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Europium - Sinha S.P.

Sinha S.P. Europium - Springer-Verlag, 1967. - 88 p.
Download (direct link): europium1967.djvu
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2.40
2.20
2.00
1.80
^ 1.60
11M0 'b ї>
1.20 1.00
m
0.80
Fig. 11. Darken-Gurry map for europium (reproduced from The Rare Earths,
John Wiley with the kind permission of the author and the publisher)
It will be seen from the figure that the rare earths fall near the edge of the larger ellipse suggesting that they may exhibit only limited solubility in europium. It is interesting that Mg and Th, which dissolve the other rare earths to an appreciable extent, are apparently excluded.
It is rather unfortunate that only a very limited amount of information on europium alloys and intermetallic compounds is available in the literature. In the following pages an attempt has been made to collect the available data on alloys containing europium.
Binary Systems
Eu—Al system. — E11AI2 has been prepared by the induction melting of a mixture of stoichiometric amounts of the components in an argon
aH
T
~T<
T
Mn+e
•Se °Au
Cr+s°oPRh т p, -Os 4p
Re’Pd As Mo °Po V °TL
NioCoU°Si oA9 0Hg 0Pb
Fe° J^Nb°Ta °sCs Bl Co° °Mn t* oPu«
Cfi °РіҐЯо o°Sn+2
7 Al Cd° °Pu'w-5
Hf°°Zr Се+зе °Be 60 / -
In°
Sc o “
Europium • Extensive solid soly.
■ Umi fed or no solid soly. o No in formation
_L
-Rb Cs Fr -
_JL
o o
0.80 100 1.20 1.40 1.60
1.80 2.00 2.20 2.40 2.60 2.80 Radius,(CN = 12) * a
Binary Systems
43
atmosphere. It possesses the MgCu2 structure [225] with a = 8.125 A. Europium appears to have a valency close to two in this compound. Electron paramagnetic resonance studies at 55 kMc. between 100 and 300° K showed [225] a large temperature dependent Knight shift of Al.
Eu—As system. — Brixner [227] has reported the preparation of arsenides, antimonides and tellurides of the type MA (M = rare earths, Sc, Y and A = As, Sb, Te) and has studied the structural and electrical properties of these compounds. The compounds were prepared by direct synthesis from the elements in an argon atmosphere. All compounds possess a grey metallic appearance and crystallize in the NaCl structure. The following physical properties on EuAs and EuSb are available [227].
Resistivity Seebeck coeff.
(mß cm) (juvr C)
Eu As 1.8 +25
EuSb 35.9 +55
Eu—B system.—EuBe was prepared [228] by reacting EU2O3 with boron. This hexaboride exhibited considerable ranges of homogeneity. It has a cubic structure. The lattice constant varies according to the conditions of preparation.
a — 4.170 A; preparation with a deficiency of boron
a — 4.184 A; preparation containing an excess of boron
The lattice constant of apparently stoichiometric preparations was 4.178 A. Samsonov et al. [229] reported a lattice constant of 4.167 ±
0.002 A.
Hoyt and Chorne [230] have recently reported the preparation of several self-bonded dense borides. EuBe (90%) was made by hot vacuum pressing in graphite dies at ~ 1800—2000° C. Temperature, pressure and time are important variables. Unsuccessful attempts have been made to prepare EuB4.
Eu—C system— The black dicarbide, EuC2, was prepared by Gebelt and Eick [231] by the reaction of europium metal with graphite (1:2 ratio) in a steel bomb at about 1050° C. The compound has a body-centered tetragonal structure with the lattice parameters a = 4.045 and c = 6.645 A. The lattice constants compare reasonably well with SrC2 (a = 4.11, c = 6.68 A).
The temperature dependence of the vapour pressure of europium in equilibrium with solid europium dicarbide and graphite has also been studied recently [232] over a temperature range of 1130 to 1600° K. The
44 Alloys and Intermetallic Compounds of Europium
entropy for the dissociation of EuCs was calculated to be 18.43 ± 1.75 e, u. The Ktandard heat and free energy of formation of EuC2 were found to be —9.17 ± 1.15 kcal and —7.47 ± 1.87 kcal respectively.
A second phase was found to be present i i all preparations. This phase could not be removed but was reduced to a minority by heating at 1060°. The X -ray diffraction pattern did not agree with a M2C3 or M3O phase [233].
Eu—Cd system. — EuCde can be prepared by heating a mixture containing the appropriate stoichiometric amounts of the components [234\. The solubility diagram of europium in liquid uadnrum indicates that the equilibrium solid phase is EuCdn. The powder diagram shows that EuCdn contains a body centered tetragonal cell [234, 235] vith a — 11.93 and c = 7.65 A. It is isostructural with BaCdn, SrCdn, CeZnn, LaZnn and PrZnn.
Eu—D system. — Europium deuteride was found to be isostructural [236] with alkaline earth hydrides and ytteibium deuteride. The sample of the deuteride was prepared by reacting deuterium with the europium and had a maximum composition of EuDi.95. The lattice constants of europium deuteride are a = 6.21, b = 3.77, c = 7.16 A (±0.02 A). The deuterides of europium and ytterbium are believed to be predominantly ionic rather than interstitial.
Eu—H system.—The lighter rare earth trihydrides have a face centered cubic structure whilst those of samarium and the heavier lare earths are hexagonal close packed. Europium and ytterbium, however, form ortho-rhombic dihydrides [236]. Although it has been possible to prepare [237] a hydride of ytterbium with empirical formula YbH2.55 all attempts to prepare the europium trihydride failed.
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