technology-transfer through
industrial partnerships, and (iii) grow and enhance the diversity
of the limited computational science talent pool.

This MWN research focuses on new insights into the fundamental nature of ferroelectric domain walls developed by this joint US/Ukraine team over the past two years. In particular, the team leverages the comprehensive theory, simulation and advanced experimental framework they have developed for quantitative piezoelectric force microscopy (PFM). Using this framework, they have discovered unexpected broadening of ferroelectric domain walls over tens of nanometers. Analytical theory and phase field modeling, predicts that even a few nanometers of broadening can dramatically change the macroscale properties such as threshold fields for wall motion, by many orders of magnitude. The team predicts unusual magnetic-like domain walls in ferroelectrics. Such walls can be engineered to be extremely broad, (100's nm), and their dynamical properties under electric fields, and hence their impact on macroscale properties are presently unexplored. Using Scanning Spectroscopy Piezoelectric Force Microscopy (SSPFM), and optical second harmonic generation-near field scanning optical microscopy (SHG-NSOM), the team is exploring this mysterious new world of domain walls. Broadly speaking, the US team (Penn State and Oak Ridge National Labs) focuses on the experimental and phase-field simulations of such ferroelectric walls, while the Ukranian team (National Academy of Sciences, Ukraine) is developing the theoretical framework.

The development of quantitative PFM and SHG-NSOM imaging techniques that combine theory, numerical simulations and cutting-edge experimental techniques are expected to have a much broader impact that extends beyond ferroelectrics, to other fields of materials science, chemistry and life sciences. This US/Ukranian team is an excellent example of a genuine international collaboration that started rather spontaneously a few years ago between the PIs, and has been very productive. This proposal will provide funds to energize and sustain this spontaneous effort by supporting undergraduate and graduate students to work and collaborate in a global context, support extended visits across the Atlantic by PIs and students alike, further interactions between a university (Penn State), a national lab (Oak-Ridge National Lab) and a national academy (NAS-Ukraine), support organization of an annual international workshop on Piezoelectric Force Microscopy and summer workshops in nonlinear optical microscopy, and provide research opportunities for women and underrepresented groups.

This MWN award is co-funded by DMR-EPM, DMR-OSP, and OISE Eurasia Region.

Center for Computational Materials Design (CCMD)

IIP-1034965 Pennsylvania State University (PSU)
IIP-1034968 Georgia Tech (GT)

This is a proposal to renew the Center for Computational Materials Design (CCMD), an I/UCRC center that was created in 2005. The lead institution is Pennsylvania State University, and the research partner is Georgia Tech. The main research mission of the CCMD is to develop simulation tools and methods to support materials design decisions and novel methods for collaborative, decision-based systems robust design of materials.

The intellectual merit of CCMD is based on the integration of multiscale, interdisciplinary computational expertise at PSU and GT. CCMD provides leadership in articulating the importance of integrated design of materials and products to industry and the broad profession of materials engineering; and is developing new methods and algorithms for concurrent design of components and materials.

CCMD has operated successfully in Phase I, and has helped develop a partnership amongst academe, industry and national laboratories. Based on feedback received from the various members, CCMD has outlined in the renewal proposal research thrusts and initiatives for Phase II; and has also identified gaps that will be addressed as research opportunities in Phase II.

CCMD will have a large impact on how industry addresses material selection and development. The expanded university/industry interaction of this multi-university center offers all participants a broader view of material design activities in all sectors. CCMD contributes to US competitiveness in computational materials design by educating new generations of students who have valuable perspectives on fundamental modeling and simulation methods, as well as industry-relevant design integration and materials development. CCMD participates in programs at PSU and GT that support K-12 STEM issues, women and underrepresented groups, undergraduate students, and high school teachers. CCMD plans to disseminate research results via papers, conferences and the CCMD website.

TECHNICAL SUMMARY

This award supports theoretical and computational research on electro-magneto-mechanical couplings in ferroelectric and multiferroic nanostructures. Ferroelectrics and multiferroics are multi-functional materials that have many applications in devices such as actuators, sensors, and memory storage. The main objective of the project is to fundamentally understand the roles of mechanical and electrical boundary conditions in their ferroic responses. The focus is on the piezoelectric responses of nanoferroelectrics and the magnetoelectric coupling of self-assembled epitaxial nanocomposites of ferroelectric and ferromagnetic crystals. The phase-field approach will be employed in combination with mesoscale elasticity, electrostatic theory, and micromagnetics. The particular goals of the project are as follows:

(1) The PI will develop and implement efficient numerical algorithms based on the spectral method for solving the phase-field, mechanical, electrostatic, and magnetostatic equations while taking into the appropriate electric and mechanical boundary conditions.

