Cristallite size and grain size are equal only if each grain is a monocrystal, a rare case. TEM images are needed to make a conclusion!
Cristallite size and grain size are equal only if each grain is a monocrystal, a rare case. TEM images are needed to make a conclusion!
a single crystal material has a single grain which means grain size is equal to crystal size.
As you can see above it is a matter of semantics: often, grain size and crystallite size are used synonymously to denote the volume (or rather, length scale) over which the crystal structure is continuous, and then of course they are equal.
Dear Nadir,
I think, the possibly of finding grains with same crystalline size increases as the size of crystalline increase.
A particle or grain may contain more than one crystallites. In a special case, when one grain contains only one crystallite, we can say that crystallite size is same as grain size.
Hi Prof. Habubi,
If you need some various actual cases, I think our product is one of them. The crystallite sizes of our products, metal NPs, are almost equal to the particle size (30-150nm). We check them by mainly SEM and XRD. We concluded the almost particles are monocrystal, using TEM images as Dr. Colomban said. Our synthesis technology is one of the flame vapor deposition tech. We form firstly metal vapor by exothermal reaction and oxy-fuel burner flame. The vapor cools and translates nanosized molten droplets. The molten droplets finally change to NPs.
Higher temperature, the crystal growth is more rapid. Therefore, I've heard CVD and Physical Vapor Deposition can also fabricate monocristal NPs.
Does that answer you, professor?
As already mentioned in some of the reply, I also think that the crystallite size and grain size are equal only if each grain is a monocrystal.
Crystallite size and grain size are different even though it is used in similar context in general. They may be equal when one grain has only one crystallite. Size measurements by XRD line profile analysis give crystallite size which may be confirmed by TEM to arrive a conclusion of crystallite/grain size.
A particle consists of one or more grains or crystallites. Grain and crystallite could be used interchangeably, yet you have to keep in mind that when you talk about crystallite or grain, you are talking about something which has the same crystallographic properties in addition to similar orientation the constituent crystals are arranged into all over the place; the crystallographic properties close to the boundaries of other grains or crystallites are somewhat following the properties of both neighbors.
I am a little bit confused by the answers. All these comments show the meaning of words is subjective.
What is the difference between a particle and a grain? In metallurgy, a grain is a domain where atoms are distributed in an order (single crystal) and each atom has the same environment.
But after the comments a grain would mean a particle.
In thin films there is no differentiation between grain size and crystallite size and the terms are used interchangeably...Actually the word 'crystallite' is used rarely but it has the same meaning in deposited films.
The grain size should have a high density of dislocations and (maybe crystallographic incoherence for random orientation). Then grain boundary diffusion coefficient may be up to 10^5 times larger than the mass diffusion coefficient, so both crystallographic and density criteria should make the difference. As such, metallurgical grain boundaries may be evidenced optically after some acid treatment of the surface (etching), while the crystallite may be measured from XRD line(Debye, Warren Averbach, Gangulee). TEM is too tedious given the magnification is too large and the average is difficult to obtain.
In case of films, the film may be thinner than the corresponding metalurgical grain size. The crystallite size may be estimated for films but metallurgical grains are not expected to form because of epitaxy.
In deposition of films, I observed that depletion of the film occured at the grain boundaries of the SUBSTRATE, but because of epitaxy no metallurgical grain, corresponding in size to the powder compund (less than the grain size of the "single crystal" substrate) was observed.
Please observe that the substrate had a definite role in defining the defect structure of the film. Substrate temperature and deposition rate also affected the DEFECT structure of the film. For superconducting Bi:2223 films, the most proeminent was terracing of CuO planes (3D conduction near Tc). Satellites of the (00l) were observed, which are currently modelled as a misalignment also (thin film theory of the '90s).
If we think very simple, the crystallite size and grain size are equal only if each grain is a monocrystal. But, when this can occur? In which condition? I think, when the all low angle grain boundaries disappears in the microstructure, the grain size will be equal to the crystallite size.
The answer is very old, since the beginning of XX-th century, when Darwin tried to develop the dynamic theory of XRD on single crystals.
A single crystal will give a very WEAK reflection given destructive diffraction inside-primary extinction. Primary extinction is very tricky.
Secondary extinction applies to large crystalline blocks in polycrystals. The term used for large coherent blocks (see Guignier 1955 in French) is "block" not "grain".
So, a large crystallite (larger than 3000A) should be "block"( not "grain"), presenting secondary extinction, i.e. attenuation of the XRD peaks at high angles (see Guignier).
"Crystallite size" for a powders is obtained in the kinematic theory of X- Rays by the methods of Debye(line breath deduced from th Brag's law), Warren-Averbach(pair of peaks) or Gangulee(sinle line variant of WA).
So, the question is not well formulated since we compare entirely different concepts. Kinematic theory involves that no dynamic effects are present(finely milled powder to prevent extinction effects).
To answer one of the previous participants, yes, to my knowledge grains are very similar to single crystals. In any case the orientation is definitely the same. In other words, crystallization from a liquid starts simultaneously at a number of preferential sites (usually the top surface and the walls) and crystallites grow until they meet their neighboring crystallite, so eventually each one of them becomes a grain and they meet at the grain boundary. In thin films the crystallization occurs in parallel at the surface and the grains may be overlapping, but if the film is thin this does not happen. The deposition method is of importance here, whether it's evaporation or sputtering or some plasma assisted method.
In thin films the small glancing angle is used (GIXRD), not powder, so I am not sure how this relates to the answer by Prof. Ciurchea.
Many aspects have been mentioned already. From my more metallurgical point of view, I would agree with the notion that grain and crystallite are often used synonymously. Subdividisions within a grain could be low angle grain boundaries or twin boundaries, but I would not understand these in the way that their existence within a grain constitutes a separation between crystallites. So from that point of view, a difference in size of crystallit and grain would be based on the association of a large angle grain boundary, which might not belong to either of the neighbouring crystallites, to the grain: If you count (maybe up to the middel) it as part of the latter, naturally the grain would exceed the crystallite in size.
At least for XRD, the largest crystallite shoud be 3000 Angstrom (0.3 microns). The metallurgical grains in that sample have sizes above 10 micrometers. Larger sizes involve that kynematic theory doesn't apply anymore and extinction effects are to be expected.
As a rule:"For large grains you should expect extinction:(secondary or primary)."
If we we talk about other definition of the crystallite size than that taken from the line breath of X-Ray diffraction on powders (polycrystals), the distinction between crystallite and grain is arbitrary.
For crystal wisker, the grain size is possibly the crystallite size. :)
It is impossible to get crystallite size is similar with grain size, eventhough the synthesis process involved precursor and optimum T/P/t. u may get better understanding in thin film and crystal growth technology.
After nucleation process if the growth of the crystal is properly controlled, there is chance of getting crystallite size equivalent to grain size.
One can confirm this by taking XRD (Average Crystalline size) and morphological characterizations like TEM (grain sizes)
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