Europium(II) oxide (EuO) is a chemical compound which is one of the

oxide An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...

s of

europium Europium is a chemical element with the symbol Eu and atomic number 63. Europium is the most reactive lanthanide by far, having to be stored under an inert fluid to protect it from atmospheric oxygen or moisture. Europium is also the softest lanth ...

. In addition to europium(II) oxide, there is also

europium(III) oxide Europium(III) oxide (Eu2O3), is a chemical compound of europium and oxygen. It is widely used as a red or blue phosphor in television sets and fluorescent lamps, and as an activator for yttrium-based phosphors. It is also an agent for the manufact ...

and the mixed valence europium(II,III) oxide.

Preparation

Europium(II) oxide can be prepared by the reduction of europium(III) oxide with elemental europium at 800 °C and subsequent

vacuum distillation Vacuum distillation is distillation performed under reduced pressure, which allows the purification of compounds not readily distilled at ambient pressures or simply to save time or energy. This technique separates compounds based on differences i ...

at 1150 °C. :Eu₂O₃ + Eu → 3 EuO It is also possible to synthesize from the reaction of europium oxychloride and

lithium hydride Lithium hydride is an inorganic compound with the formula Li H. This alkali metal hydride is a colorless solid, although commercial samples are grey. Characteristic of a salt-like (ionic) hydride, it has a high melting point, and it is not solub ...

. :2 EuOCl + 2 LiH → 2 EuO + 2 LiCl + H₂ In modern research, thin films can be manufactured by

molecular beam epitaxy Molecular-beam epitaxy (MBE) is an epitaxy method for thin-film deposition of single crystals. MBE is widely used in the manufacture of semiconductor devices, including transistors, and it is considered one of the fundamental tools for the devel ...

directly from europium atoms and oxygen molecules. These films have contamination of Eu³⁺ of less than 1%.

Properties

Europium(II) oxide is a violet compound as a bulk crystal and transparent blue in thin film form. It is unstable in humid atmosphere, slowly turning into the yellow

europium(II) hydroxide Europium(II) hydroxide is an inorganic compound, with the chemical formula of Eu(OH)2. It can exist as the dihydrate Eu(OH)2·H2O. Preparation The monohydrate of europium(II) hydroxide can be obtained by the reaction of metal europium and 10 m ...

hydrrate and then to white

europium(III) hydroxide Europium(III) hydroxide is an inorganic compound with a chemical formula Eu(OH)3. Chemical properties Europium(III) hydroxide can be prepared by reacting metallic europium with water. It reacts with acids In computer science, ACID ( atomicity, ...

. EuO crystallizes in a cubic

sodium chloride Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...

structure with a lattice parameter a = 0.5144nm. The compound is often

non-stoichiometric In chemistry, non-stoichiometric compounds are chemical compounds, almost always solid inorganic compounds, having elemental composition whose proportions cannot be represented by a ratio of small natural numbers (i.e. an empirical formula); mos ...

, containing up to 4% Eu³⁺ and small amounts of elemental europium. However, since 2008 high purity crystalline EuO films can be created in ultra high vacuum conditions. These films have a crystallite size of about 4 nm. Europium(II) oxide is

ferromagnetic Ferromagnetism is a property of certain materials (such as iron) which results in a large observed magnetic permeability, and in many cases a large magnetic coercivity allowing the material to form a permanent magnet. Ferromagnetic materials ...

with a

Curie Temperature In physics and materials science, the Curie temperature (''T''C), or Curie point, is the temperature above which certain materials lose their permanent magnetic properties, which can (in most cases) be replaced by induced magnetism. The Cur ...

of 69.3 K. With the addition of about 5-7% elemental europium, this increases to 79 K. It also displays

colossal magnetoresistance Colossal magnetoresistance (CMR) is a property of some materials, mostly manganese-based perovskite oxides, that enables them to dramatically change their electrical resistance in the presence of a magnetic field. The magnetoresistance of conventio ...

, with a dramatic increase in conductivity below the Curie temperature. One more way to increase the Curie temperature is doping with

gadolinium Gadolinium is a chemical element with the symbol Gd and atomic number 64. Gadolinium is a silvery-white metal when oxidation is removed. It is only slightly malleable and is a ductile rare-earth element. Gadolinium reacts with atmospheric oxygen ...

holmium Holmium is a chemical element with the symbol Ho and atomic number 67. It is a rare-earth element and the eleventh member of the lanthanide series. It is a relatively soft, silvery, fairly corrosion-resistant and malleable metal. Like a lot of othe ...

, or

lanthanum Lanthanum is a chemical element with the symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements between lantha ...

. Europium(II) oxide is a

semiconductor A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...

with a

band gap In solid-state physics, a band gap, also called an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference (in ...

of 1.12 eV.

Applications

Because of the properties of europium(II) oxide, thin layers of the oxide deposited on

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...

are being studied for use as spin filters. Spin filter materials only allow

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no kn ...

s of a certain

spin Spin or spinning most often refers to: * Spinning (textiles), the creation of yarn or thread by twisting fibers together, traditionally by hand spinning * Spin, the rotation of an object around a central axis * Spin (propaganda), an intentionally b ...

to pass, blocking electrons of the opposite spin.

References

{{oxides Europium(II) compounds Oxides Rock salt crystal structure