They are both formed when a liquid is supercooled rapidly, no free energy, and they both have irregular structures. What defines a glass other than how it is amorphous, transparent, and has a glass transition state?


While a glass is generally considered to be a supercooled, configurationally frozen liquid, not all amorphous solids are glasses. For example, amorphous silicon is a four-fold coordinated semiconducting solid, much like crystal silicon. Liquid silicon is 8-12 fold coordinated with metallic bonding. Amorphous silicon has been shown to display a first-order phase transition to both the crystal and the liquid.

So, all glasses are amorphous solids, but not all amorphous solids are glasses.

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    $\begingroup$ So how can you tell the difference between glass and a supercooled liquid or any other amorphous solid? $\endgroup$ – la.vie.en.rose Jun 21 '15 at 18:30
  • $\begingroup$ The supercooled liquid will have an x-ray diffraction pattern similar to the liquid. The amorphous solid may be different, and will be different if it is not a glass. Note above the difference in coordination number between metallic silicon and semiconducting crystal or amorphous. The first order phase transition from amorphous to crystal solids is shown in calorimetry. $\endgroup$ – Jon Custer Jun 22 '15 at 2:22
  • $\begingroup$ While I am going to give this an upvote, I do object to "glass is generally considered to be a supercooled, configurationally frozen liquid" although I think it is technically (statistically) true, if a million people say a foolish thing it is still a foolish thing. $\endgroup$ – A.K. Mar 22 '19 at 0:49
  • $\begingroup$ @A.K. - fair enough, and that could also be sub field specific. The sub field I was in some time ago (dealing with amorphous silicon amongst other materials) agreed on that distinction. $\endgroup$ – Jon Custer Mar 22 '19 at 1:34
  • $\begingroup$ @A.K. when objecting to something it makes sense to explain in detail why one is objecting and the counter-reasoning if possible ;) $\endgroup$ – Thomas Dec 20 '19 at 7:50

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