(2) The PI will investigate the dependence of piezoelectric responses of ferroelectric nanostructures on substrate constraints as well as on the inhomogeneous stress distributions within a nanostructure due to presence of defects such as dislocations.

(3) The PI will study the correlation between the multiferroic nanocomposite microstructure and the magnitude of magnetoelectric coupling effect.

This research program involves active collaborations with applied mathematicians on the implementation of advanced numerical algorithms and with experimentalists on experimental validation of computational predictions and findings. The research under this award is expected to (i) significantly contribute to the fundamental understanding of the piezoelectric responses of nanoferroelectrics and magnetoelectric coupling effect of multiferroic nanocomposites, (ii) yield new phase-field formulations for modeling multiferroic domain structures, and (iii) produce advanced numerical algorithms for solving phase-field equations involving non-periodic boundary conditions.

This award supports training graduate as well as undergraduate students through thesis and summer research. Software tools developed from the project will be incorporated into two graduate courses and an undergraduate course. The research findings will be disseminated to a wide audience through archival publications and conferences, review and overview papers, and active participation and lectures at interdisciplinary workshops.

NON-TECHNICAL SUMMARY

This award supports theoretical and computational research on the properties and functionalities of ferroelectric and multiferroic oxides. Ferroelectrics and multiferroics are multi-functional materials that can produce two or more different types of responses when they are subjected to an external field. They have many potential applications in devices such as actuators, sensors, and computer memory storage. For example, a ferroelectric crystal can change both its shape and electric polarization when it is subject to an external mechanical stress. Electric polarization results when the negative electronic charge distribution is shifted from the positive charge distribution of the atomic nuclei in a crystal. In a multiferroic material, the magnitude and direction of both the magnetization and electric polarization can be altered by externally applying either an electric or a magnetic field.

The research program has two main thrusts: The PI will investigate the so-called "piezoelectric response", which is related to the magnitude of the change in electric polarization under a mechanical stress or the degree of crystal shape deformation under an electric field. These effects will be examined in bulk ferroelectrics as well as in tiny structures of sizes that are approximately one billionth the size of the human hair. Secondly, the PI will investigate the so-called "magnetoelectric" coupling, which is related to the change in electric polarization under an applied magnetic field or the change in magnetization under an applied electric field. The PI will develop and apply various computational tools in these investigations. The overall goal is to optimize the multi-functionalities of such materials through computer simulations. The research program involves active collaborations with applied mathematicians on the implementation of advanced numerical algorithms and with experimentalists on experimental validation of computational predictions and findings.

The project will contribute to human resource development by training graduate as well as undergraduate students through thesis and summer research. Software tools developed from the project will be incorporated into two graduate courses and an undergraduate course. The research findings will be disseminated to a wide audience through archival publications and conferences, review and overview papers, and active participation and lectures at interdisciplinary workshops.

TECHNICAL SUMMARY: The functional properties of ferroelectrics and ferroelastics, materials with built-in polarization and elastic distortion states in their crystal structure, respectively, are typically reliant on their response under uniform spatial elastic and electric fields, e.g., switching, piezoelectric, and electro-optic responses. There is also a rich range of ferroic phenomena arising under gradient fields, which receive much less attention. This project is based on two new discoveries/ideas initiated by the US/Ukraine team: New highly tunable metastable states and roto-flexo phenomena. Strong gradient fields created at and in the proximity of domain walls can result in local phase transitions that lead to new bulk polar phases not normally expected in classic textbook ferroelectrics, and even in non-polar ferroelastics. In all oxide interfaces with oxygen octahedral tilts, the creation of a polarization (up to 1-10 microC/cm2) is predicted through a rotostriction-flexoelectric product effect that can significantly impact the interface charge transport. Using optical second harmonic generation microscopy, Raman microscopy, scanning probe microscopy, nanoscale X-ray diffraction imaging, z-contrast scanning transmission electron microscopy, analytical theory, phase-field modeling, and first principles theory, this collaborative team explores these new phenomena. Broadly speaking, the US team (Pennsylvania State University, Oak Ridge National Labs, Argonne National Labs) conducts experimental research and performs phase-field simulations, and the Ukrainian team (National Academy of Sciences, Ukraine) focuses on developing the theoretical framework.

