CHEMISTRY

N. I. Sevost’yanova, I. A. Murav’eva, L. M. Kovba,
L. I. Martynenko, Academician Vikt. I. Spitsyn

On New Compounds of the Oxides of Rare-Earth Elements and Lithium

The problem of the amphoteric character of the oxides of rare-earth elements has been discussed in the literature for quite some time. Recently a number of works have been published devoted to the study of the interaction of the oxides of rare-earth elements (r.e.e.), Ln, with the oxides of elements of the first and second groups of the periodic system. Thus, as a result of the interaction of lithium oxide with the oxides of certain r.e.e., compounds of the type LiLnO\(_2\) have been obtained \(^{1-6}\).

In the literature there was no information on the interaction of praseodymium and terbium sesquioxides with lithium oxide. The aim of the present work was to obtain compounds of praseodymium and terbium oxides with lithium oxide.

For this purpose the oxides Pr\(_6\)O\(_{11}\) and Tb\(_4\)O\(_7\) were first reduced with hydrogen at 600°. The completeness of reduction was monitored by X-ray phase analysis. A mixture of the sesquioxides Pr\(_2\)O\(_3\) (or Tb\(_2\)O\(_3\)) and lithium carbonate was thoroughly ground for two hours with alcohol; then the alcohol was evaporated, and pellets were prepared from the powder. The ratio Ln : Li in the mixture was respectively 1 : 1, 1 : 2, 1 : 3. The samples were calcined in a stream of hydrogen in corundum crucibles at 500, 600,

Table 1

Results of indexing the X-ray pattern of LiTbO\(_2\)

700, 800°. The calcination time was 30 h. Powder photographs of the calcined samples were taken in an RKD camera. For recording X-ray patterns of preparations containing $\mathrm{Pr_2O_3}$, Cu $K_\alpha$ radiation was used; for recording preparations containing terbium oxide, Co $K_\alpha$ radiation was used. The X-ray patterns of samples obtained at different calcination temperatures proved to be identical. The compound of lithium oxide with terbium oxide is isostructural with the previously described $\mathrm{LiGdO_2}$ ($^{4,6}$) and, consequently, has the formula

Table 2

Interplanar spacings for $\mathrm{LiP_2O_2}$

$\mathrm{LiTbO_2}$. Lithium terbate has a rhombic lattice. The lattice parameters of $\mathrm{LiTbO_2}$ are: $a = 5.27\ \text{Å}$; $b = 11.16\ \text{Å}$; $c = 3.41\ \text{Å}$. The results of calculating the X-ray pattern of $\mathrm{LiTbO_2}$ are given in Table 1. The compound of lithium oxide and praseodymium oxide has a lattice different from that of $\mathrm{LiTbO_2}$, which we were unable to index. Table 2 gives a set of interplanar distances

Table 3

Results of indexing the X-ray patterns of $\mathrm{LiLaO_2}$

characterizing the compound of $\mathrm{Li_2O}$ with $\mathrm{Pr_2O_3}$. On the X-ray pattern of the sample in which the ratio $\mathrm{Pr}:\mathrm{Li} = 1:1$, several weak lines of $\mathrm{Pr_2O_3}$ were present, evidently owing to the appreciable volatility of $\mathrm{Li_2O}$ under the synthesis conditions. Thus, it may be expected that the composition of the compound containing pra-

neodymium and lithium, can be expressed by the formula \(\mathrm{LiPrO_2}\). Under the same experimental conditions, a compound of lithium oxide with neodymium oxide, isostructural with \(\mathrm{LiPrO_2}\), was obtained. Calcination of a mixture of lanthanum and lithium nitrates with the ratio \(\mathrm{La} : \mathrm{Li} = 1 : 2\) in air at \(800^\circ\) for 10 h led to the formation of a new compound. The X-ray diffraction pattern of the sample was obtained in an RKV camera, Cu \(K\alpha\) radiation. In contrast to the data of \((^2)\), the compound obtained crystallizes in the orthorhombic system and has an orthorhombically distorted cubic cell. The method of homology was used in indexing the X-ray diffraction pattern. Lattice parameters: \(\mathrm{LiLaO_2}\) \(a = 11.540\) Å; \(b = 6.482\) Å; \(c = 3.840\) Å. Since the body-centered subcell must contain two heavy atoms, the true cell must contain six lanthanum atoms. The cell volume is \(287\ \text{Å}^3\); thus, the volume per lanthanum atom is \(47.8\ \text{Å}^3\), which is close to the half-sum of the volumes of lanthanum and lithium oxides \((53.5\ \text{Å}^3)\), i.e., \(Z = 6\) for the composition of the compound \(\mathrm{LiLaO_2}\). The results of indexing the X-ray diffraction pattern of \(\mathrm{LiLaO_2}\) are given in Table 3.

By calcining ytterbium and lithium nitrates, the compound \(\mathrm{LiYbO_2}\) was obtained, crystallizing in the tetragonal system. The lattice parameters calculated for this compound coincided with the data of \((^3)\).

Moscow State University
named after M. V. Lomonosov

Received
7 XII 1964

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