Electrochemical Synthesis of LaSi2 from a NaCl-Naf-LaF3-K2SiF6 Melt at 1023 K

Abstract

Lanthanum silicides (La5Si4, La5Si3, La4Si, LaSi and LaSi2) are metal-like compounds with semiconductor properties. If this were true, it could become technologically important as an infrared detector material [1]. The possibility of electrochemical synthesis of lanthanum silicides from molten salts were investigated in this work. It can be concluded from thermodynamic calculation that silicon discharge from molten salts more positive than La (~ 0.8 V), in this case electrochemical synthesis possible only in two step, first deposited of Si, next step deposition of La onto Si with formation of lanthanum disilicide: I. 2Si + La(III) +3 e = LaSi2 ΔE0 10233 K = ΔG0 1023 K/ (nF) ≈ 0.500 V,where ΔE0 – is potential (V), ΔG0 - is the Gibbs energy of the reaction I. (J), n – is the number of electrons involved in the reaction (in our case, n = 3), F – is Faraday constant. The electrochemical behaviour of the molten salts system NaCl-NaF-LaF3-K2SiF6 was studied by cyclic voltammetry. A glassy carbon crucible served as a vessel for the melt and as an auxiliary electrode; a W wire was used as the working electrode; the measurements were made with respect to glassy carbon reference electrode 1023 K in argon atmosphere. Typical cyclic voltammogram for molten salts system NaCl-NaF-LaF3-K2SiF6 show two step process of electrochemical synthesis of LaSi2at 1023 K in Ar on W working electrode (Fig. 1 .). On the base of thermodynamic calculation and voltammetric investigation, it has been show that lanthanum disilicide can by electrochemical synthesized from a NaCl-NaF- LaF3-K2SiF6 melt at 1023 K in two step. References R.G. Long, M.C. Bost, J.E. Mahan., Appl. Phys. Lett. 5 3, 1272 (1988). Fig. 1. Voltammogram of a NaCl-NaF-LaF3- K2SiF6 melts on a W working electrode, v= 0.1 V/s. Figure 1