Optical properties, lattice dynamics, and structural phase transition in hexagonal 2H-BaMn O3 single crystals

T. N. Stanislavchuk, A. P. Litvinchuk, Rongwei Hu, Young Hun Jeon, Sung Dae Ji, S. W. Cheong, A. A. Sirenko

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Optical properties and lattice dynamics of hexagonal 2H-BaMnO3 single crystals are studied experimentally in a wide temperature range by means of rotating analyzer ellipsometry and Raman scattering. The magnitude of the direct electronic band gap is found to be Eg=3.2eV. At room temperature the far-infrared (IR) ellipsometry spectra reveal six IR-active phonons; two of them are polarized along the c axis and four are polarized within the a-b plane. Seven phonon modes are identified in the Raman scattering experiments. Group theoretical mode analysis and complementary density functional theory lattice dynamics calculations are consistent with the 2H-BaMnO3 structure belonging to the polar P63mc space group at room temperature. All observed vibrational modes are assigned to specific eigenmodes of the lattice. The neutron diffraction measurements reveal a structural phase transition upon cooling below TC=130±5K, which is accompanied by a lattice symmetry change from P63mc to P63cm. Simultaneously, at temperatures below TC several additional IR- and Raman-active modes are detected in experimental spectra. This confirms the occurrence of a structural transition, which is possibly associated with the appearance of electrical polarization along the c axis and a previously known tripling of the primitive cell volume at low temperatures.

Original languageEnglish (US)
Article number134308
JournalPhysical Review B - Condensed Matter and Materials Physics
Issue number13
StatePublished - Oct 29 2015

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics


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