NON-TECHNICAL SUMMARY: This project can potentially lead to new highly tunable, large piezoelectric response lead-free materials useful for precision motion and sensors. Gradient couplings at interfaces can lead to two-dimensional electron gas systems of great current interest for next generation high-speed transistors. This project also develops cutting-edge quantitative microscopy tools and advances theoretical modeling by simulating flexoelectric and other gradient effects. The NSF award provides funds to energize and sustain an international research team, which started in 2007. It funds undergraduate and graduate students to work and collaborate in a global context, supports extended visits across the Atlantic by PIs and students, furthers interactions between a university (Penn State), national labs (Oak Ridge and Argonne) and international collaborators (NAS-Ukraine), supports outreach activities through K-12, and provides research opportunities for women and underrepresented groups.

This project is supported by the Electronic and Photonic Materials program and Office of Special Programs, Division of Materials Research.

The research objective of this grant is to fundamentally understand the thermodynamic driving forces and kinetic mechanisms leading to the formation of lithium metal dendrites in Li-batteries. One of the most significant challenges for Li-ion battery design is the prevention of Li-dendrite growth, which would allow faster charging for current Li-ion battery technology and the use of Li metal anodes for future "beyond Li-ion batteries." A computational model based on the phase-field method will be developed to predict the conditions for dendrite growth and morphological changes with input thermodynamic, mechanical and kinetic parameters from atomistic/first principles calculations and experimental measurements. The proposed model will be based on a nonlinear kinetics in which the dependence of the rate of changes of a phase-field parameter is nonlinear with respect to the thermodynamic driving force, and hence it is applicable to modeling the microstructure evolution under large overpotentials or high charging rates. One of the key parameters is the Li metal/electrolyte interface energy, which will be directly computed by connecting DFT calculations and liquid thermodynamic data. This three-year grant will lead to (1) fundamental understanding of the transport and chemical kinetics of dendrite formation and growth and their relationships to their solid electrolyte interphase (SEI) film properties and (2) the development of a physics-based microstructure evolution model that does not rely on non-transferable fitting parameters to predict the conditions for dendrite formation and growth morphology. The ultimate goal for this work is to eliminate the formation-- or at least to limit the growth-- of dendrites on Li metal electrodes.

Dendrite formation is the primary degradation and failure mechanism and a safety concern in Li batteries, either because dendrite pieces lose electrical contact with the rest of the Li electrode or because growing dendrites penetrate the separator and lead to short circuits. The fundamental understanding achieved from this research program is expected to contribute to the Li ion battery safety improvement, a critical need for the near-term development of hybrid and electric vehicles. The planned research, both the methodology and the actual results, are designed to make significant contributions to new battery technology by providing important fundamental information about electrode materials behavior under various electrochemical conditions. The direct involvement of GM scientists provides an important avenue for disseminating the knowledge generated from this project. The primary research results will be shared with the public on-line to the public at http://lithiumbatteryresearch.com/ in addition to peer-reviewed publication and conference proceedings. The graduate student and postdoc supported by this project will spend extended periods of time in an industrial environment, which will provide an important added dimension to their education. Both of these individuals will thus be very well positioned for future work in battery-related fields. In addition, undergraduate students will be integral to the program via Penn State's MURE (Minority Undergraduate Research Experience) programs and senior thesis projects in the Department of Materials Science and Engineering at Penn State.

Technical Description: Complex oxides have been fertile ground for new discoveries, due particularly to their wide-ranging electronic, optical, and magnetic properties. Interfaces between complex oxides and related materials create juxtapositions between different symmetries and ordered states, and it has become clear that these interfaces are new materials in their own right and lead to dramatically different properties from those in bulk. This project focuses on an iterative cooperation between forefront theory and experiment that determines the fundamental principles controlling new physical phenomena at oxide interfaces, uses these principles to design couplings between multiple orders at interfaces to generate new functionalities, and experimentally synthesizes and investigates designed interfacial materials for novel electronic devices. These atomic-scale interfacial materials can lead to, for example, new classes of electric-field controllable electronic and magnetic phenomena, and enable the development of new technologically important devices that exploit these couplings. Using a predictive theory and modeling, and feedback to theory from experiments, the research team aims to design, understand, and synthesize novel oxide hetero-interfaces that have unique properties not presently available.

