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Title: Evidence of Eu{sup 2+} 4f electrons in the valence band spectra of EuTiO{sub 3} and EuZrO{sub 3}

Abstract

We report on optical band gap and valence electronic structure of two Eu{sup 2+}-based perovskites, EuTiO{sub 3} and EuZrO{sub 3} as revealed by diffuse optical scattering, electron energy loss spectroscopy, and valence-band x-ray photoelectron spectroscopy. The data show good agreement with the first-principles studies in which the top of the valence band structure is formed by the narrow Eu 4f{sup 7} electron band. The O 2p band shows the features similar to those of the Ba(Sr)TiO{sub 3} perovskites except that it is shifted to higher binding energies. Appearance of the Eu{sup 2+} 4f{sup 7} band is a reason for narrowing of the optical band gap in the title compounds as compared to their Sr-based analogues.

Authors:
 [1];  [2];  [3]; ;  [4];  [5];  [6]
  1. National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan)
  2. Materials Research Laboratory, University of Nova Gorica, Vipavska 13, 5000 Nova Gorica (Slovenia)
  3. International Center for Young Scientists (ICYS), MANA, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan)
  4. Department of Materials Science and Engineering, McMaster University, Hamilton, Ontario L8S 4L7 (Canada)
  5. International Center for Materials Nanoarchitectonics, MANA, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan)
  6. National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan)
Publication Date:
OSTI Identifier:
22089496
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 112; Journal Issue: 8; Other Information: (c) 2012 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; BINDING ENERGY; ELECTRONIC STRUCTURE; ENERGY-LOSS SPECTROSCOPY; EUROPIUM COMPOUNDS; LIGHT SCATTERING; PEROVSKITES; SPECTRA; TITANATES; TITANIUM OXIDES; X-RAY PHOTOELECTRON SPECTROSCOPY; ZIRCONATES

