Remzi Aydın Use the search function within ResearchGate and you will find that this question has been posed (and answered) many times.

Grains and crystallite size may be comparable but not always. Crystallite sizes makes the coherent diffraction whereas a grain can consists of several crystallites.

The key difference between grain size and crystallite size is that grain size is the diameter of individual grains of sediment or lithified particles in clastic rocks, whereas crystallite size is the size of a single crystal inside a particle or gain. Grain size and crystallite size are important factors regarding solid materials. They have different definitions, measurement methods, as well as parameters.

In materials science, the terms "crystallite size" and "grain size" are often used interchangeably, but they do have different specific meanings:

• Crystallite size refers to the size of a single crystal in a polycrystalline material. In materials with a high degree of crystallinity, such as many metals and ceramics, the material is composed of many small crystals (crystallites) that are fused together. The size of these individual crystals can have a major impact on the material's mechanical properties. Crystallite size is often determined using techniques like X-ray diffraction (XRD).
• Grain size refers to the size of a grain in a polycrystalline material, where a grain is a region of the material within which the crystal lattice orientation remains consistent. In other words, a grain contains one or more crystallites, but all of the crystallites within a single grain have the same crystallographic orientation. When the crystallographic orientation changes, you've crossed a grain boundary into a new grain. Grain size can affect the material's mechanical and physical properties and is often measured using optical microscopy.

To put it simply, if a material's grain boundaries coincide with the boundaries of its crystallites (i.e., each grain is a single crystal), then the crystallite size and grain size are effectively the same. However, if a grain contains multiple crystallites (i.e., the crystallites are smaller than the grains), then the crystallite and grain sizes are different.

You may find the following references useful for further reading:

Remember that while the two terms are often used interchangeably in casual conversation or in certain contexts, they do refer to different concepts, and using them correctly can help avoid confusion.

They convey same meaning. However, if you measure crystallite size using powder XRD you should mention if it is area weighted or volume weighted crystallite size. If you measure the same using SEM or TEM, crystallite size and grain size convey same meaning.

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.

A grain can be formed by multiple crystallites while a crystallite is the smallest single crystal with a single orientation of planes

Dear Remzi Aydın,

This figure I show to my stdents:

Micicroscope deal with full view of particle.

Wide angle X-ray deal with CSR (coherent scattering region) - it may be differ for each cryst direction - usuall it is less than gran size.

SAXS (small angle X-ray scattering) deal with hyration radii - analog inertion radii.

Dear Michael E. Bolko,

You are talking about area weighted crystallite size achievable using Warren-Averbach method or Variance method. But there are other crystallite sizes namely volume weighted and direct crystalliite size obtainable using TEM.

Prabal Dasgupta

Dear Prabal Dasgupta,

Do you want me to present a lecture on comparative analysis of methods here?

Since I am a specialist in the field of x-ray research, I answered Remzi Aydın in such a way that he, if he is interested, familiarizes himself with the X-ray topic and draws conclusions.

But I am ready to give an invited lecture after my holidays this autumn at your Jimma University with a bias towards SAXS..

I have just retired. If you are interested I may contact my old Colleagues,

Prabal Dasgupta

Crystalite size refers to the size of individual crystals within a material, while grain size refers to the size of individual grains within a polycrystalline material. Both factors are important in determining the properties of materials, but they represent different aspects of the microstructure.

Thank you.

Grain size refers to the dimensions of larger areas made up of many crystallites. Crystallite size relates to the dimensions of individual crystallites inside a material.

Grain size refers to the volume of a material within which the crystal structure and the orientation of the crystals are the same. Grain is either a single crystalline or polycrystalline material, and is present either in bulk or thin film form.

Crystallite size is the smallest - most likely single crystal in powder form. The crystallite size is commonly determined by XRD. Particle is under no circumstances smaller than crystallite size. 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.