Non-technical Description: New approaches to the discovery of materials displaying novel properties are critical for the continued scientific progress in condensed matter science and applications. This project addresses this need with a focus on "oxide interfacial materials," those formed at and near the atomically abrupt boundary between two oxygen-based materials, each of which can exhibit a stunning array of phenomena such as magnetism, piezoelectric behavior, superconductivity, and structural ordering. At the interface, interactions between these functionalities give rise to unexplored nanoscale behaviors. These new interfacial materials are some of the most promising in which to realize new phenomena that will challenge our current understanding, and that will develop new electronic device directions to address our society's technology needs. The project brings a broad educational experience to all students, interacting with faculty members of this research team at five universities, working with scientists at National Laboratories and international institutions, and participating in outreach activities. The faculty and graduate students work with secondary school teachers from the US and Puerto Rico to develop classroom material based on their materials genome learning/research experience.

NONTECHNICAL SUMMARY
This award supports theoretical research and computational modeling, and education with an aim to better understand ferroelectrics, which are multifunctional materials that have many uses, including actuators, sensors, memory storage, and microelectromechanical systems. These materials can not only produce electric signals under an applied electric field or a macroscopic shape deformation under an applied mechanical stress field but can also produce electric signals in response to an applied mechanical stress or a shape deformation in response to an applied electric field. There have been extensive studies on the couplings among electric signals, electric fields, homogeneous mechanical loads, temperature, and homogeneous shape deformations, and the basic science of how a homogeneous shape deformation affects the electric properties of ferroelectrics, characterized by the "piezoelectric effect," is reasonably well understood. In this project, the PI will focus on understanding how an inhomogeneous stress or shape deformation affects the multifunctional properties of ferroelectrics, through the "flexoelectric effect." Effort will be devoted to developing efficient computational methods and employing them to model, predict, and understand internal, nanoscale inhomogeneous structures and properties of ferroelectric materials under the influence of the flexoelectric effect. The computational research will be carried out in close collaboration with numerous experimental groups, computational physicists, and applied mathematicians. The fundamental understanding achieved and the computational tools developed in this project should provide guidance to develop material systems that can exploit the flexoelectric effect that exists in all materials. The proposed research is expected to contribute to graduate education in materials as phase-field simulations of phase transformations and microstructure evolution are being incorporated into graduate courses at Penn State. In particular, user-friendly graphical interfaces for a number of applications of the phase-field models have been developed under prior NSF support. The software has been employed in two graduate courses and one undergraduate course. In addition, it has been used in summer short courses on computational thermodynamics and kinetics of phase transformations, which were offered to research scientists from national labs, engineers from industry, and professors and students from academia. This project will provide new computational tools to illustrate how materials properties may be modified through the flexoelectric effect. The PI will involve undergraduate students in the research by participating in a number of programs at Penn State including senior thesis projects and the Minority Undergraduate Research Experience program.


