Hi All,
It would appear that there is no clear definition of what represents amorphous material (and this does not seem to have changed over some decades!) with commonly encountered definitions including:-
“The term, amorphous solid, must be reserved for substances that show no crystalline nature whatsoever by any of the means available for detecting it” (Klug & Alexander, 1974)
“Crystalline materials are frequently characterized as solids with fixed volume, fixed shape, and long-range order bringing about structural anisotropy, producing sharp diffraction peaks. Amorphous (or non-crystalline) materials are thus solids with fixed volume, fixed shape, characterized by short-range order, which, however, may also have loose long-range order” (Pecharsky & Zavalij, 2009)
With the advent of so-called nano-technology, the boundary has become even more flexible (especially when applying for grants from funding bodies!).
So my definition is "Decide on an arbitrary grain size (3nm seems to be popular) - if anything below this is amorphous, then the rest is crystalline"
Cheers
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Ian Madsen
Team Leader - Diffraction Science
CSIRO Process Science and Engineering
Box 312, Clayton South 3169
Victoria, AUSTRALIA
Phone +61 3 9545 8785 direct
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-----Original Message-----
From: Support and use of X-ray diffraction instrumentation [mailto:[log in to unmask]] On Behalf Of Matt Gave
Sent: Tuesday, 12 July 2011 12:06 AM
To: [log in to unmask]
Subject: What is "crystallinity"?
Hello All,
It seems that it is very common to talk about "crystallinity" in terms of a well crystallized material dispersed in a non-crystalline one. It is also reasonable, of course, to use the term "crystallinity" to refer to the crystal quality of a homogenous material. Is anyone aware of methods or references that discuss differentiation of these possibilities from XRD (or other) types of data? What if one has a mixture of a very highly defective semi-crystalline material in an amorphous one?
"Crystallinity" possibility 1:
Highly crystalline material dispersed in a vitreous one (2 materils)
"Crystallinity" possibility 2:
Homogenous but highly defected semi-crystalline material (1 material)
"Crystallinity" possibility 3:
Highly defected semi-crystalline material in a glass (two materials)
Any thoughts on how these possibilities are distinguished? Any leads on references?
Thanks in advance!
-Matt
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