CHEMISTRY

A. A. MENKOV, L. N. KOMISSAROVA, Yu. P. SIMANOV
and Academician Vikt. I. SPITSYN

ON SCANDIUM CHALCOGENIDES

Scandium chalcogenides, with the exception of the oxide, have been completely unstudied. The literature contains only data on the preparation of scandium sesquisulfide Sc₂S₃ (¹) and scandium selenide Sc₂Se₃ (²). We have previously described methods of preparation and the crystal structures of scandium sesquiselenide (Sc₂Se₃) and scandium telluride (Sc₂Te₃) (³). In the Sc—Te system, in addition to Sc₂Te₃, a compound of composition ScTe was found, characterized by an individual set of interplanar spacings.

The present article gives the results of an X-ray study of Sc₂O₃, Sc₂S₃, and also scandium telluride of composition ScTe. In the Sc—S and Sc—Se systems, individual compounds of composition 1 : 1 were not found. Scandium oxide of purity \(> 99.9\%\), obtained from technical oxide by methods of rhodanide extraction and precipitation of scandium oxalate (⁴), was used for the investigation. Sc₂S₃ and ScTe were synthesized from the elements. Metallic scandium of 97—97.5% purity was obtained by reduction of anhydrous scandium chloride with metallic calcium (⁵). Sulfur, free of selenium, was first melted and purified by vacuum sublimation (\(10^{-4}\)—\(10^{-5}\) mm Hg) at 100—110°C. The purity of the sublimed sulfur was \(> 99.9\%\). Tellurium of purity \(>99.99\%\) was obtained from the technical product by double reprecipitation of tellurium dioxide (⁶) and by sublimation of preliminarily reduced and melted elemental tellurium in vacuum (\(10^{-4}\)—\(10^{-5}\) mm Hg) at 400° (⁷).

The synthesis of Sc₂S₃ and ScTe was carried out as follows. Metallic scandium and the corresponding chalcogen, taken in equivalent amounts, were thoroughly mixed and placed in quartz ampoules of about 10 ml volume, which were then evacuated to \(10^{-4}\) mm Hg and sealed. The weight of the mixtures was 3—5 g. The time of synthesis and annealing of the compounds was:

Sc₂S₃ and ScTe are unmelted crystalline powders, yellow and black in color, respectively.

X-ray photographs of samples of Sc₂O₃, Sc₂S₃, and ScTe were taken by the powder method with filtered CuK\(_\alpha\) radiation in RKD-57 and RKU-86 cameras. The line intensities were estimated visually on a five-point scale. The results of the X-ray analysis are presented in Tables 1, 2, and 3.

Table 1

Results of X-ray analysis of scandium oxide

\(a_{\mathrm{av}} = 9.835 \pm 0.005\) kX

Table 2

Results of X-ray analysis of scandium sulfide

* The origin of the line has not been established.

All lines of the scandium oxide photograph are satisfactorily indexed in a cubic body-centered lattice of the \(\mathrm{Mn_2O_3}\) type \(^{(8)}\) with \(a = 9.835 \pm 0.005\) kX, \(Z = 16\). According to literature data \(^{(9-11)}\), the lattice parameter of \(\mathrm{Sc_2O_3}\) is somewhat smaller: from 9.76 to 9.828 kX (see Table 4). The X-ray density of scandium oxide is 3.84 g/cm\(^3\); the pycnometric density is 3.75 g/cm\(^3\).

The lines of the scandium sulfide photograph, in intensity, are sharply divided into two categories: very strong and weak. The strong lines are indexed in a primitive cubic lattice with \(a_0 = 2.591\) kX, which is a subcell. The weak lines, however, are due to a superstructure. By analogy with the recently

Table 3

Results of X-ray analysis of scandium telluride of composition ScTe

Table 4

Some properties of scandium chalcogenides

With the established structure \(\beta\)-In₂S₃ \((^{12})\), for Sc₂S₃ we adopted a tetragonal face-centered lattice with \(a = 10.37 \pm 0.01\) kX \((a = a_0 \times 4)\) and \(c = 31.11 \pm 0.03\) kX; \(c/a = 3,\ Z = 32\). Indeed, of 24 weak lines up to angles \(\theta \approx 40^\circ\), 21 lines are satisfactorily indexed in such a tetragonal lattice. The presence of unindexed lines can be explained by the existence of another superstructure in scandium sulfide or by the presence of small amounts of foreign impurities. The X-ray density calculated for such a tetragonal lattice proved to be 2.96 g/cm³; the density of Sc₂S₃, determined pycnometrically with chloroform, is 2.80 g/cm³; according to the literature it is 2.85 g/cm³ \((^{1})\).

All 25 lines of the ScTe pattern are well indexed in a hexagonal lattice of the NiAs type with \(a = 4.112 \pm 0.005\) kX and \(c = 6.735 \pm 0.005\) kX, \(c/a = 1.634,\ Z = 2\). The X-ray density of ScTe is 5.75 g/cm³; the pycnometric density, found using bromoform, is 5.65 g/cm³.

The results obtained by us do not agree with the data of a recently published work \((^{13})\), in which it is indicated that ScTe crystallizes in a hexagonal lattice with \(a = 6.728\) Å and \(c = 8.360\) Å. The type of crys-

of the gallic lattice \(Z\), and the density of ScTe is also not reported in this work.

The properties of the scandium chalcogenides currently known are presented in Table 4. It should be noted that the color of the compounds changes regularly from white to black in accordance with the increase in the polarizability of the chalcogen, and the crystal lattices of all scandium chalcogenides are characterized by high symmetry.

Moscow State University
named after M. V. Lomonosov

Received
24 VI 1961

CITED LITERATURE

1. W. Klemm, K. Meisel, H. Ulrich, Zs. anorg. Chem., 190, 123 (1930).
2. W. Klemm, A. Koczy, Zs. anorg. u. allgem. Chem., 233, 84 (1937).
3. A. A. Men’kov, L. N. Komissarova, Yu. P. Simanov, Vikt. I. Spitsyn, DAN, 128, No. 1, 92 (1959).
4. W. Fischer, R. Bock, Zs. anorg. u. allgem. Chem., 249, 146 (1942).
5. Vikt. I. Spitsyn, L. N. Komissarova, A. A. Men’kov, DAN, 139, No. 4 (1961).
6. A. S. Pashinkin, A. A. Men’kov, A. V. Novoselova, ZhNKh, 2, 826 (1957).
7. A. V. Novoselova, A. S. Pashinkin, A. A. Men’kov, A. E. Tolochdenberg, Izv. Vyssh. ucheb. zav., Khim. i khim. tekhnol., 1, No. 6, 9 (1958).
8. W. H. Zachariasen, Zs. Kristallogr., 67, 455 (1928).
9. V. M. Goldschmidt, T. Barth, G. Lunde, Norske Videnskaps-Akademi i Oslo I. Matem. Naturvid. Klasse, 7, 5 (1925); Chem. Zbl., 1925, 2, 1127.
10. W. H. Zachariasen, Norsk geol. tidsskr., 9, No. 3—4, 7 (1927); Chem. Zbl., 1927, 2, 11.
11. H. E. Swanson, R. K. Fuyat, G. M. Ugrinik, National Bureau of Standards, Circular 539, 3, 1954.
12. C. J. Rooymans, J. Inorg. and Nucl. Chem., 11, No. 1, 78 (1959).
13. L. H. Brixner, J. Inorg. and Nucl. Chem., 15, No. 1/2, 199 (1960).