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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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Eu—Ir system.—Bozo rth et sA. [238] have prepared Eulr2 by sintering the components between 800 and 1050° C. Eulr2 possesses cubic laves phase C15 and does not show [239] any EPB signal. It is believed that the europium in Eulr2 is in the trivalent state. Gdlr2 was found to be isomor-phous with Eulr2.
Eu—N system. — EuN was prepared [240] by direct combination of europium metal and nitrogen at 800° C. Klemm and Winkelmann’s preparation [241] involved heating (7005) a mixture of finely divided europium and KC1 (1:3) in a stream of NH3. EuN, like SmN and YbN possesses the NaCl type structure. The lattice constant of EuN is a = 5.014 A according to Klemm and Winkelmann [241], and a = 5.0U7 ± 0.004 A according to Eick et al [240]. However, the preparation of Eick et al. contained some impurity, possibly as oxide.
Evr—O system- — A detailed discussion on various oxides of europium and the mixed oxides is presented in the next chapter (p. 57).
Eu—S system. — Europium sulphide, EuS, was first prepared by Beck and Nowacki [242] who reported the lattice constant as a = 5.957 ±
Binary Systems 45
0 002 A (isotypic with NaCl). Keemm and Senff [243] li ave reinvestigated the compound along with the selenide and telhiride. They report the lattice constant to be a = 5.956 ± 0.001 A. It has not been possible to prepare any EU2S3. However, Picon et al. [244] have reported the exist-ance of E113S4 which is believed to be a n- ixture of divalent and trivalent europium (Eu2t Eu|hS4). The literature data on the magnetic susceptibilities of EuS and EU3S4 are given below. The Curie temperature [245] for EuS is ~18° K. The lattice constant of EU3S4 was found [244] to be a = 8.537 A.
Xmol * 10fc
Picon et al. [244] Klemm and Senff [243]
EuS EusS4 22600 11500* 20° —78° 23800 35400 -183° 81000
* value for X mol/3
Eu—Sb system. — The physical properties and preparation [227] are described on p. 43.
Eu-St system. — Keemm and Senff [243] first prepared EuSe (brownish black). The magnetic susceptih-iity data and lattice constant are as follows.
^mol ' 10®
a (A) 0 O 1 -a 00 0 -183°
EuS^ 6.173 ± 0.001 24800 39000 85500
I ke EuS, europium selenide becomes [245] ferromagnetic at low temperature (4.2° K). The Curie temperature [245] of EuSe is ~7° K. The saturation moment of EuSe extrapolated to 0° K is 6.7 fiB per Eu2+ ion in good agreement with the theoretical value of 7 j.iB.
Eu—Si system.—EuSi2 b as been prepared by Gkenthal [246] and found to be tetragonal like LaSi2. It has a melting point of 1500° C and a density of 5.5 (g/cm2). Preliminary investigations of Eu—Si alloys containing between 9 and 91 per cent weight of Eu showed the possible existence of at least three silicides [247]. Alloys containing between 9 and 63 per cent weight of Eu consisted of Si and EuSi2.
Eu—Sm system. — Lowering of the melting point of samarium from 1072° to 1052° C has been observed [248] by adding 0.2% of Eu.However, the a ^ p transition temperature of samarium remained unchanged.
46
Alloys and Intermetallic Compounds of Europium
Eu—Te system. — Klemm and Senff [249], and Brixner [227] have investigated EuTe. EuTe like the corresponding sulphide and selenide, has the NaCl type of structure with lattice constant a — 6.572 ± 0.001 A. Unlike the sulphide and selenide, EuTe becomes paramagnetic (or possibly antiferromagnetic) [245, 249] at 4.2° K. Busch et al. [250] were able to induce ferromagnetic spin rearrangements in EuTe by applying a magnetic field upto 120 kOe.
Eu—U system. — Haefling and Daane [251] have studied the limits of solubility of the rare earths, in uranium and uranium in various rare earths, in the temperature range 1000°—1250° C. About 1.12 wt. per cent of uranium is soluble in europium at 1200° C whereas the solubility of europium in uranium at that temperature is only 0.21 wt. per cent.
Ternary Systems
Eu—Gd—8 system. — Unfortunately not many ternary systems containing europium have been investigated. Hulliger and Vogt [252] have prepared the non-metallic TI13P4 (body centered cubic) type EuGd2S4. The ferromagnetic EuGd2S4 has a Curie temperature of 6° K. These authors have also considered the possibility of filling up the cation holes of the TI13P4 structure with various cations of different charge.
EuGd2Se4 and EuGd2Te4 are found to crystallize in the same structure as EuGd2S4.
Chapter 5
Compounds of Europium
During the last few years enormous advances have been made in our understanding of the nature and characteristics of inorganic complexes. Although the d-type transition elements have received the greater part of the chemists1 attention, an increasing interest in the coordination chemistry of the rare earths is noticable. The important role played by complexing agents in the modem separation techniques applied to the rare earths is well recognized. In an earlier review, however, Moeller [253] pointed out that the inner 4/-electrons of tripositive rare earth ions are wellshielded from external influences and the formation of strong covalent bonds is not very favourable. Nevertheless, the absorption spectra of the tripositive rare earth ions do show certain perturbations of these 4/ levels due to complexation. It is considered that this perturbation is caused mainly by a decrease of term differences (see next chapter). However, it is perfectly legitimate to believe that the bonding in rare earth complexes may involve higher energy orbitals, e.g., 6d, 6s, 6p.
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