Chalcogenide glass

Chalcogenide materials behave rather differently from oxides, in particular their lower band gaps contribute to very dissimilar optical and electrical properties.

They are fragile glass-formers: by controlling heating and annealing (cooling), they can be switched between an amorphous (glassy) and a crystalline state, thereby changing their optical and electrical properties and allowing the storage of information.

Most stable binary chalcogenide glasses are compounds of a chalcogen and a group 14 or 15 element and may be formed in a wide range of atomic ratios.

A most recent and extremely comprehensive university study of more than 265 different ChG elemental compositions, representing 40 different elemental families now shows that the vast majority of chalcogenide glasses are more accurately defined as being predominantly bonded by the weaker van der Waals forces of atomic physics and more accurately classified as van der Waals network solids.

They are not exclusively bonded by these weaker vdW forces, and do exhibit varying percentages of covalency, based upon their specific chemical makeup.

This makes them useful for encoding binary information on thin films of chalcogenides and forms the basis of rewritable optical discs [3] and non-volatile memory devices such as PRAM.

In addition to memory applications, mechanical property contrast between amorphous and crystalline phases is an emerging concept of frequency tuning in resonant nanoelectromechanical systems.

[8][9] Although the electronic structural transitions relevant to both optical discs and PC-RAM were featured strongly, contributions from ions were not considered—even though amorphous chalcogenides can have significant ionic conductivities.

Thus, a unified approach to the study of chalcogenides, assessing the collective roles of atoms, ions and electrons, may prove essential for both device performance and reliability.