Abstract Generated abstract
This paper reports the preparation and characterization of lanthanum ditelluride, LaTe2, a rare-earth metal ditelluride for which little prior information was available. Single crystals were obtained by a chemical transport reaction using powdered LaTe2 and iodine, with transport from 950 to 800°C over 100 hours, and were examined by chemical analysis and measurements of structural and physical properties. The crystals were black with metallic luster, mainly tetragonal pyramidal habits, and showed composition close to LaTe2 with no qualitative evidence of iodine contamination. The compound was found to be tetragonal, space group P4/nmm, with lattice parameters a = 4.55 kX and c = 9.16 kX, density about 6.8 g/cm3, n-type conductivity in single crystals, and stability in air under ordinary conditions.
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CHEMISTRY
A. A. ELISEEV, E. I. YAREMBASH, E. S. VIGILEVA
LANTHANUM DITELLURIDE LaTe$_2$
(Presented by Academician I. V. Tananaev, 22 VII 1963)
In the group of rare-earth metal chalcogenides of the MeX$_2$ type, the ditellurides are the least studied. In paper ($^1$) there is information on the formation of LaTe$_2$ single crystals in the process of a transport reaction of La$_2$Te$_3$ with iodine.
To obtain single crystals, we used a chemical transport reaction, using powdered lanthanum ditelluride LaTe$_2$ as the starting substance,
\[ 2\mathrm{LaTe}_2 + 3\mathrm{J}_2 = 2\mathrm{LaJ}_3 + 2\mathrm{Te}_2 \quad (950^\circ \to 800^\circ). \]
The work was carried out by the diffusion method; the initial concentration of the transport agent was 5 mg/cm$^3$; the duration of the experiment was 100 hours.
LaTe$_2$ single crystals of average dimensions $1 \times 2 \times 2$ (mm) were obtained; color—black, with a metallic luster; habit: truncated tetragonal pyramid; crystals of prismatic-pyramidal and pyramidal form are also encountered; twinning was noted. Results of chemical analysis of the single crystals:
Found, wt. %: La 35.7; Te 63.3; $\Sigma$ 99
Calculated, wt. %: La 35.24; Te 64.76; $\Sigma$ 100
The qualitative reaction for iodine is negative (Ag$^+$ test). The insufficient accuracy of the analytical data ($\pm 0.5\%$) is associated with the small size of the sample.
Table 1
Physical properties of lanthanum ditelluride
| Formula | Color | M.p., °C | Syngony | Space group | Parameter ($kX$) (20°C), $a$ | Parameter ($kX$) (20°C), $c$ | $Z$ | Density g/cm$^3$ (20°C), X-ray | Density g/cm$^3$ (20°C), pycn. | $\rho$ (20°C), ohm·cm | Conductivity | $x_r \cdot 10^{-6}$ (20°) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| LaTe$_2$ | Black | >1200 | Tetragonal | $D_{4h}^{7} = P4/nmm$ | 4.55 | 9.16 | 2 | 6.80 | 6.82 | $8 \cdot 10^{-2}$ | $n$-type | −0.03 |
The physical properties of LaTe$_2$ are given in Table 1. It is necessary to note that the initial powdered LaTe$_2$ possessed $p$-type conductivity. The study of the physical properties should be continued.
Under ordinary conditions, lanthanum ditelluride is quite stable in air.
Institute of General and Inorganic Chemistry
named after N. S. Kurnakov
Academy of Sciences of the USSR
Received
10 VII 1963
CITED LITERATURE
- P. Bro, J. Electrochem. Soc., 109, No. 11, 1110 (1962).