Consider a raspberry - made up of a bunch of primary particles with the overall surface area being the outside. The specific surface area (SSA) generally affects the activity of a catalyst in - halve the particle size and get 4 times the surface area and a predicted 4 times activity.  Small materials aggregate into larger cluster and agglomerates.  .. Search for a paper by me called 'Micron sized nan-materials'  The SSA and particle size are related by SSA = 6/D[3,2] where the D[3,2] is the Sauter Mean Diameter.  This may also be helpful and also the attached document

Nov 11th, 2008. Dispersion and nanotechnology

http://tinyurl.com/hpywsge

 A technique like DLS will probe the overall size (including coatings), BET surface area will look at the accessible surface, SAXS and SEM will probe the electron rich core and primary crystallite size.  ISO tends to prefer the term cluster because of the difficulty in terminology between aggregate (normally considered hard), agglomerate (soft; disrupted by sonication), and particle, primary particle, crystallite, grain etc..

Dear colleague Lebohang,

Crystallite Size is Different than Particle Size. A particle may be made up of several different crystallites or just one crystallite so in this case (particle size = crystallite size)

Crystallite size often matches grain size, but there are exceptions

Crystallites are coherent diffraction domains in X-ray diffraction.

Particles are chunks/pieces (usually very small, below 1 mm) of solid matter, ensembles of atoms. Particles can be as small as two atoms (the nitrogen particle for example, N2)

Grains are volumes, inside crystalline materials, with a specific orientation.

Particles can be polycrystalline, single crystal or amorphous. A 100 nanometer particle of gold, for instance, can be made of:

a single gold crystal,

many grains with a grain size

According to the literature, crystallite size is a measure of the size of coherently diffracting regions/domains of a material. Crystallite size is equal to grain size if the grain is perfectly single crystallite. However grains of sintered samples contains several dislocations and defects, which, which interrupt the periodicity of the crystalline nature so an individual grain may contain a number of crystallites defined as coherently diffracting regions. XRD technique provides the information of these crystallite (coherently diffracting region) size present in the grains. Whereas the microscopic examination using SEM provides the grain size/ particle size of the material. Since grain contains many crystallites (coherently diffracting region), the crystallite size and grain size are not same.

A particle can have many crystallites 

 A particle mad of many crystallites.

For most of the cases particle sizes are different from the grain sizes unless it is single crystal where particle size and grain size are same. Particle size is more relevant for amorphous materials. Catalysis, in general, greatly impacted by surface area which is related to particle size of the materials. Smaller the size of the materials, greater the surface areas. TEM can provide information about crystallite sizes, d values etc  ..

In the context of mineralogy, a crystallite refers to the microscopic size of a ‘single crystal’ of a mineral with a known distinct chemical formula and no grain boundaries. Whereas particles, on the other hand, are more often associated with microscopic mineral dust particles (~0.1-100µm) in the atmosphere from various sources such as mines and other industrial activity, volcanic eruptions, dust plumes from deserts. In this context, each particle can be made up of more than one mineral and can have grain boundaries, intergrowths, etc.

What about if some of you download the book of Guinier and Fournet " Small Angle Scattering of X-rays" kindly posted free-of-charge at:  http://stoa.usp.br/fluidoscomplexosic/files/2415/20510/Guinier,+Fournet,+Small+Angle+Scattering+of+X-Rays+(1955).pdf

and then goes for a quick reading of Chapter 5 entitled:  Comparison of the Results from Small-Angle Scattering with the Results of Other Methods of Measurement of Small Particles.

It was soon very helpful to me!

Thanks

Is it true that:

For single crystal all crystallite size, grain size and particle size are same.

for other materials:

crystallite size < grain size < particle size?

I agree with Ahmad answer and simply tells particle size means to measure the whole unit of the cell and crystalite size means to measure the inner boundaries in a single particle. Normally crystalite size is less than the particle size.

