Featured Works

  • J of APPLIED PHYSICS

    114, 164303 (2013)
    Jia-Mian Hu, T. N. Yang, L. Q. Chen,and C. W. Nan
    [Abstract]We study the strain effects on magnetic domain stability and dynamics in nanoscale magnetic thin films using phase-field simulations. Numerous strain-stabilized single-/multi-domain states are discovered, including various magnetic vortices with circular in-plane domains. Furthermore, a strain-domain stability map was constructed, displaying the stable magnetic domain and domain wall structures as a function of biaxial isotropic and anisotropic in-plane strains at room temperature. The present work provides useful guidelines for a precise engineering and experimental observation of domain structures in nanoscale magnetic thin films and a promising scheme towards a low-power and local control over magnetic domain structures.
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  • PHYSICAL REVIEW B

    88, 224105 (2013)
    Eugene A. Eliseev, Sergei V. Kalinin, Yijia Gu,Maya D. Glinchuk,Victoria Khist, Albina Borisevich,Venkatraman Gopalan, Long-Qing Chen, and Anna N. Morozovska
    [Abstract]PHYSICAL REVIEW B We proved the existence of a universal flexoantiferrodistortive coupling as a necessary complement to the well-known flexoelectric coupling. The coupling is universal for all antiferrodistortive systems and can lead to the formation of incommensurate, spatially modulated phases in multiferroics. Our analysis can provide a self-consistent mesoscopic explanation for a broad range of modulated domain structures observed experimentally in multiferroics.
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  • J of APPLIED PHYSICS

    113, 194301 (2013)
    Jia-Mian Hu,T.N.Yang, L.Q.Chen,and C.W.Nan
    [Abstract]We show that, using phase-field simulations, large voltage-driven perpendicular magnetic domain switching can be realized in magnetic-ferroelectric nanoislands with relieved substrate constraint, which is difficult in continuous multiferroic layered thin films due to significant substrate clamping. The as-grown magnetic and ferroelectric domain structures in the heterostructured nanoislands can be tailored by engineering their respective geometric sizes and/or the underlying substrate strain. Influences of the lateral size of the island on the dynamic voltage-driven magnetic domain switching are addressed, whereby an optimum lateral size is identified for illustration.
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  • PHYSICAL REVIEW B

    87, 134102 (2013)
    Anna N. Morozovska,Yijia Gu,Victoria V. Khist,Maya D. Glinchuk,Long-Qing Chen,Venkatraman Gopalan,and Eugene A. Eliseev
    [Abstract]Using Landau–Ginzburg–Devonshire theory and phase-field modeling, we explore the complex interplay between a structural order parameter (oxygen octahedron rotation) and polarization in EuxSr1−xTiO3 thin films. Under a biaxially tensile strain, a low-symmetry monoclinic phase with in-plane ferroelectric polarization is found to be stabilized by antiferrodistortive oxygen octahedra tilts. The monoclinic phase is stable over a wide temperature range. It is characterized by a large number of energetically equivalent polar and structural twin domains.
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  • Acta Materialia

    61 (2013) 7591-7603
    J.J. Wanga, X.Q. Ma, Q. Li, J. Britson, Long-Qing Chen
    [Abstract]An efficient numerical algorithm based on a Fourier spectral iterative perturbation method is proposed to accurately compute the electrostatic fields in three-dimensional (3D) microstructures with arbitrary dielectric inhomogeneity and anisotropy. The method can be conveniently implemented in phase field modeling of microstructure evolution in systems with inhomogeneous dielectric constants as well as inhomogeneous polarization and charge distributions. It is employed to determine the temperature–shape (aspect ratio) phase diagram, domain structures, and domain switching of PbTiO3 nanoparticles using phase field simulations. It is shown that the Curie temperature is enhanced for nanowires and nanorods and reduced for nanodots.
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  • APPLIED PHYSICS L

    103, 142413 (2013)
    J.J. Wang,Jia-Mian Hu, Long-Qing Chen,and Ce-Wen Nan
    [Abstract]Strain effects on domain structures and thermal stability in single-domain magnetic thin films were studied using thermodynamic analysis. The strain-domain structure and stability diagrams were established and compared to several existing experimental results. The structure diagram displays various stable single-domain states under in-plane normal and/or in-plane shear strains by minimizing the free energy density whereas the stability diagram takes into account possible thermal excitations and hence illustrate the thermally stable magnetic single-domain states.
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  • Acta Materialia

