Lattice dynamics of hybrid improper ferroelectric (Ca,Sr)3Ti2O7

ORAL

Abstract

In hybrid improper ferroelectric (Ca,Sr)3Ti2O7, the anharmonic coupling between a stable zone-center polar phonon mode and two unstable zone-boundary non-polar modes, and quasi-2D behavior of c-polarized acoustic modes are theoretically proposed but remain to be experimentally validated. We have performed comprehensive T-dependent single-crystal diffraction, calorimetry, and phonon measurements in (Ca,Sr)3Ti2O7 for x = 0, 0.6, and 0.9, including the behavior across the ferroelectric transition Tc. We also performed first-principles phonon simulations. Our results revealed a strong broadening but little shifting of mean phonon energy on heating across Tc. Among two unstable modes, rotational mode remains robust, but the tilt mode shows substantial softening on heating, consistent with previous studies. However, contrary to previous simulations, our momentum and energy resolved inelastic x-ray scattering measurements did not show a quadratic dispersion of acoustic modes, theoretically associated with a quasi-2D character. Our detailed lattice dynamics study enables to benchmark simulations of anharmonic phonons and associated thermodynamic properties such as thermal expansion and thermal conductivity.

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Presenters

  • Dipanshu Bansal

    Indian Institute of Technology Bombay, Mechanical Engineering, Indian Institute of Technology Bombay, Department of Mechanical Engineering & Materials Science, Duke University

Authors

  • Dipanshu Bansal

    Indian Institute of Technology Bombay, Mechanical Engineering, Indian Institute of Technology Bombay, Department of Mechanical Engineering & Materials Science, Duke University

  • Jennifer L Niedziela

    Oak Ridge National Laboratory

  • Xing He

    Department of Mechanical Engineering and Materials Science, Duke University, Mechanical Engineering and Materials Science, Duke University

  • Tyson Lanigan-Atkins

    Mechanical Engineering and Materials Science, Duke University

  • Ayman Said

    Argonne National Laboratory, Argonne Natl Lab, Advanced Photon Source, Argonne National Laboratory

  • Ahmet Alatas

    Argonne National Laboratory, Argonne Natl Lab, Advanced Photon Source, Argonne National Laboratory

  • Douglas L Abernathy

    Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge National Laboratory, Neutron Scattering Division, Oak Ridge National Laboratory, Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6475, USA

  • Yang Ren

    Argonne National Laboratory, Advanced Photon Source, Argonne National Laboratory

  • Bin Gao

    Rutgers Center for Emergent Materials and Department of Physics & Astronomy, Rutgers University, Rutgers University, Rutgers Center for Emergent Materials and Department of Physics and Astronomy, Rutgers University

  • Sang-Wook Cheong

    Rutgers University, Department of Physics and Astronomy, Rutgers University, Rutgers University, New Brunswick, Rutgers Center for Emergent Materials and Department of Physics & Astronomy, Rutgers University, Center for Quantum Materials Synthesis and Department of Physics and Astronomy, Rutgers, the State University of New Jersey, Department of Physics, Rutgers University, Rutgers Center for Emergent Materials and Department of Physics and Astronomy, Rutgers University, Piscataway, NJ, Department of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854, USA, Physics, Rutgers University, Physics and Astronomy, Rutgers University, New Brunswick, Department of Physics and Astronomy, Rutgers University, New Jersey, Rutgers University, Physics and Astronomy, and Laboratory for Pohang Emergent Materials and Max Plank POSTECH Center for Complex Phase Materials, Pohang University of Science, RCEM, Department of Physics and Astronomy, Rutgers U., Rutgers Center for Emergent Materials and Department of Physics and Astronomy, Rutgers University, Department of Physics and Astronomy, 136 Frelinghuysen Road, Piscataway, New Jersey 08854, USA, Rutgers Center for Emergent Materials

  • Olivier Delaire

    Mechanical Engineering and Materials Science, Duke University