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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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Fig. 13 a
Eu203
11
Composition, mole %
AI2O3
31 2n 3-S
Fig. 13b EU2O3 Composition, mole % Ga2O3
62
Compounds of Europium
V
Fig. 13 c
EU2O3
1:1
Composition, mote %
Cr20 3
Fig. 13 e
Fig. 13d
Eu203
/•*/ 3'5 Composition, mo/e %
Fe203
EU2O3
1:7
Composition, mote %
Sc203
Fig. 13 a-e. Phase diagrams of Eu2Os and A2Os systems a) A — AI, b) A
Ga, c) A = Cr, d) A = Fe, e) A = Sc
- -.....r ItlfAlf* ■ r“:~n-y-' -\ - '\- -1 \ nftlfcM •
Inorganic Coordination Compounds
63
7:7
EU2O3 Composition, mole % In203
Fig. 14. Phase diagram of Eu203—In2Os
the sample changed only slightly during reduction. This suggests that anion vacancies and electrons have a low mobility. The reduced form of europium oxide absorbs oxygen at all temperature down to — 78° C. Curtis and Tharp [305] report the following properties of EU2O3: molar sp. heat 33.31 cal/mol/° C, thermal expansion 10.3 X 10~8 in/° C. The B—C inversion temperature is 1050° C. At this temperature the inversion rate is slow whereas at 1400° C the inversion is completed within 2 hrs. or less.
EuO. — This lower oxide of europium was prepared by the reduction of EU2O3 with lanthanum metal at 1300 — 1500° C by Eick et al. [319]. EuO has a NaCl type structure with a — 5.1439 ± 0.0005 A. Garton and Hukin [320] attempted the preparation of EuO by controlled oxidation of europium metal at 350° C with a stoichiometric addition of oxygen and obtained the oxide in fairly pure state. They also tried the thermal decomposition of EuCOs, Eu(HCOO)2 and Eu(OH)2. Only Eu(OH)2 proved to be advantegeous and gave a sample of EuO of reasonable purity.
EuO is found [321] to be truly ferromagnetic at 77° K with a saturation moment of ~7 Bohr magnetons. Nereson, Olsen and Arnold
[322] have confirmed this behaviour of EuO by neutron diffraction studies.
64
Compounds of Europium
Fig. 15 a
u
0
1 u
§ 7650 -
I
^SS+^ss
I
lss
BSS
J_L
0 20 w 60 80 100 La203 Composition, mole% Euz03
Fig. 15b
NCI2O3
Composition, moie°/o
EU2O3
Bss
0 20 W 60 80 100 Fig. 15c Sm203 Composition, mo/e % Euz03
Fig. 15 a-c. Phase diagrams of Eu2Os with a) La203 b) Nd2Os and c) Sm203
EuaOi. — Another lower oxide of europium, E113O4, having a dark red colour, was first obtained by Archabd [47] during the heating of EU2O3 with varying amounts of graphite in a Solar furnace. Babnighausen and Bbatjeb [323] reinvestigated this oxide and gave a method of preparation. According to these investigators EU3O4 can be prepared by heating an equimolar mixture of EuO and EU2O3 in an inert atmosphere at 900° C for two hours. The rhombic EU3O4 belongs [323] to the same
I
§ 1650
1
Inorganic Coordination Compounds
65
1650
B
ss
J_I_I_I_I_I_L
Eu203
1650 - BSS
GCI2O3
TLJ ©
r\
I
■fe Eu2Q3
& t*
BSS+CSS I Css -I I
J_ __l_I_I_I_L
1650 - BSS
Bss+Css
'SS
J_I_I_I I
EU2O3
7650
3SS
! !
[Bss^Cssj
! 1
Css
J_I_1_I_I_I_L
0 20 VO 60 80 100
EU2O3 Et203
1650
BSS
Bss
Css
Dy203 EU2O3
1650
Bss
Bss
+
Css
'SS
t I I_I_I_I I I I
Tm203
#ss
1 I_I_I_I_I_I_1_L
Ho203 Eu203
Vb203
1650
Bss
Bss
+
Css
Css
J_I_I_I_I_I_I_I_L
0 20 W 60 80 100 EU2O3 LU2O3
Composition, mole %
Fig. 16. Phase diagrams of Eu203 with Gd2Os, Dy203, Ho203, Er203, Tm20

Yb2Oa and Lu,0
2W3
space group as Eu2SrC>4 (Pnam) with lattice constants a = 10.094 ± ± 0.003, b = 12.068 ± 0.003 and c = 3.500 ± 0.001 A. A complete structural analysis of EU3O4 by single crystal X-ray diffraction data has been reported recently by Ratj [324]. This compound is found to contain both divalent and trivalent europium ions and is isomorphous with CaFeaCU. The crystal parameters as determined by Rau are as follows, a = 10.085 ± 0.002, b = 12.054 ± 0.002 and c = 3.502 ± 0.001 A, which compare well with those of Babnighattsen and Brauer [323]. The unit cell of E113O4 contains four formula units. There is a sixfold coordination of oxygens around each Eu3+ ion forming a distorted octahedron (Fig. 17). The coordination around the Eu2+ ion is an eightfold one with each Eu2+ ion lying at the center of a triangular prism of six
5 Sinha, Europium
66
Compounds of Europium
oxygen atoms. The other two oxygen atoms lying out from the centers of two of the prism faces complete the coordination.
Fig. 17. Europium coordination polyhedra in Eu304 a) Trivalent Eu (1) polyhedron, b) Trivalent Eu (2) polyhedron, c) Divalent Eu (3) polyhedron
Several authors have obtained a yellowish product during the reduction of EU2O3 in silica tubes. This yellowish product is more likely to be europium silicate (see below) than a new form of oxide.
EuBOs. — Rare earth borates of the type MBO3, where M = Sm—Lu and Y, are isostructural with vaterite ((x—CaCOs). The lattice constants [325] of EuBOs are a = 3.842 and c = 8.937 Â. Lanthanum borate, however, crystallizes in the aragonite structure [306]. Europium borate and the above mentioned borates can be obtained by the reaction of the metal oxide and B2O3 in an equimolar ratio at 1200—1400° C in air.
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