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Wichtige Termine im Wintersemester 2017/2018
  • Beginn der Vorlesungszeit: 09.10.2017
  • Ende der Vorlesungszeit: 02.02.2018
  • Die Vorlesungen fallen aus: 23.12.2017 - 07.01.2018
  • Dies acdemicus: 06.12.2017
  • Feiertage: 31.10.2017, 01.11.2017
BIGS Chemistry

GDCh Ortsverband Bonn

 

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Vorsitzender: Prof. Dr. A. Lützen
Jungchemikerforum Bonn


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KOPO 2017

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Sie sind hier: Startseite Veranstaltungen Dr. Elise Pachoud (University of Edinburgh): Orbital molecules in mixed valent transition metal oxides

Termin: 26.10.2017 Uhrzeit: 17:15 - 19:00 ( Donnerstag )

Dr. Elise Pachoud (University of Edinburgh): Orbital molecules in mixed valent transition metal oxides

AC Kolloquium
Referent/in: Dr. Elise Pachoud
Inhalt:

The electronic properties of transition metal oxides usually result from a coupling between the three degrees of freedom: charge, orbital and spin states. When metal-metal distances are short, direct bonding interactions between M ions having localized t2g orbital order can give rise to more complex quantum electronic states called ‘orbital molecules’. They appear as local structural distortions coupled through cation orbital ordering and sharing of electron density, and are encountered in some mixed-valent transition metal oxides.
In magnetite Fe3O4, distortions of linear Fe-Fe-Fe units into three-site orbital molecules (called trimerons) appears below the Verwey transition, TV=125K. This complex charge ordering distorts the RT cubic spinel Fd-3m structure into a monoclinic Cc supercell. The ground state of Fe3O4 has been shown to be very sensitive to chemical perturbation, changing both the order of the transition and its temperature. We have studied the modifications in the low temperature Verwey phase of non-stoichiometric Fe3(1-δ)O4 and substi-tuted Fe3-xZnxO4 magnetite samples as well as a natural sample by synchrotron X-ray diffraction on micro-crystals.
Low valent vanadium oxides with short V-V distances are also notable for forming large orbital molecules, triangular V39+ clusters in BaV10O15 below 130 K and heptamer V717+ in AlV2O4 below 700 K. The vanadium oxyphosphate V2OPO4  is a good candidate to display such a phenomenon, having short V-V distances and strong orbital overlap within its face-sharing V2.5+O6 octahedra chains. Through powder diffraction studies, we have identified a charge order I41/amd – C2/c transition at 605K, with the tetragonal high temperature phase displaying negative thermal expansion.
 

Öffentliche Veranstaltung: Ja
Ort: Chemische Institute
Adresse: Gerhard-Domagk-Str. 1
Raum: 1.033
Veranstalter: Institut für Anorganische Chemie
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