Best Wishes

I agree with Ajeet Kumar

Jason Morales (Referred)

https://www.researchgate.net/post/What_is_the_difference_between_crystallite_size_grain_size_and_particle_size

"I am a materials engineer. I densify nano-powders into large (coin-sized), fully dense bulk materials with a retained nanoscale microstructure. Let me share with you the distinction I make between these terms.

CRYSTALLITE and GRAIN are both SINGLE CRYSTALS.

A CRYSTALLITE is a single crystal in POWDER form.

A GRAIN is a single crystal within a BULK/THIN FILM form.

A PARTICLE is also thought of as an AGGLOMERATE. Small enough in size to not consider it as a bulk or thin film, but composed of 2 or more individual crystallites. Usually our group refers to a single body in a powder as a PARTICLE if we aren't sure about more specific details about its makeup.

When presenting SE micrographs in our group of our starting powders, we often initially report the particle size, because we can't accurately determine whether the particle is one crystal or composed of many compacted single crystals. Then after XRD or TEM analysis we can usually say whether each particle is an agglomerate composed of smaller crystallites (average crystallite size = X) or whether each particle is a single crystallite. And finally, when we present SE micrographs of fracture surfaces of our bulk samples, we definitely make references to average GRAIN size".

The structure of both will be same or different ?

Grain size usually refers to the average diameter of the individual crystal orientations found in poly-crystalline materials. Grain size and orientation has a large role in determining the properties of many materials, and is generally one of the most fundamental metrics in metallurgy.

Particle size refers to (again generally) the average diameter of a discrete piece of material, rather than a region in a material with a distinct crystal orientation. Generally particle size ends up referring to things like powders or inclusions. An inclusion is different than a grain because it is often an entirely different material which may or may not be undesired.

Crystallite size I actually had to double check, as it's not a term I hear generally. Technically grains and crystallites are the same thing, however I have mostly heard it used in reference to plastics. In some long chain polymers the chains can stack up in orderly rows rather than the usual spaghetti mess, forming local regions of crystalline order. Different fields and institutions tend to develop their own preferred words over time, so my experience with the word crystallite may not be universal.

Ah, yes, I know where this confusion comes from, it is “normal”, don’t worry.

-Crystallites are coherent diffraction domains in X-ray diffraction.

-Particles are chunks/pieces (usually very small, below 1 mm) of solid matter, ensembles of atoms. Particles can be as small as two atoms

-Grains are volumes, inside crystalline materials, with a specific orientation.

Particles can be polycrystalline, single crystal or amorphous

Particle size consist of several grains so particle size value is higher than grain size

yes by crystal lattice structure

Particle size consist of several grains therefore particle size value is higher than grain size

The simple answer can be as follow:

Particle (agglomeration of some grains) => Grain (ensemble of some crystallites and sometimes consists of a single crystalline material) => Crystallite (is the smallest and can be mono- or poly-crystalline)

One can consider crystallite and grain size to be approximately the same. It is important to note that a grain consists of a single material, but maybe crystalline, or polycrystalline. 

For a complete characterization, you may need to use a TEM with additional analytical tools. But you can distinguish single-crystal grains from polycrystalline grains by switch the mode to diffraction: a single crystal grain will form a sharp diffraction pattern associated with that material, the transform of the crystal structure, while the polycrystalline grains will have multiple copies of the pattern, perhaps even rings. When you get to the particle size, it is always the largest, and may consist of several grains, and perhaps even grains of different materials. You will spend some time with your local microscopists in order to complete the characterization. 

The average crystallite size can be determined using the Scherrer equation, the grain morphology is commonly determined by SEM, and the particle size can be estimated from TEM image.

Also please note that Sherrer's formula is an approximation, and works best for nearly spherical particles. You will obtain the best results from TEM or AFM, especially for very small, or irregular shapes.

A particle usually means a solid agglomeration which is apart from each other, has an interface with liquid or gas phase. It can consist of some atoms or molecules, one crystallite or many crystallites, and one grain or many grains. The crystallite is a single crystal has atoms in a near-perfect periodic arrangement. Particle size mainly affects catalysis, because the particle has a surface.

