Reports of the Academy of Sciences of the USSR
1963. Volume 153, No. 6

CHEMISTRY

HARI DEV BHARGAVA, L. M. KOVBA, L. I. MARTYNENKO,
Academician Vikt. I. SPITSYN

STUDY OF THE INTERACTION BETWEEN OXIDES OF RARE-EARTH AND ALKALINE-EARTH METALS

As is known, in the series of rare-earth elements from lanthanum to lutetium and from lanthanum to scandium there is a noticeable weakening of the basic properties. This leads to the fact that scandium \((^{1,2})\), and apparently lutetium and ytterbium \((^3)\), exhibit amphoteric properties. Thus, sodium lutetiate and ytterbiate of composition \(\mathrm{Na_3[Lu(OH)_6]}\) and \(\mathrm{Na_3[Yb(OH)_6]}\) \((^3)\) have been described. Recently the compound \(\mathrm{SrEu_2O_4}\) was obtained, which proved to be isostructural with calcium ferrite \(\mathrm{CaFe_2O_4}\) \((^4)\).

It was of interest to establish in what cases amphotericity would be manifested by the oxides of rare-earth elements and what influence the sizes of the ions would have in this process. For this purpose the interaction of strontium oxide with a group of oxides of rare-earth elements, whose ionic radii differ appreciably, was studied: \(\mathrm{La^{3+}}\) (1.06), \(\mathrm{Sm^{3+}}\) (0.96), \(\mathrm{Dy^{3+}}\) (0.91), \(\mathrm{Yb^{3+}}\) (0.85). To check the influence of the size of the alkaline-earth-element ion, the reactions of \(\mathrm{Sm_2O_3}\) with \(\mathrm{BaO}\) and \(\mathrm{CaO}\), and also of \(\mathrm{Yb_2O_3}\) with \(\mathrm{CaO}\), were studied.

Carefully ground oxides of rare-earth elements and oxalates, carbonates, or nitrates of alkaline-earth elements, taken in calculated amounts, were calcined in corundum crucibles in air. In some cases the mixture of oxides was treated with nitric acid and the mixture of nitrates was calcined. The resulting preparations were examined by X-ray phase analysis (RKD-57 camera, Cu \(K_{\alpha}\) radiation, Ni filter).

The results of the X-ray phase analysis are given in Table 1.

Table 1

* The same results were obtained with oxalates and nitrates.
* The oxides of alkaline-earth metals are apparently obtained in the amorphous state or are poorly crystallized; therefore, only the lines of the rare-earth-element oxide are present on the X-ray patterns.
** The same with nitrates.

As is clear from the data of Table 1, calcium oxide does not react with ytterbium and samarium oxides and, apparently, does not dissolve in them. In the case of ytterbium oxide, this is indicated by the constancy of the lattice parameter. For monoclinic samarium oxide the lattice parameters cannot be calculated with sufficient accuracy, but the absence of a noticeable shift of the samarium oxide lines at large \(\theta\) shows that the parameters practically do not change.

