Thank you Neetesh Soni , this helps a lot certainly,

Regards,

Dear Franklin , firstly I will explain about crystal

A crystal consists of matter that is formed from an ordered arrangement of atoms, molecules, or ions. The lattice that forms extends out in three-dimensions. Because there are repeated units, crystals have recognizable structures. Large crystals display flat regions (faces) and well-defined angles. Crystals with obvious flat faces are called euhedral crystals, while those lacking defined faces are called anhedral crystals. Crystals consisting of ordered arrays of atoms that aren't always periodic are called quasicrystals.

The word "crystal" comes from the Ancient Greek word krustallos, which means both "rock crystal" and "ice." The scientific study of crystals is called crystallography.

now grains and domain Usually domains are parts of a grain so that domains are ideally always smaller than grains, but...of course in case of special grainboundaries it might happen that domains appear bigger than a grain. However, I wonder what really happens then along the grainsboundary. The "connected" domain should show there lattice defects, i.e. a small grain boundary. 

I hope you you will get better idea . best wishes , also follow this article link its very effective to your discussion

Article Domains Beyond the Grain Boundary

Dear franklin. also see article link grain size and domain size distributions can be check by piezoelectric force microscopy in ferroelectric films with average grain size of 120-150nm. the domain size deviation decreases then the ratio of domain size to grain size increases, in a 1∕xn-type function, where n is 1.105.

"Correlation between grain size and domain size distributions in ferroelectric media for probe storage applications"

https://aip.scitation.org/doi/abs/10.1063/1.2363942?journalCode=apl

Dear Neetesh Soni:

Thank you for your definition of Crystals is very neat and complete, also understandable.

I also got your definitions about Grain and Domain. but I see that the limits between both concepts are thin, moreover, because as you said, depending of how grains are connected or separated, domains can be from different size.

I did get a much better idea, thanks

I'll see the attached articles,

Thank you, regards !

Dear Lipeng Xin :

What I wanted to know specifically was: What was the sequence order in lenght scale of the three concepts

With "domains" I meant in polycrystalline materials of any nature: dielectric, non dielectric, semiconductor, metals, diamagnetic, ...

Just considering in the definition the size/lenght scale of the objects.

Regards ! :)

Franklin:

In some cases, these terms may be used interchangeably. However, some distinctions may be made.

Grain when used for metals, minerals or homogeneous solid solutions is synonymous with crystal. For mixed phases such as a duplex metal it may refer to a type or size of structure. It may also refer to the size of a facet at a fracture surface. Of course, grain may also be used merely to indicate a separate particle size such as different grains of sand.

Domain is more difficult to define unless it is given more context. In ferromagnetic crystals, magnetic polarized domains may exist within the crystal. Domains may also refer to regions within a solid that have similar crystal structures, phases or properties.

So, it is not possible to give a specific order of sequence for length using these terms.

Dear Franklin,

À crystal is a single solid made of unique periodically arrangement of atoms that give well define form (cubic, hexagonal, etc.). Such forms are obtained by the formation of a nucleus that slowly grows without constrain. The size of a crystal can vary from mm to meters (see the crystals of Naica). By Pvd you can obtain beautiful crystals with a substrate heated near the melting point of the deposited metal.

A grain is a crystal whose growth has been constrained by others crystals growing in the neighborhood. The frontier between two grains "has" to accommodate the distortions of the two distinguished crystallographic arrangements. Thus the grain boundary is formed of many dislocations. Grain size varies from microns to millimeters. Their size can be determined by metallography.

When a metal is solidified, due to thermal or intrinsic stresses, the grains are elasticaly or plasticaly deformed. Inside a grain, little zones, called domains, are created that are homogeously deformed. Their size is thus smaller than the size of the grain. It can be determined by X Ray diffraction for example.

Hope it will be useful.

Dear Frédéric Durut :

Thsnk you for the reply, the three are good definitions, thank you for sharing information !

Kind Regards !

:)

@ Franklin Uriel Parás Hernández