First of all, it is necessary to distinguish the difference between monocrystallite/single crystallite and polycrystallite. From this, a crystallite can be understood as a perfect single crystal. Hence, it will be found that the crystallite size is attributed to a perfect monocrystal, while a grain can contain many perfect monocrystals. Therefore, it is generally not possible to substitute grain size for crystalline size. In special cases, a grain can be just a single crystal. In that case, crystallite size is equivalent to grain size. Then, in a material containing a small amount of grains, the rest being the matrix, the grains can be surrounded by a large region of the matrix - The grains become isolated. In a material with a granular structure (such as corrugated iron or steel bars), the grains are in contact with each other and are separated by so-called grain boundaries (this is where crystalline defects, or impurities, are concentrated).

crystallite size is like single crystal in powder form.

grain size is either single crystalline or polycrystalline material and present in either powder or bulk form

Grain size is calculated through FESEM or SEM images but the crystallite size(D) is determined through XRD both are not same

The crystallite size depends on the continuity of the crystal structure's long-range ordering and is obtained by XRD.

The grain size depends on several united crystals with different orientations in the long-range ordering of the crystalline structure and can be obtained by TEM and SEM.

Crystallites refer to small regions within a material where atoms or molecules are arranged in a highly ordered, periodic manner. Crystallite size refers to the average size of these individual crystallites within a polycrystalline material. Grain size, on the other hand, refers to the average size of individual grains within a polycrystalline material.

Both. First of all, we need to agree on the concepts.

These include: size, boundary, degree of perfection, scale.

Without them, we must apply the principle of indistinguishability.

Grains contain a group of crystallites oriented in different/single directions, further, each grain is separated from others with grain boundaries, with thick or thin boundaries. Crystallites generally come from the term polycrystalline samples, which contain crystal faces oriented in different directions.

"each grain is separated from the others by grain boundaries (GBs)": no GBs - no grain?

"from the term polycrystalline samples": grain boundaries are part of "crystallites". Is it possible to have no grain boundaries?

"a group of crystallites oriented in different/same direction": is it a single crystal or a texture?

Suggestion: scale of research tools: no magnification (macro) - no grains, homogeneous substance; optical microscopy (micro) - grain structure; electron microscopy (nano) - dislocations and other defects in the now crystal.

no grain-amorphous substance.

polycrystalline are quite different from single crystals.

optical microscopy shows grain boundaries on grinding and polishing.

electron microscopy deals with particle size and morphology.

Nanocrystals are not a "granular-amorphous substance"?

Grain Size is the Diameter of Grains of Atoms, This is Different from the Crystallite Size which Refers to the Size of a Single Crystal Inside a Particle or Grain.

nanocrystals are not amorphous compounds. They seem to have PXRD pattern slightly (the presence of a few broadened peaks) resembling, however, they are grouped into a category of polycrystalline substances.

In engineering materials, a crystal is usually referred to as a grain. A grain is merely a crystal without smooth faces because its growth was impeded by contact with another grain or a boundary surface. So, crystalline size is smaller than grain or particle size. Inside a grain or particle we have many crystals of identical orientation.

What is crystallity size? What it is meaning? To my mind such size should be biggest size for nonsherical crystallite. May be so. In this case we need to find largest possible size by means of microscopic technique. However, we,also, can average all the sizes over all area of crystallite and find the most probable suitable. But if we have a thin film we have numerous crystallites in our film. And what is the size of crystallites is the remnant question. By the following of the averaging way we should average all sizes of all crystallites and find average size by the using the procedure of averaging over all quantity of crystallites.

If we have grain of crystals which are in amorphous media we suppose that our crystal has the surrounding which consists of point defects, impurities, amorphous material and all of them (point defects, impurities) are concentrated around our purified crystal. Because, the grain of crystals doesn't have any defects and impurities. Only atoms of crystal's order.

Grain size is a diamter of individual grains of any particles.Where as, crystalline size is a size of single criyatall in single particle.

"A crystal grain has no defects or impurities. Only atoms of crystalline order."

Is it possible to imagine (not in theory!) a crystal without its own boundaries?

Let's say there are two points of view: (1) a fine crystalline powder and (2) a high viscosity liquid. Which is closer in mechanical properties to a polycrystal?

raman@

Grain Size is the Diameter of Grains of Atoms, This is Different from the Crystallite Size which Refers to the Size of a Single Crystal Inside a Particle or Grain.

Mehdi Noori Please explain 'Grain Size is the Diameter of Grains of Atoms'...

Crystallite size is always smaller than the Grain size.It is equivalent to single crystal.It may be just like single-domain structure.

While Grain size may contain one or more cystallites.It may be just like multi-domain structure.

Domain behavior, in case of magnetic material can be studied by variation of susceptibility with temperature.