What defines a chalcogenide glass?

An amorphous solid containing S, Se or Te but not oxygen, with elements like As or Ge

A glass made only of oxygen and silicon

A polymer of carbon and sulphur

Why is the melt rapidly quenched during preparation?

To remove impurities by evaporation

Which property makes chalcogenide glasses useful for thermal imaging lenses?

Transparency to visible light only

Which application relies on switching reversibly between amorphous and crystalline phases?

Phase-change memory and rewritable discs using GST

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Short note: Chalcogenide glasses

Short answer

Chalcogenide glasses are amorphous solids containing S, Se, Te with As, Ge, made by melt-quenching. They are transparent in infrared, semiconducting, and photosensitive. Applications include IR optics, optical fibers, phase-change memory, and photoreceptors.

Write a short note on chalcogenide glasses.

Chalcogenide glasses are amorphous (non-crystalline) solids that contain one or more chalcogen elements (S, Se, Te; but not oxygen) combined with elements such as As, Ge, Sb, Ga or P. Examples: As₂S₃, As₂Se₃, GeSe₂, Ge–Sb–Te (GST), As–Se–Te.

Preparation: the high-purity elements are weighed in the required ratio, sealed in an evacuated silica ampoule and melted at 600–1000 °C with rocking for a homogeneous melt. The melt is rapidly quenched (cooled quickly in air or water) so that it solidifies as a glass instead of crystallising.

Properties: transparent in the infrared (about 1 to 15 µm), high refractive index, semiconducting, photosensitive, and can switch reversibly between amorphous and crystalline phases.

Engineering uses

Infrared optics: lenses, windows, thermal-imaging and night-vision cameras.
IR optical fibres for sensing and laser power delivery.
Phase-change memory and rewritable optical discs (CD-RW, DVD-RAM) using GST alloys.
Photoreceptor drums of photocopiers (amorphous Se, As₂Se₃); photoresists and solar cells.
Switching devices, chemical sensors and waveguides.

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