Citation Formats

Kolodiazhnyi, T., Valant, M., Williams, J. R., Bugnet, M., Botton, G. A., Ohashi, N., and Sakka, Y.. Evidence of Eu{sup 2+} 4f electrons in the valence band spectra of EuTiO{sub 3} and EuZrO{sub 3}. United States: N. p., 2012. Web. doi:10.1063/1.4761933.
Kolodiazhnyi, T., Valant, M., Williams, J. R., Bugnet, M., Botton, G. A., Ohashi, N., & Sakka, Y.. Evidence of Eu{sup 2+} 4f electrons in the valence band spectra of EuTiO{sub 3} and EuZrO{sub 3}. United States. doi:10.1063/1.4761933.
Kolodiazhnyi, T., Valant, M., Williams, J. R., Bugnet, M., Botton, G. A., Ohashi, N., and Sakka, Y.. Mon . "Evidence of Eu{sup 2+} 4f electrons in the valence band spectra of EuTiO{sub 3} and EuZrO{sub 3}". United States. doi:10.1063/1.4761933.
@article{osti_22089496,
title = {Evidence of Eu{sup 2+} 4f electrons in the valence band spectra of EuTiO{sub 3} and EuZrO{sub 3}},
author = {Kolodiazhnyi, T. and Valant, M. and Williams, J. R. and Bugnet, M. and Botton, G. A. and Ohashi, N. and Sakka, Y.},
abstractNote = {We report on optical band gap and valence electronic structure of two Eu{sup 2+}-based perovskites, EuTiO{sub 3} and EuZrO{sub 3} as revealed by diffuse optical scattering, electron energy loss spectroscopy, and valence-band x-ray photoelectron spectroscopy. The data show good agreement with the first-principles studies in which the top of the valence band structure is formed by the narrow Eu 4f{sup 7} electron band. The O 2p band shows the features similar to those of the Ba(Sr)TiO{sub 3} perovskites except that it is shifted to higher binding energies. Appearance of the Eu{sup 2+} 4f{sup 7} band is a reason for narrowing of the optical band gap in the title compounds as compared to their Sr-based analogues.},
doi = {10.1063/1.4761933},
journal = {Journal of Applied Physics},
number = 8,
volume = 112,
place = {United States},
year = {Mon Oct 15 00:00:00 EDT 2012},
month = {Mon Oct 15 00:00:00 EDT 2012}
}
  • The He I photoelectron spectra of ({eta}{sup 5}-C{sub 5}H{sub 4}CH{sub 3})Mn(CO){sub 2}HSiHPh{sub 2}, ({eta}{sup 5}-C{sub 5}H{sub 4}CH{sub 3})Mn(CO){sub 2}HSiPh{sub 3}, and ({eta}{sup 5}-C{sub 5}H{sub 4}CH{sub 3})Mn(CO){sub 2}HSiFPh{sub 2} (Ph = C{sub 6}H{sub 5}) have been obtained in order to measure the nature and extent of Si-H bond interaction with the transition-metal center in these complexes. The principal electronic structure factors contributing to the addition of the Si-H bond to the transition metal involve the interaction of the Si-H {sigma} and {sigma}* orbitals with the metal. The extent of Si-H {sigma}I interaction with the metal is obtained from the shape andmore » splitting pattern of the metal-based ionization band. The electron distribution between the Si-H bond and the metal is indicated by the relative stabilities of the metal-based and ligand-based ionizations. It is found that the metal-based ionizations of these complexes reflect the formal d{sup 6} electron count at the metal center. Also, the small shifts of the valence ionizations reveal that the extent of electron charge density shift from the metal to the ligand is negligible. These observations show that the electronic structure of the Si-H interaction with the metal is in the initial stages of Si-H bond addition to the metal, before oxidative addition has become prevalent.« less
  • Raman-scattering spectra of (Eu{sub 2/3}Ce{sub 1/3}){sub 2}(Ba{sub 2/3}Eu{sub 1/3}){sub 2}Cu{sub 3}O{sub 9} and (Er{sub 2/3}Ce{sub 1/3}){sub 2}(Ba{sub 2/3}La{sub 1/3}){sub 2}Cu{sub 3}O{sub 9}, both of which have Cu-O{sub 5} pyramid structure, as well as YBa{sub 2}Cu{sub 3}O{sub 7}, have been observed at room temperature with use of single crystals. A scattering peak with {ital B}{sub 1{ital g}} symmetry has been observed at around 180 cm{sup {minus}1} and peaks with {ital A}{sub 1{ital g}} symmetry at around 220, 290, 450, and 540 cm{sup {minus}1}, in both compounds. The 180-cm{sup {minus}1} peak with {ital B}{sub 1{ital g}} symmetry is assigned to the out-of-phasemore » bending of oxygen in the Cu-O{sub 2} plane and the 540-cm{sup {minus}1} peak with {ital A}{sub 1{ital g}} symmetry to the stretching of apical oxygen. Phonon-energy calculation has been performed with use of ionic potentials obtained for YBa{sub 2}Cu{sub 3}O{sub 7}. To explain the observed {ital B}{sub 1{ital g}} phonon energies, it has been found that the polarizability of the oxygen in the Cu-O{sub 2} plane in these compounds must be increased in relation to that in YBa{sub 2}Cu{sub 3}O{sub 7}. The 220- and 290-cm{sup {minus}1} peaks are tentatively assigned to the mixed vibrational modes of oxygens in the Cu-O{sub 2} plane and lanthanide atoms.« less
  • The existence of an antiferrodistortion transition in EuTiO{sub 3} is disputable, and this question needs to be answered. One of the possible causes is the presence of an Eu{sup 3+} impurity in a sample. A nonempirical polarizable ion model is used to study the effect of a trivalent Eu{sup 3+} ion impurity on the antiferrodistortion and ferroelectric instabilities of an EuTiO{sub 3} crystal in the bulk and the thin-film states. Lattice dynamics calculation shows that a bulk impurity-free EuTiO{sub 3} crystal has no unstable modes throughout the entire phase space volume. The addition of an Eu{sup 3+} impurity leads tomore » a significant softening of the rotational mode, the distortion in which makes tetragonal phase I4/mcm (which is experimentally observed) energetically favorable. In going from the bulk crystal to the thin film, the vibration spectrum of the impurity-free film has unstable antiferrodistortion and rotational modes. The addition of an Eu{sup 3+} impurity enhances the antiferrodistortion instability, which fully or partly suppresses ferroelectricity.« less
  • The valence photoelectron spectra of ({eta}{sup 5}-C{sub 5}H{sub 4}CH{sub 3})Mn(CO)(L)HSiCl{sub 3} and ({eta}{sup 5}-C{sub 5}H{sub 4}CH{sub 3})Mn(CO)(L)HSiHPh{sub 2}, where L is CO or P(CH{sub 3}){sub 3}, are compared to determine the effect of ligand substitution at the metal center on Si-H bond activation. Metal centers that are more electron rich may promote more complete oxidative addition of the Si-H bond to the metal. The shifts in the metal and ligand ionization energies and the relative intensities of ionizations in the He I and He II photoelectron experiments show that the metal in ({eta}{sup 5}-C{sub 5}H{sub 4}CH{sub 3})Mn(CO)(PMe{sub 3})HSiCl{sub 3} ismore » best represented by a formal oxidation state of III (d{sub 4} electron count). This indicates nearly complete oxidative addition of the Si-H bond to the metal center and results in independent Mn-H and Mn-Si bonds. In contrast, the splitting and intensity pattern of the metal-based ionizations of ({eta}{sup 5}-C{sub 5}H{sub 4}CH{sub 3})Mn(CO)(PMe{sub 3})HSiHPh{sub 2} reflect the formal d{sup 6} electron count of a metal corresponding to oxidation state I. The extent of electron charge density shift from the metal to the ligand is also small, as evidenced by the negligible shifts of these ionizations from those of the related ({eta}{sup 5}-C{sub 5}H{sub 4}CH{sub 3})Mn(CO){sub 2}(PMe{sub 3}) complex. These observations indicate that the electronic structure of the Si-H interaction with the metal in this complex is in the initial stages of Si-H bond addition to the metal, before oxidative addition has become prevalent. 25 refs., 6 figs., 1 tab.« less
  • Polarized emission and absorption spectroscopy of 4f{sup 6} Eu{sup 3+} in Na{sub 3}[Yb{sub 0.95}Eu{sub 0.05}(dpa){sub 3}]{center_dot}NaClO{sub 4}{center_dot}10H{sub 2}O (dpa = dipicolinate) is reported with the objective of characterizing the crystal-field energy levels. Empirical and theoretical studies were compared by fitting a parameterized Hamiltonian to the data.