In structural metals, crystallite sizes are usually smaller than grain sizes. Some times crystals grow to large sizes in mm, but crystallite sizes are very small in nm. An example of ferritic steel weld shows that the crystallite sizes of the deposited W1 zone were 1.6 μm in 2θ=29° and 40 nm in 2θ=65° (200) by Scherrer’s method. The reference paper:

Article Fatigue and microstructure of welded joints of metal sheets ...

Lebohang Macheli

It's so simple, according to Peter Dier's Rule, Crystallite is smaller than grain, grain is smaller than particle.

Particle consists of grains and grain consists of crystallites. Hope you got it.

Thanks

In a poly crystalline material, there are large number of grains. Such grains are called crystallites. In each crystallite planea are oriened in a particular direction. In the case of single crystallite material, there is only one grain or crystallite. So in that case particle size and crystallite size are equal.

Particle is formed of several grains and grain is constructed thanks to the combination of several crystalites. 

Grain size usually refers to the average diameter of the individual crystal orientations found in poly-crystalline materials. Particle size refers to (again generally) the average diameter of a discrete piece of material, rather than a region in a material with a distinct crystal orientation.

Grain size is an average diameter of the individual crystal orientations in poly-crystalline materials. Particle size indicates diameter of a discrete piece of material, with a crystal orientation.

Crystallite size is the smallest - most likely single crystal in powder form. The crystallite size commonly determined by XRD.

Grain is either a single crystalline or polycrystalline material, and is present either in bulk or thin film form. During the processing, smaller crystallites come closer and grow to become larger due to kinetics. Therefore, in the most likely scenario, the grain is larger than a crystallite. And, the grain morphology is commonly determined by SEM (but not XRD).

Particle may be present as a single crystal or an agglomeration of several crystals. Therefore, particle is under no circumstances smaller than crystallite size. In the ultrafine nano regime, particle size and crystallite size may be the same. XRD and TEM are commonly employed to ensure that there is any difference between the crystallite size and particle size.

Regarding the size comparison between grains and particles, it is however difficult to say whether the grain is bigger or particle is bigger. Sometimes, particles are evolved from controlled agglomeration of small grains, and alternately grains may also be grown from smaller particles by annealing at a higher temperature.

Further, since the crystallite size and grain size depend on nucleation and growth kinetics during processing, they may be different for different materials because the temperature sensitivity and melting points are also different for different materials.

This comparison is different for different samples. Sometimes they are same but sometimes different. I have recently watched a video on this topic. It is very effective and easy to understand. You may find this useful - https://www.youtube.com/watch?v=hjUp2pkONRM

Lebohang Macheli Scherrer equation (D=Kλ/βcosθ) is used in XRD to calculate the crystallite size. In this equation, D average crystallite size, K is the Scherrer constant which is 0.68 to 2.08, 0.94 for spherical crystallites with cubic symmetry, λ is the X-ray wavelength, CuKα=1.5406 angstrom, β is the line broadening at FWHM in radians, and θ is the Bragg’s angle in degrees. In this and some other videos, I have explained what is a crystallite, a grain and a particle, and how to calculate it from XRD data. In the case you want to further ask about it, please do comment on the specific video, I'll respond to it shortly. I have provided the practice file (OriginLab) and the calculation file (Excel) here. Thanks

https://youtu.be/lZ1VESKBxKY

To get some feedback, please refer to the latest preprint article at link DOI: 10.13140/RG.2.2.27720.65287/3 or at link https://www.researchgate.net/publication/352830671

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Page 5 of a recently published article (https://doi.org/10.1007/s10854-023-10604-6) discusses some detail about the difference between tiny-sized grains, crystallite size, grain size, and particle size. A copy is uploaded automatically at the page https://www.researchgate.net/publication/371008415. Thank Springer Nature and ResearchGate for providing researchers accessing scientific content in new ways.