The phase diagram of the quasibinary system Hg3Se3/Ga2Se3

Abstract

The quasibinary system Hg 3 Se 3 /Ga 2 Se 3 was investigated by X-ray phase analysis and by DTA. The system forms extended regions of solid solutions with zincblende structure. Moreover, it shows at several distinct stoichiometries the formation of superstructures. The phase diagram of this system can be modeled by a Gibbs energy function for a sub-regular system including ordering terms. The thermodynamic factor for interdiffusion was calculated from the excess Gibbs energy function.

The phase diagram of the quasiternary system Ga2kHg3−3kSe3lTe3−3l

“…1 shows the overall compositions of all quasiternary samples that were prepared from the binary components to detect the one-and two-phase regions. The methods of preparation are described in [2][3][4].…”

“…As this is a superstructure of the zinc-blende lattice, a so-called pseudo-cubic lattice constant, defined by a * = (a 2 c/2) 1/3 , will be attributed to this lattice. Considering the composition dependences of the lattice constants for the quasibinary edge systems Ga 2 VSe 3l Te 3 − 3l [2], Hg 3 − 3k Ga 2k V k Se 3 [3], Hg 3 − 3k Ga 2k V k Te 3 [4], Hg(Se l Te 1 − l ) [5] and including the cubic and pseudo-cubic lattice constants of the quasiternary samples, as determined for the present paper, the composition dependence of the lattice constant in the quasiternary system can be described by a (k, l)/pm = 645.94 − 57.16k − 8.03k 2 + 9.62k 3 − 10.72kl + 14.30k 2 l − 11.36k 3 l − 37.44l.…”

“…In previous papers [3,4,6,10] it was shown that in quasibinary systems for each stoichiometric composition k * , where superstructures are formed, these ordering terms can be described by a function of the Gaussian type:…”

“…α (J/mol) α (J/mol) β (J/mol) τ (J/mol) (Ga 2k V k Hg 3 − 3k )Se 3 [3] Table 3 Ternary parameters R G 0 (J/(mol K)) Tr G 0 extr (J/mol) l extr 40,000 50 0.75 Fig. 6a shows that, for this case, the miscibility gaps are restricted to the neighborhood of the ordered region and that the chalcopyrite phase extends from the telluride edge up to the selenide edge of the phase square in contradiction to the experiments.…”

“…only two-thirds of the cation sites of the zinc-blende lattice are occupied by Ga. Including these structural vacancies as V into the formulas, the two quasibinary edge systems with a mixed cation sublattice have to be written as (Ga 2k V k Hg 3 − 3k )Se 3 [3] and (Ga 2k V k Hg 3 − 3k )Te 3 [4].…”