Non-Crystalline Chalcogenides by M.A. Popescu

By M.A. Popescu

The earliest experimental information on an oxygen-free glass were released through Schulz-Sellack in 1870 [1]. in a while, in 1902, wooden [2], in addition to Meier in 1910 [3], conducted the 1st researches at the optical homes of vitreous selenium. The curiosity within the glasses that show transparency within the infrared sector of the optical spectrum rose before everything of the 20 th century. first of all have been investigated the heavy steel oxides and the transparency restrict used to be prolonged from (the case of the classical oxide glasses) as much as wavelength. that allows you to expand this restrict above the scientists attempted the chemical compositions according to the weather of the 6th staff of the Periodic desk, the chalcogens: sulphur, selenium and tellurium. The systematic study within the box of glasses in keeping with chalcogens, referred to as chalcogenide glasses, all started on the heart of our century. In 1950 Frerichs [4] investigated the glass and released the paper: “New optical glasses obvious in infrared as much as 12 . numerous years later he began the examine of the selenium glass and ready a number of binary glasses with sulphur [5]. Glaze and associates [6] built in 1957 the 1st technique for the coaching of the glass on the commercial scale, whereas Winter-Klein [7] released experiences on a number of chalcogenides ready within the vitreous state.

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13. The structure of orpiment viewed in two projections. (the figures indicate the position of the atoms above the plane of the paper) Currently, the structures are described in terms of pyramidal configurations Thus, in six pyramids are inter-linked by the intermediary of sulphur and form a ring. The arsenic atom is situated in the top of the pyramid while sulphur atoms, which link pairs of neighbouring arsenic, form its base. The bond angles in the pyramid are 99°. 26 CHAPTER 1 As opposite to in exists two kinds of pyramids with different distances to the first order neighbours and different valence angles on arsenic.

Finally, it is important to remark that, due to the metallic-like properties of SnTe the absence of glasses in the system Sn-Te receives a simple explanation. 6. 1. THE CHALCOGENIDES BASED ON HEAVY ELEMENTS The Systems Tl-Ch In the system thallium-sulphur (Tl-S) the phase diagram suggests the existence of the compounds TlS and crystallises in the hexagonal system, exhibits a monoclinic structure and is characterised by chains of tetrahedra linked by ions. TlS and have tetragonal symmetry. In the TlS structure no direct Tl-Tl bonds exist.

All Si-Ch compounds hydrolyse in humid atmosphere and form and Ch. In the system Si-S the glasses are prepared with difficulty. The glass is difficult to get because the temperature range for the existence of the melt is very narrow (1090-1130 °C). Glasses have been obtained in the composition interval when the samples were melted under pressure (25-80 kbar) and rapidly cooled [91]. The silicon chalcogenide glasses are much more stable in humid environment than the crystalline compounds. % Se. The structure of these glasses has been explained by Johnson et al.

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