Klymovych O. Phase equilibria and glass formation in the Cu(Ag)2Se – Ge(Sn)Se2 – As2Se3 systems

In the dissertation work the phase equilibria, crystal structure of intermediate phases, glass formation and properties of glass in Cu(Ag)2Se – Ge(Sn)Se2 – As2Se3 systems were studied by means of methods of differential-thermal, X-ray phase, X-ray structural and microstructural analysis, measurement of microhardness, absorption spectra and THG signal. The original results of the work are 4 isothermal sections of the Cu(Ag)2Se – Ge(Sn)Se2 – As2Se3 systems at 513 K, 6 phase diagrams and 11 vertical sections of the Cu(Ag)2Se – Ge(Sn)Se2 – As2Se3 systems, 3 liquidus surface projections of the Cu(Ag)2Se – Ge(Sn)Se2 – As2Se3 systems onto the concentration triangle, re-investigated phase diagram of the Ag2Se – As2Se3 system. Fields of the primary crystallization of phases, types and coordinates of mono- and invariant equilibria were determined for the first time. For the first time, the existence of a new quaternary compound Ag2SnAs6Se12 and the crystal structure of the AgAs3Se5 і Ag2SnAs6Se12 compounds was investigated using X-ray powder method. AgAs3Se5 crystallizes in S. G. R m, the structure type of its own, a = 0.38195(1) nm, c = 5.0082(2) nm. Ag2SnAs6Se12 crystallizes in S. G. R m, the structure type of its own, а = 0.38124(2) nm, с = 3.9733(3) nm. Glass formation regions in the Cu2Se – Ge(Sn)Se2 – As2Se3 and Ag2Se – SnSe2 – As2Se3 systems were determined by quenching from 1073 K for the first time and the characteristic temperatures of the obtained vitreous samples were determined; the optical properties (spectral distribution of the absorption coefficient, temperature dependence of the absorption coefficient) and nonlinear optical properties of glasses (temperature dependence of the third harmonic generation (THG)) of the Cu2Se – GeSe2 – As2Se3 system were studied. On the basis of experimental data the peculiarities of the interaction of components and peculiarities of glass formation in the investigated systems Cu (Ag)2Se – Ge(Sn)Se2 – As2Se3 and related ones are determined, and also the peculiarities of the crystal structure of the investigated compounds are highlighted.