Phase equilibria in the Tl2SPbSGeS2 system and crystal structure of Tl0.5Pb1.75GeS4

 

Chem. Met. Alloys 5 (2012) 37-41

 

M.Yu. MOZOLYUK, L.V. PISKACH, A.O. FEDORCHUK, I.D. OLEKSEYUK, O.V. PARASYUK

 

The phase equilibria in the quasi-ternary system Tl2SPbSGeS2 at 520 K were investigated by XRD methods. Three intermediate quaternary phases were discovered, Tl2PbGeS4, ~Tl2PbGe3S8 and Tl0.5Pb1.75GeS4. The crystal structure of the quaternary phase Tl0.5Pb1.75GeS4 was determined by powder XRD in the non-centrosymmetric space group I-43d, Z = 16 and a = 1.420082(6) nm (Ag0.5Pb1.75GeS4 structure type). Atomic parameters were refined in the isotropic approximation (RI = 0.0496, Rp = 0.0944). The phase diagram of the Tl2GeS3PbS section was investigated. The section is quasi-binary, of the eutectic type, with formation of the equimolar compound Tl2PbGeS4, which melts incongruently at 781 K and undergoes a polymorphous transformation at 688 K. The -modification crystallizes with a monoclinic structure (S.G. P12/a1,  = 0.89079(7), b = 0.90951(7), c = 1.04772(7) nm, β = 94.116(7)).

 

 

Fragment of the Tl0.5Pb1.75GeS4 structure where Ge-centered tetrahedron is surrounded by the atoms of metallic components, and mutual positions of the thermal ellipsoids of atoms

 

Keywords

Thallium chalcogenides / Crystal structure / Phase diagram / Isothermal section