Quasi-ternary system Tl2Se-AgTlSe-TlBiSe2

The quasi-ternary system Tl2Se-AgTlSe-TlBiSe (A) has been investigated by DTA, X-ray powder diffraction, microstructural analysis, and microhardness measurements. Polythermal sections AgTlSe-TlBiSe2, AgTlSe-Tl9BiSe6, [Ag0.5Tl1.5Se]-TlBiSe2, Tl2Se-AgBiSe2 (0–50 mol % AgBiSe2), an isothermal section at 500 K, and the projection of the liquidus surface of system A have been constructed. It has been shown that the quasi-binary join AgTlSe-Tl9BiSe6 divides system A into two subordinate triangles, namely, Tl2Se-Tl9BiSe6-AgTlSe (B) and AgTlSe-Tl9BiSe6-TlBiSe2 (C). The phase diagram of subsystem B involves a univariant eutectic equilibrium while subsystem C involves an invariant eutectic equilibrium. The ternary eutectic has the coordinates 650 K, 10 mol % TlBiSe2, and 61 mol % AgTlSe. A continuous series of solid solutions (0–12 mol % AgTlSe) has been found along the Tl2Se-Tl9BiSe6 bordering system. The homogeneity region of TlBiSe2 extends to 5 mol %.