N.C.S.R. "Demokritos"

Research

Department of Materials Science

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Strongly correlated systems (manganites)

Ninety years from the discovery of quantum mechanics a numerous of physical problems, as the energy spectra of atoms, of molecules and simple elemental compounds satisfactorily have been interpreted. Despite the extraordinary progress that has been made, several phenomena exist without an explanation which based on the first principle. These problems mainly related, with transition metal complex oxides where the plausible picture of semiconductor or simple metal is not enough to explain the observed physical properties. The main question that needs to be answered in this category of compounds is, how do the electronic properties these oxides change by changing the number of valence electrons? Classic examples of this category are the high Tc superconductors and manganese perovskites. As a example of our recent research efforts we mention representative experimental results of the compound La1-xCaxMnO3 (0 < x < 1). Using powder neutron and ultra high resolution x-ray diffraction data we realized that the ground state for x > 0.5, of the particular system may concern charge and spin density waves a fact very useful toward to a more deep understanding of the strongly electron correlated systems. For 0.1 < x < 0.23 where the ground state is ferromagnetic insulated we find that the orbital ordering of the eg Mn electrons may be the physical origin of the particular ground state.

Relevant journal articles

  • Pissas, M., Margiolaki, I., Papavassiliou, G., Stamopoulos, D., Argyriou, D. (2005) Crystal and magnetic structure of the La1-xCaxMnO3 compound (0.11 < x < 0.175), Physical Review B 72, 1-15.
  • Pissas, M., Margiolaki, I., Prassides, K., Suard, E. (2005) Crystal and magnetic structural study of the La1-xCaxMnO3 compound (x=34), Physical Review B - Condensed Matter and Materials Physics 72, 1-10.
  • Kallias, G., Pissas, M., Hoser, A. (2000) Neutron diffraction study of La0.5Ca0.5MnO3 under an external magnetic field, Physica B: Condensed Matter 276, 778-779.
  • Simopoulos, A., Pissas, M., Kallias, G., Devlin, E., Moutis, N., Panagiotopoulos, I., Niarchos, D., Christides, C., Sonntag, R. (1999) Study of Fe-doped La1-xCaxMnO3 (x?1/3) using Mo?ssbauer spectroscopy and neutron diffraction, Physical Review B - Condensed Matter and Materials Physics 59, 1263-1271.
  • Department of Materials Science, N.C.S.R. "Demokritos", 153 10 Aghia Paraskevi, Attiki, phone: +30 210 6503381, fax: +30 210 6519430
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