Physico-chemical interaction in the Ag₂Se–Zn(Cd, Hg, Pb)–SnSe₂ systems

The formation of quaternary compounds in the A^I₂X–B^IIX–C^IVX₂ systems where A^I–Cu, Ag; B^II–Zn, Cd, Hg; C^IV–Si, Ge, Sn; X–S, Se, Te is known for seven component combinations. The most common are the phases with the equimolar ratio of all three binary compounds described by the A^I₂B^IIC^IVX₄ formula. These quaternary compounds crystallize in non-centrosymmetric structures and may be of interest for nonlinear optics.

The boundary sides of the presented systems Ag₂Se–Zn(Cd, Hg, Pb)–SnSe₂ feature only two compounds, Ag₈SnSe₆ (Ag₂Se–SnSe₂ system) and Hg₂SnSe₄ (HgSe–SnSe₂ system).

The Ag₂Se–ZnSe–SnSe₂ and Ag₂Se–CdSe–SnSe₂ systems contain only one intermediate quaternary compound each, Ag₂Zn(Cd)SnSe₄, that form at the non-quasi-binary sections “Ag₂SnSe₃”–Zn(Cd)Se. The diffraction pattern of Ag₂ZnSnSe₄ was indexed in the tetragonal structure of the stannite type Cu₂FeSnS₄ (S.G. I2m) with the lattice parameters а=0.60434(2), с=1.13252(5) nm. The structure of the Ag₂CdSnSe₄ compound was determined in the orthorhombic symmetry, S.G. Cmc2₁. The Ag₈SnSe₆–Zn(Cd)Se sections of these systems are quasi-binary, of the eutectic type, with large solid solution ranges.

The Ag₂Se–HgSe–SnSe₂ system features at 670 K three intermediate phases, Ag₂HgSnSe₄, Ag₄Hg₃Sn₂Se₉, and Ag₆HgSnSe₆. Ag₂HgSnSe₄ crystallizes in the orthorhombic S.G. Pmn2₁. The Ag₄Hg₃Sn₂Se₉ compound crystallizes in the orthorhombic S.G. Imm2. This compound has a homogeneity region that is stretched to the ternary compound Hg₂SnSe₄. Тhe Ag₆HgSnSe₆ structure was not investigated.

No quaternary compounds were found in the Ag₂Sе–PbSе–SnSe₂ system. Ag₈SnSe₆–PbSe is the triangulating section in this system