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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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Euc.5Pao.5O2. — The system Pa205 — M2O3 (where M — rare earth or actinide) has been investigated [327]. It has been found that the ternary oxides of the composition Mo.5Pao.5O2 (cubic, fluorite type) show a great solubility for the corresponding M2O3. The following solubilities of the M2O3 oxides in Mo.5Pao.5O2 at 1250° C have been reported. The decrease
M3+ La Nd Sm Eu Ho Tm Lu
Solb. (mole %) 62 49 45 42 33 29 25
in solubility of the rare earth oxides was found to be proportional to the lattice constant of the mixed oxide.
EuzSiOz. —The reaction of EuO and Si02 above 1200° C in a vacuum or under a hydrogen atmosphere results [328] in europium orthosilicate. This lemon yellow silicate is insoluble in water and is resistant towards
Inorganic Coordination Compounds
67
oxidation at room temperature. Eu2Si(>4 has a very unusual crystal structure. The lattice constants [329] of the orthorhombic cell are a = 9.713, b — 49.56 and c = 5.652 A with 28 formula units per cell. The unusually long b axis is of particular interest. There appears to be layering along the b axis, the true b parameter repeating every seven layers. The measured density is 6.74 g/cc. Eu2SiC>4 is found to be ferromagnetic [328] with a Curie temperature (0) of 7° K. This temperature is about the same as for EuSe which has a nearest neighbour Eu distance of ~ 4.4 A. The nearest neighbour Eu distance in Eu2Si04 may be similar (~ 4.4 A) to that in EuSe assuming a sixfold coordination. The magnetic moment for Eu2Si04 powder [328] at 0° K is 170, and that for a single crystal [328] is 184. These values are somewhat lower than the theoretical value of 197 for the formula Eu2SiC>4, which suggests the presence of trivalent europium (J = 0) explained by assuming a solid solution between Eu4(Si04)3 and Eu2SiC>4.
Two other silicates of europium, EuSiC>3 and Eu^SiOs, found in the EuO—SiC>2 system are isostructural with strontium silicate (Sr2Si04). EuzSrO*. — This compound was prepared by Barnighausen and Bratter
[323] by heating an equimolar mixture of SrCC>3 and EU2O3 at 1000° C for six hours in air. The lattice constants are a = 10.133 ± 0.003, b — 12.081 ± 0.003 and c = 3.4979 ± 0.0005 A. Eu2Sr(>4 belongs to the space groups Pnam.
E112O2 ■ 3TazO<a. — The rare earths from La to Er and also Y have been found [330] to form ternary oxides with Ta20s of the type M2O3 • 3 Ta20s having a perovskite structure. The other rare earths (Tm—Lu) form a mixture of MTaC>4 and Ta2Os- EU2O3 • 3 Ta20s has the following lattice constants a — 3.871, b = 3.885 and c = 7.792 A.
LiEuOz.—According to Barnighausen [331,332] LiEuC>2 exists in two polymorphic forms. a-LiEu02 is monoclinic (P 2i/c) with a = 5.6815 ± 0.0005, b = 5.9885 + 0.0005, c = 5.6221 ± 0.0005 A and ft = 103° 10' ± 3'. The a-form is easily obtained [331] by heating an equimolar mixture of Eu20s(C-form) and Li20 with twice the amount of LiCl at 650° in a vacuum. /?-LiEu02 is rhombic [332] with a = 11.405 ± 0.001, b = 5.3353 ± 0.0005 and c = 3.4711 ± 0.0003 A, and can be prepared by heating a mixture of L12O (5% in excess of the theoretical value) and EU2O3 (C-form) for 12 hours at 800° C.
RU2EU2O7. — Rare earth compounds of the pyrochlore type, RU2M2O7, belong to the space group FdSm (Oj) and show analogy with the structures of UO2 and U4O8. The lattice parameter [333] of RU2EU2O7 is a = 10.252 A.
5*
68
Compounds of Europium
Oxysalts
OxyhcUides
Oxyfluoride. — Hydrolysis of EuFs gives the corresponding oxyfluoride
[334]. This hydrolysis of the anhydrous fluoride can be easily effected by heating it at 800° C in a current of moist air. All rare earth oxyfluorides except CeOF, have the rhombohedral structure (LaOF type). The lattice constants for EuOF are: a = 6.827 ± 0.002 A and a = 33.05 ± 0.02°.
Oxychloride. — The rare earth oxychloiides from La to Ho are tetragonal
[335] and isotypic with PbFCl. The oxychlorides of Tm, Yb and Lu have a different structure. PbFCl belongs to the space group D\n (P 4/nmm). The lattice parameters of the rare earth oxychlorides as determined by Templeton and Dauben [335] are tabulated in Table 23. The samples of oxychlorides used by Templeton and Dauben were prepared by the reaction of the oxides with appropriate mixtures of water and HC1 vapour at an elevated temperature.
Table 23. A comparison of the lattice constants of the rare earth oxychlorides
Oxychloride a (A) с :(A) unit cell vol.
LaOCl 4.119 ± 0.002 6.883 ± 0.004 116.78
CeOCl 4.080 ± 0.004 6.831 ± 0.007 113.71
PrOCl 4.051 ± 0.002 6.810 ± 0.006 111.76
NdOCl 4.018 ± 0.002 6.782 ± 0.004 109.49
SmOCl 3.982 ± 0.001 6.721 ± 0.002 106.57
EuOCl 3.965 і 0.004 6.695 і 0.007 105.25
GdOCl 3.950 ± 0.002 6.672 ± 0.004 104.10
TbOCl 3.927 ± 0.004 6.645 ± 0.007 102.47
DyOCl 3.911 ± 0.003 6.620 ± 0.006 101.26
HoOCl 3.893 ± 0.003 6.602 ± 0.004 100.06
ErOCl 3.880 ± 0.02 6.58 ± 0.06 99.1
YbOCl 3.903 ± 0.002 6.597 ± 0.004 100.49
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