    61 (2013) 2909-2918
    F. Xue, J.J. Wang, G.Sheng, Esther Huang, Y. Cao, H.H. Huang,Paul Munroe, R. Mahjoub, Y.L. Li, Valanoor Nagarajan, L.Q. Chen
    [Abstract]Domain stability and structures in Pb(Zr0.3Ti0.7)O3/Pb(Zr0.7Ti0.3)O3 bilayer films under different substrate strains are studied using the phase field method. It is demonstrated that the domain structure of the bilayer film is very different from those of the corresponding single layer films grown on the same silicon substrate with an incoherent interface. Moreover, the predicted rhombohedral domains in the Pb(Zr0.7Ti0.3)O3 layer of the bilayer film have smaller sizes than those in the single layer case. These results are compared with experimental observations and previous thermodynamic analyses.
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  • PHYSICAL REVIEW L

    110, 267601 (2013)
    Yi Wang,Chris Nelson,Alexander Melville,Benjamin Winchester,Shunli Shang,Zi-Kui Liu,Darrell G. Schlom,Xiaoqing Pan,and Long-Qing Chen
    [Abstract]We determined the atomic structures and energies of 109, 180, and 71 domain walls in BiFeO3, combining density functional theory +U calculations and aberration-corrected transmission electron microscopy images. We find a substantial Bi sublattice shift and a rather uniform Fe sublattice across the walls. The calculated wall energies () follow the sequence 109 <180 <71 for the 109, 180, and 71 walls. We attribute the high 71 wall energy to an opposite tilting rotation of the oxygen octahedra and the low 109 wall energy to the opposite twisting rotation of the oxygen octahedra across the domain walls.
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Our Group's Research areas

  • Phase-field method and software development
  • Multiscale modeling integrating density functional theory (DFT) calculations, thermodynamic analysis, and phase-field simulations
  • Domain structures and switching in ferroelectric, ferromagnetic, ferroelastic and multiferroic thin films and devices
  • Interactions between electronic/ionic defects and ferroelectric domains, dielectric degradation and breakdown
  • Ion transport and microstructure evolution in solid electrodes and electrolytes in Li-ion batteries and solid oxide fuel cells (SOFC)
  • Phase-field simulations of structural and diffusional phase transformations, grain growth, and Ostwald ripening in alloys
  • Interactions between dislocations, plasticity, and phase microstructures
  • Co-evolution of microstructure and properties
  • Application of information technology to materials simulation and modeling
  • Integrated computational materials science and engineering

News of Group

IMGThe Third International Conference on Phase-Field Method which will be held during August 26-29,2014.

This is the third international conference on phase-field method following the "First Workshop on Phase-Field Modelling in Materials Science" and the “Second Symposium on Phase-field Modelling in Materials Science”, both at Rolduc Abbey.The purpose of this series of conference is to bring together scientists from universities and research labs, engineers from industry, graduate students, postdocs who are actively involved in the development and applications of phase-field models or who are interested in learning phase-field modelling of microstructure evolution to review the  current status and identify future directions of phase-field method. 

IMGCongratulations Yijia Gu received the Diamond Award of 2013

Yijia Gu, a Ph.D. student working in Long-Qing Chen’s research group has received the Diamond Award for Graduate Excellence in Materials Science from the American Ceramic Society at the Materials Science and Technology Conference in October 2013. Congratulations Yijia!

IMG Congratulations Jiamian Hu received the Diamond Award of 2012

Jiamian Hu, a previous visiting scholar in the Long-Qing Chen research group from Tsinghua University has received the Diamond Award for Graduate Excellence in Materials Science at the Materials Science and Technology Conference in October 2012. Jiamian Hu is a graduate student at Tsinghua University working under the direction of Professor Cewen Nan. Jiamian visited Penn State for sixteen months to work under the direction of Professor Long-Qing Chen. Congratulations Jiamian!