Table 2

Results of indexing the X-ray diffraction pattern of SrSm₂O₄

| \multicolumn{5}{c}{SrSm₂O₄} | \multicolumn{2}{c}{CaFe₂O₄ (5)} |
|---|---|---|---|---|---|---|
| I | hkl | d | 1/d² found | 1/d² calc. | I | hkl |
| — | — | — | — | — | 20 | 120
200 |
| — | — | — | — | — | 5 | 220 |
| Med. | 040
320 | 3.001
2.934 | 0.1110
0.1162 | 0.1096
0.1158 | 100 | 040
220 |
| Br. | 121
140 | 2.897 | 0.1192 | 0.1188
0.1194 | 65 | 121
201 |
| Weak | 201 | 2.878 | 0.1207 | 0.1208 | | |
| V. v. weak | 211 | 2.791 | 0.1285 | 0.1277 | | |
| V. weak | 131 | 2.544 | 0.1545 | 0.1530 | 20 | 131 |
| V. v. weak | 311 | 2.378 | 0.1760 | 0.1768 | 25 | 311
420 |
| V. v. weak | 420
150
231 | 2.345 | 0.1820 | 0.1846
0.1811
0.1825 | 25 | 311
420 |
| V. v. weak | 141 | 2.231 | 0.2010 | 0.2010 | 15 | 141 |
| Br. | 241
331 | 2.078 | 0.2316 | 0.2304
0.2316 | 40 | 241
401 |
| Med. br. | 401 | 2.047 | 0.2387 | 0.2388 | 40 | 241
401 |
| V. v. weak | 260 | 1.862 | 0.2883 | 0.2859 | 15
10
20 | 411
051
520
260 |
| V. v. weak | 251 | 1.855 | 0.2906 | 0.2921 | | |
| V. v. weak | 530 | 1.796 | 0.3100 | 0.3072 | | |
| Med. | 002
450 | 1.751 | 0.3262 | 0.3262
0.3284 | | |
| Br. | 360
511 | 1.727 | 0.3355 | 0.3350
0.3340 | 20 | 360 |
| Br. | 161
351 | 1.717 | 0.3393 | 0.3380
0.3412 | | |
| Med. | 441
170 | 1.696 | 0.3479 | 0.3483
0.3455 | 20 | 600
161 |
| Med. br. | 600
521
022 | 1.681 | 0.3339 | 0.3536
0.3545
0.3536 | 25 | 441
002
521 |
| Weak | 202
261 | 1.651 | 0.3671 | 0.3654
0.3674 | 15 | 261 |
| V. weak | 531 | 1.603 | 0.3894 | 0.3887 | 8 | 630
460 |
| V. v. weak | 469
451
361 | 1.565 | 0.4083 | 0.4038
0.4099
0.4142 | | 361 |
| Weak | 042
601
080
541 | 1.516 | 0.4351 | 0.4361
0.4351
0.4384
0.4367 | 20 | 640 |
| Br. | 322
611 | 1.507 | 0.4403 | 0.4420
0.4420 | 10 | 180 |
| Med. | 621
640 | 1.468 | 0.4640 | 0.4626
0.4631 | 25 | 382
042 |
| V. v. weak | 280
152 | 1.446 | 0.4786 | 0.4777
0.5062 | | |
| V. v. weak | 720
152
371 | 1.404 | 0.5073 | 0.5086
0.5072
0.5056 | 10
10 | 720
461
371 |
| V. v. weak | 181 | 1.372 | 0.5316 | 0.5298 | 8 | 422 |
| V. v. weak | 432
641
730 | 1.356 | 0.5440 | 0.5450
0.5447
0.5429 | 2 | 181 |

(continued)

| \multicolumn{5}{c}{SrSm₂O₄} | \multicolumn{2}{c}{CaFe₂O₄ ()} |
|---:|---:|---:|---:|---:|---:|---:|
| I | hkl | d | 1/d² found | 1/d² calc. | I | hkl* |
| Tr. | 281 | 1.337 | 0.5592 | 0.5592 | 2 | 711 |
| Tr. | 471
512
561 | 1.317 | 0.5765 | 0.5744
0.5784
0.5737 | | |
| Tr. | 740
721
442 | 1.301 | 0.5906 | 0.5909
0.5902
0.5930 | 10 | 281
740
561
721 |

Strontium oxide reacts with the oxides of ytterbium, dysprosium, and samarium, forming isotypic compounds Me^II^Me₂^III^O₄, which are isostructural with calcium ferrite and crystallize in the rhombic system. The same compound is formed as a result of the reaction of Sm₂O₃ with BaO. Table 2 gives the results of indexing the Debye pattern of SrSm₂O₄ (the radiographs of SrYb₂O₄, SrDy₂O₄, and BaSm₂O₄ are indexed analogously). Comparison of the line intensities of the X-ray patterns of SrSm₂O₄ and CaFe₂O₄ makes it possible to assign SrSm₂O₄ unambiguously to the structural type of calcium ferrite (space group Pnam). The numerous coincidences of lines with different indices in the Debye patterns of the compounds studied do not make it possible to refine the arrangement of atoms in the lattice. Table 3 gives the values of the lattice parameters of the compounds we obtained.

Table 3

Lattice parameters of SrSm₂O₄, SrDy₂O₄, SrYb₂O₄, BaSm₂O₄ (in angstroms)

Thus, strontium oxide apparently forms compounds with the oxides of most rare-earth elements (from samarium to ytterbium); analogous compounds should probably also be formed in the case of BaO, since the latter reacts with samarium oxide (the samarium ion has the largest radius in this group of elements). A further increase in the radius of the rare-earth element (the transition from Sm to La) leads to the disappearance of amphoteric properties (strontium oxide does not react with lanthanum oxide).

Moscow State University
named after M. V. Lomonosov

Received
26 IX 1963

References Cited

1. I. Sterba-Böhm, C. Melichar, Coll. Czechoslov. Chem. Commun., 7, 131 (1955).
2. W. I. Spitzen, L. N. Komissarova et al., Zs. Chem., 1, 328 (1961).
3. B. N. Ivanov-Emin, E. A. Ostroumova, ZhNKh, 5, 1921 (1960).
4. H. Bärnighausen, G. Brauer, Acta Crystallogr., 15, 1059 (1962).
5. B. E. Decker, J. S. Kasper, Acta Crystallogr., 10, 332 (1957).