Europium (II) oxide
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| __ Eu 2+ __ O 2− | |||||||||||||
| General | |||||||||||||
| Surname | Europium (II) oxide | ||||||||||||
| other names |
Europium monoxide |
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| Ratio formula | EuO | ||||||||||||
| Brief description |
purple solid |
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| properties | |||||||||||||
| Molar mass | 167.96 g mol −1 | ||||||||||||
| Physical state |
firmly |
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| As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . | |||||||||||||
Europium (II) oxide is a chemical compound and is one of the oxides of europium . In addition to europium (II) oxide, europium (III) oxide and the mixed-valence europium (II, III) oxide are also known.
Extraction and presentation
Europium (II) oxide can be produced by reducing europium (III) oxide with elemental europium at 800 ° C and subsequent distillation in vacuo at 1150 ° C.
It is also possible to manufacture it by reacting europium oxychloride with lithium hydride .
In modern research, ultra-thin films of europium oxide are often produced directly from Eu atoms and O 2 molecules using molecular beam epitaxy (MBE) . These films have contamination, including Eu 3+ , of less than 1%.
properties
Europium (II) oxide is a purple solid as a volume crystal and blue-transparent as an ultra-thin film. It is very sensitive to moist air, in which it slowly turns into yellow europium (II) hydroxide hydrate and finally into white europium (III) hydroxide . It also forms carbides (EuC x ) and native oxides (EuO 1 + x , europium (III) oxide , europium (II, III) oxide ). EuO crystallizes in a cubic sodium chloride structure with the lattice parameter a = 0.5144 nm. The stoichiometry of the compound is often not exact, it can contain up to 4% Eu 3+ and also small amounts of elemental europium. In ultra-high vacuum conditions and special oxide MBE systems, however, it has been possible since 2008 to reactively produce high-purity single-crystalline EuO films (see extraction and illustration). These crystal films show properties of a bulk crystal from about 4 nm.
Europium (II) oxide is ferromagnetic, with a Curie temperature of 69.3 K . Enrichment with further elemental europium to about 5–7% increases this to 79 K. This also has a CMR effect , whereby the conductivity of the material rises sharply below the Curie temperature. Another possibility to increase the Curie temperature is doping with gadolinium , holmium or lanthanum .
Furthermore, europium (II) oxide is a semiconductor with a band gap of 1.12 eV .
use
Due to the properties of europium (II) oxide, thin layers of the material that are applied to silicon are examined to act as spin filters . These are materials that only allow electrons with a certain spin to pass, while electrons with a different spin cannot pass. These are of interest for novel electronic components.
Individual evidence
- ^ Ian McGill: Rear Earth Elements. In: Ullmann's Encyclopedia of Industrial Chemistry . Wiley-VCH, Weinheim 2012, doi : 10.1002 / 14356007.a22_607 .
- ↑ This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.
- ↑ a b M. W. Shafer: Preparation and Crystal Chemistry of Divalent Europium Compounds. In: Journal of Applied Physics. 36, 1965, pp. 1145-1152, doi : 10.1063 / 1.1714142 .
- ↑ a b Georg Brauer (Ed.): Handbook of Preparative Inorganic Chemistry . 3., reworked. Edition. tape II . Enke, Stuttgart 1978, ISBN 3-432-87813-3 , p. 1092 .
- ↑ R. Sutarto, et al .: Epitaxial and layer-by-layer growth of EuO thin films on yttria-stabilized cubic zirconia (001) using MBE distillation. In: Phys. Rev. B 79, 2009, pp. 705318-705327, doi : 10.1103 / PhysRevB.79.205318 .
- ^ SG Altendorf, et al .: Oxygen off-stoichiometry and phase separation in EuO thin films. In: Phys. Rev. B 84, 2011, p. 155442, doi : 10.1103 / PhysRevB.84.155442 .
- ↑ a b c Tiffany D. Santos: Europium Oxide as a Perfect Electron Spin Filter . Dissertation, Massachusetts Institute of Technology , 2007.
- ^ C. Caspers, M. Mueller, AX Gray, AM Kaiser, A. Gloskovskii, CS Fadley, W. Drube, CM Schneider: Electronic structure of EuO spin filter tunnel contacts directly on silicon. In: physica status solidi (RRL) - Rapid Research Letters. 5, 2011, pp. 441-443, doi : 10.1002 / pssr.201105403 .
- ↑ German Electron Synchrotron : Perfect Layer for the Right Spin . December 9, 2011.