Фазовая диаграмма системы Li-Te

К оглавлению: Другие диаграммы (Others phase diargams)

Li-Te (Lithium-Tellurium) J. Sangster and A.D. Pelton The assessed Li-Te equilibrium diagram is based primarily on the thermal analysis and DTA of [73Cun]. Liquidus and isothermal transformation data were obtained with both heating and cooling cycles [73Cun]. Undercooling was a major problem in Te-rich samples [73Cun]. A eutectic was reported at 179.9 C. Because [73Cun] reported a melting point of pure Li 0.1 C below the accepted value, the eutectic temperature is given as 179.8 с 0.3 C in the assessed diagram. Under the assumption of negligible solid solubility of Te in (bLi), the thermodynamic freezing point depression equation then gives a eutectic composition of ~0.15 at.% Te. The slope of the liquidus at 100 at.% Te was calculated from the thermodynamic freezing point depression equation under the assumption of zero solid solubility of Li in (Te). The measured liquidus extrapolates to nearly the calculated limiting slope. The solubility of Li in ( Te) can thus be estimated to be <1 at.%. The compound Li2Te was prepared by direct combination of the elements [34Zin, 73Cun, 66Gru, 78Hit]. Its melting point was measured by DTA as 1201 C [73Cun], who also determined the melting point by direct visual observation as 1208 C. An average value of 1204 с 10 C has been adopted in the assessed diagram. The compound LiTe3 has been prepared by direct combination of the elements [ 73Cun, 78Hit] and from a Te + Li2Te mixture [77Val]. The melting point of LiTe3 was reported [73Cun] to be 459.9 с 0.7 C. [78Hit] reported that LiTe3 is thermodynamically unstable below 304 C. The decomposition (peritectoid) temperature has not been precisely measured. The presence of a liquid-liquid immiscibility region was postulated in the Li- rich part of the phase diagram by [73Cun], who ascribed DTA thermal effects at 812 с 3 C to a monotectic reaction; the width of the miscibility gap at this temperature was suggested to be ~8 to 24 at.% Te. However, [73Cun] did not rule out the possibility that the observed thermal arrests were caused by a Te- Nb corrosion product from reaction with the container material. Hence, the existence of the miscibility gap and the monotectic at 812 C is only very tentatively indicated. However, the very low solubility of Te in liquid Li at the eutectic temperature, 179.8 C, also suggests that the liquidus is either interrupted by a miscibility gap or is at least S-shaped. 34Zin: E. Zintl, A. Harder, and B. Dauth, Z. Elektrochem., 40(8), 588-593 ( 1934) in German. 66Gru: D.M. Gruen, R.L. McBeth, M.S. Foster, and C.E. Crouthamel, J. Phys. Chem., 70(2), 472-477 (1966). 73Cun: P.T. Cunningham, S.A. Johnson, and E.J. Cairns, J. Electrochem. Soc., 120(3), 328-330 (1973). 77Val: D.Y. Valentine, O.B. Cavin, and H.L. Yakel, Acta Crystallogr., B, 33(5), 1389-1396 (1977). 78Hit: B.F. Hitch, L.M. Toth, and J. Brynestad, J. Inorg. Nucl. Chem., 40(1) 31-34 (1978). Submitted to the APD Program. Complete evaluation contains 1 figure, 3 tables, and 12 references. Special Points of the Li-Te System