The liquid to glass transition occurs due to the critical slowing down of the dynamics of molecules with a decreasing temperature, resulting in the “kinetic-arrest” or “kinetic-freezing” of the high temperature liquid phase. Thus, it ceases the homogeneous nucleation of the super-cooled liquid into crystalline solid and consequently results in a liquid to “Glass-transition”.
First order phase transitions of any kind allows this type of situation. If first order phase transitions between the crystalline phases are kinetically frozen in such a situation, a high temperature crystalline phase will get frozen at the lowest temperature.
What should we call the unstable frozen phase below this freezing temperature:
(1) Glassy
(2) Super-cooled
(3) A new meta-stable phase?
@ Kai Zhao: Thanks for your comment. I feel you mean frustrated crystalline phase, as I am talk about frozen crystalline phase.
@Syed Shahee: Generally speaking, one of the ultimate goal of condensed matter physics is to find a Gibbs potential that can describe both liquid and solid correctly. This function should have a singular solution at the melting point (i.e. freezing point), corresponding to the first order transition.
Up to the mimute, the potentials for MD calculation are still constructed by first-principles or experimental data fitting. So it will be interesting to find a thermodynamic potential as a function of pressure and temperature.
It is really hard to obtain an exact quantum discrimination for the structure of materials near the melting curve. From the aspect of lattice dynamics, Lindemann once gave a classical melting law. He thought the solid will become liquid when the amplitude of atom exceed one half of the equilibrium lattice constant.
Your question has inspired me to ask another question: How to describe the materials structure just at the solid-liquid boundary?
@Paolo Ghigna : Sir can you explain in detail why it should be called simple Meta - stable crystal phase and not a Glassy state.(i.e what are the hindrance to call it a glassy state of crystal)
From your question, I understood that you were referring to a transition between two crystalline phases. If the undercooled metastable phase has a sharp diffraction pattern, then it is not a glass, it is a crystal.
@Paolo Ghigna: Sir as you know, the term “glass” is often loosely taken as synonyms of the “structural disorder” but the most widely accepted definition is the liquid in which the molecular motion has been freezed. Thus according to most widely accepted definition of glass (i.e. kinetically freezed state of matter) frozen crystalline phase should also be called a type of glass state. . I think so, and kindly correct if I am wrong.
A glass is structurally a liquid. If you take a diffraction pattern of a glass it will give you just diffuse scattering, and no Bragg peaks. If you are referring to crystal phases, i.e. to something that gives sharp diffraction effects, then you are dealing with crystals.
@Paolo Ghigna: Sir thanking you for your comment and for sharing you knowledge. So according to you disorder is one of the main criteria for a glassy state. Hope you will continue to share your knowledge in future with us.
Sir what I think is that:
If vetrification of state turns out to be a relaxation process and obeys kinetic rather that thermodynamic laws or in other ways at vitrification the structure of the substance freezes in under conditions where molecular rearrangements are so slow that a change of structure can’t keep up with changes in external parameters. Then the state which show kinetic dependent relaxation is called as glassy state. Unfortunate this state was initially observed during the liquid to crystal phase transition and the phase which got freezed was a liquid ( where atoms/ ions/ molecules are in disorder form) and there after we start to feel that freezed disorder system is called a glassy state.
Sir if I am wrong then please kindly correct it.
Take for example zirconium oxide. In this case, you have three crystal phases: with increasing temperature, the stability range is: monoclinic, tetragonal and cubic. That is, the cubic high tempetature phase has no structural degress of freedom (every atom is in a special position) and then you can call it "less disorderderd" (very roughly speaking) than the monoclinic room temperature phase.
@Syed Shahee: as far as i get what you're asking for, there is not much new in meta-stable and semi-crystalline states, which is normal case for polymers. It appears to be, that homogeneous crystal nucleation rate have maximum around glass transition temperature. At this temperatures long polymer chains have poor mobility and can hardly rearrange into crystals.That means, in some range of cooling rates we can freeze in tiny crystal surrounded by amorphous material (semi-crystalline state). These nuclei or crystals are so tiny and imperfect that it might be difficult to obtain any peaks in scattering. But it's easy to find them on heating - by extensive growing as soon as temperature rises above Tg (look for cold crystallization).
Hope it was helpful.
@ Evgeny Zhuravle and Paolo Ghigna: Sir thanks for you nice and informative comments. Actually my question in simple way is:
When kinetics become a hindrance during the liquid to crystal phase transition, the frozen liquid is called as glass....if now kinetic become a hindrance during the crystal to crystal phase transition, then what should we call this frozen crystal phase?
As you have stated in your reply, "...the most widely accepted definition is the liquid in which the molecular motion has been freezed". The key word here is "liquid", not "frozen". A crystalline phase is not at all liquid-like and should not be called a glass. A crystalline phase (in theory) has long range order and should not be referred to as a glass, no matter how this phase was prepared.
As an analogy, consider the pyrochlores Ho2Ge2O7 and Dy2Ge2O7 (http://www.nature.com/ncomms/journal/v2/n9/full/ncomms1483.html). These are prepared using a high-pressure method - if the starting reagents are heated under ambient pressure, the pyrogermanate phase results (http://arxiv.org/abs/0802.0424). Both phases are crystalline, but only one of them has been made via kinetic arrest. The pyrochlore is metastable.
@ Paolo Ghigna and Harlyn Silverstein: So according to both of you the system should be called "kinetically frozen meta-stable crystalline phase" and not "glass" or "glass-like" state.
Am I correct?
If the frozen phase has a definite diffraction pattern, then is a crystal and not a glass
Thank you dear Evgeny Zhuravle, Harlyn Silverstein and Paolo Ghigna for you informative comments.
Best regards to all
Paolo Ghigna and Harlyn Silverstein are on the mark IMO. A glass is basically a liquid that flows extreeeeeeeemly slooooooowly. If the material lacks order, but the atoms are kinetically locked into place, it's glassy.
@Karl Sohlberg: frist of all thanks for your nice comment.
I have one question related to the topic. If in a crystalline material, atoms are kinetically locked into place, should we call is a new phase of glassy state.
i.e. If a crystalline material is cooled below its superpercooling temperature and some how, the thermodynamically allowed phase transition is blocked by slow down its kinetics.should this kinetically frozen crystalline phase be called a phase of glassy nature.
Dear Syed, I wish to precise some of your claims :
1) It is not always possible to quench the high temperature phase in ANY first order transition : for instance, a martensitic transiton cannot be prevent by quenching; in fact, only thermally activated processes can be quenched, like diffusion.
2) Nucleation-and-growth process is only possible in first order transitions; however, the nucleation is rarely homogeneous; it must be maintained as homogeneous as possible to attain a glassy, or amorphous state (which you describe well), and which also is said metastable. There can be several metastable or glassy states, according to the kinetics of freezing down (and the maintaining of homogeneity); however, it is not, in my opinion, a supercooled phase : this latter would be nothing else than the quenched high temperature phase.
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