TECHNICAL SUMMARY
Ferroelectrics are a class of materials in which a spontaneous electric polarization develops below their paraelectric to ferroelectric phase transition temperatures. The spontaneous polarization direction can be reoriented among crystallographically defined orientations in a single crystal by an electric field. Very often a spontaneous strain arising from the crystal structure change at the ferroelectric transition accompanies the appearance of spontaneous polarization. So, the state of a ferroelectric crystal can generally be characterized macroscopically by two order parameters, polarization and strain. It is the coupling between the order parameters, polarization and strain, and the thermodynamic variables such as temperature, stress, and electric field that leads to the multifunctionality of a ferroelectric crystal ranging from dielectric, piezoelectric to pyroelectric properties, and thus to many applications in a wide variety of electronic devices, including capacitors, actuators, nonvolatile memories, and microelectromechanical systems. Although the thermodynamics of these couplings has been well established, the coupling among order parameters and their gradients is much less well understood. The main goal of this proposed program is to fundamentally understand the role of the flexoelectric effect, the coupling between polarization and the gradient of strain in the ferroelectricity of a crystal, in domain structures, polarization distributions across domain walls, and domain switching. There is sufficient evidence that the flexoelectric effect, which is small and generally ignored in macroscopic systems, may become significant or even dominant with decreasing size approaching nanostructures, particularly in ferroelectric materials which exhibit strong dielectric properties. The PI plans to employ a phase-field modeling approach integrated with mesoscale elasticity and electrostatic theory. The main objectives of this proposal are: (1) to develop a phase-field model of ferroelectric domain structures and switching incorporating flexoelectric contributions, (2) to study whether the flexoelectric contribution can significantly modify the properties of a ferroelectric domain wall and to discover potentially new domain wall features induced by the flexoelectric effect, (3) to investigate the role of the flexoelectric contribution to the polarization distribution and thus to domain structure in thin films, and (4) to investigate the flexoelectric response of ferroelectric thin films under a local mechanical force and explore the possibility of mechanical switching of ferroelectric polarization. The proposed research is expected to: (1) yield a phase-field formulation for modeling flexoelectric response of ferroelectrics, (2) significantly contribute to the fundamental understanding of the roles of flexoelectric effect in ferroelectric properties including domain wall structures, polarization distribution, and switching, and (3) produce advanced numerical algorithms based on the spectral method for solving phase-field equations involving domain wall anisotropy and flexoelectricity. The project will contribute to human resource development by training both graduate and undergraduate students through undergraduate thesis and summer research. The research findings will be disseminated to a wide audience through archival publications and conferences, review papers, and active participation and lectures at workshops and conferences. Finally, the PI will actively pursue collaborations with industry and national labs such as Los Alamos, Argonne, Oak Ridge, and the industrial members associated with the Center for Dielectrics and Piezoelectrics (CDP) at North Carolina State University and Penn State to provide internship opportunities for students involved in the project.

NON-TECHNICAL DESCRIPTION: Materials with a particular crystalline arrangement of atoms, known as perovskite, have played important roles in applications ranging from electronic and magnetic devices to micro-machined actuators and sensors. Some of the most interesting phenomena arise at interfaces between these and other materials, where the atomic and structural aspects combine to form new materials in their own right. The main goal of this research is the discovery of a new class of interface materials based on antiperovskites. These antiperovskites exchange the atomic positions of the more common perovskites, creating unique, wide-ranging properties different from the parent materials. Interfaces between these two 'anti'-structures create unexplored fundamental opportunities for materials design. This research will discover the fundamental principles controlling these new materials systems, develop atomic-scale design principles, and create and explore these interfaces for potential applications in electronic, magnetic, and quantum-controlled devices.

TECHNICAL DESCRIPTION: Complex perovskite materials have been fertile ground for new discoveries, due particularly to their wide-ranging structural, electronic, optical, and magnetic properties. Interfaces between perovskites create juxtapositions between different symmetries and ordered states, and it has become clear that these interfaces are new materials in their own right, with inherently multiple length-scale distortions near the interface that lead to rotations, deformations, and electronic and structural orderings dramatically different from those in bulk. The main goal of this research is the discovery of a new class of interface materials based on antiperovskites. Antiperovskites have the perovskite structure, but cation and anion positions are interchanged, resulting in unique, wide-ranging properties different from perovskites. Interfaces between these two 'anti'-structures create unexplored fundamental opportunities for materials design. The fundamental principles controlling new physical phenomena at these interfaces will be determined, and the principles used to design couplings between multiple orders at interfaces to generate new functionalities. This research is aimed at developing atomic scale design principles for antiperovskite heterointerfaces, constructing databases of the stable interface structures, and developing antiperovskite heterostructures with scientifically important and technologically transformative structural, electronic, and magnetic properties. The project implements an integrated effort of theory, materials synthesis, structural, electronic, and magnetic characterization. The research will use an iterative approach, where feedback from experimental measurements of interfacial structure and electric and magnetic order is used to refine theoretical parameters and approximations. This iterative approach will develop a fundamental understanding of the interface atomic structure and bonding between disparate materials, and how it creates new interfacial spin order and electronic configurations. These atomic-scale interface materials will lead to new classes of controllable electronic and magnetic phenomena, and new growth approaches that will make possible heteroepitaxy of other materials systems with large disparity in structure and chemical bonding. The predictive theory and modeling, with feedback to theory from materials growth, and from structural, electronic, and transport characterization, will produce hetero-interfaces that have unique properties not presently available.