Crystalline Structures – Definitions and Calculations

Crystalline Structures – Definitions and Calculations

Materials are very important in engineering. To understand the materials in full aspects, we need to delve into the general atomic and molecular structures of atoms. So, we need to understand the crystalline structures to understand the behavior of such materials. Here, we explain the scientific and engineering background of crystal structures in detail. You can find every pinch of information about this topic here.

With the deep information that we give about crystalline materials and crystalline structures here, you will be able to interpret lots of kinds of engineering facts behind these materials. So, it will be a very good starting point for the crystals and crystalline structures for you.

Also, you will find very deep information here about the imperfections and defects of crystalline structures.

What is Crystalline Structure?

Types of crystalline structures.
Image Source: EnggStudy.com

Crystalline materials have a very regular atomic arrangement between atoms. This arrangement is there is a linear regularity between the atoms and molecules all over the solid. Because of this very regular arrangement of the solid structures, we call these structures crystalline structures. Also, we call these systems crystals which are very specific types of crystalline structures.

Crystals are the packing of atoms and ions in an ordinary regular way to obtain a very regular solid. Most of the ceramics are crystal structures.

We use the general term lattice to describe the general packing of atoms. Lattices are the minimum size of expression of the crystalline structures. If you unite lots of lattices, you will obtain the general crystal structure of that material.

Also, we are using unit cells to describe the general structures of crystalline structures. They include the atoms and molecules of a crystal structure in a parallelepiped unit cell that gives a general idea of how a crystalline structure takes place upon solidification. We are making lots of kinds of classifications and descriptions of crystalline structures by using unit cell structures.

Crystalline structures are very common in engineering materials. We use them in different kinds of applications and systems.

Crystalline Structures on Metals

The atomic arrangements in metals are very important to us. We understand the general behaviors and characteristics of metallic atoms and metals by understanding the structures. Also, metal atoms have crystalline structures between each other. So, they have crystalline properties and features that we need to delve into. First of all, we need to state that, there are three main types of crystalline structure types of most metals;

  • Face-Centered Cubic Structures(FCC)
  • Hexagonal Close Packed Structures(HCP)
  • Body-Centered Cubic Structures(BCC)

Let’s check the general crystalline structures of metals that have. They have a very big influence on physical properties.

Face-Centered Cubic Crystalline Structures

If we take a look at the general structure of the unit cells of FCC metals, the atoms are located on the edges and the face centers of the cube structure of the unit cell. If we take a closer look at the FCC crystalline structure we will see that each atom at the edges is shared between 8 FCC unit cells. And each atom at the face is shared between 2 unit cells. If we think that the cube has 6 faces, we can assign 3 atoms to one unit cell. And we can assign only 1 atom at the edges to 1 unit cell. So, each FCC unit cell is responsible for 4 atoms.

  • Edge length calculation for FCC structures;
Edge length calculation of crystal structures.

In this equation, R is the total length of the atomic radius in that metal. The unit of the length and the radius is nanometers.

  • Atomic packing factor calculations;
Atomic packing factor formula of crystalline structures.

We calculate this value for each kind of unit cell in general. The atomic packing factor represents how much volume of an atom is packed inside a unit cell. So, it is a very important parameter to define the general characteristics of metals. For most of the FCC crystalline structures, the atomic packing factor value is 0.74.

Body-Centered Cubic Crystalline Structures

In the BCC structures of metals, there is one atom at the center of the cube and there are 8 atoms at the edges of the unit cells. We calculate the atomic length of the body-centered cubic structures as;

Atomic length of body centered cubic structures.

The atomic packing factor of BCC crystalline structures is less than the FCC structures. Their APF of them is 0.68.

Hexagonal Close Packed Structures

The structure of the HCP crystalline structures in metals is somewhat different from the other ones. The crystalline shape is a hexagonal prism. And at each corner of this hexagonal prism have one atom. And also, at the center of the top and bottom surfaces of the hexagon prisms, there is one atom. So, at each hexagon surface, there are 7 atoms. And also, there is a triangular 3 atoms in the middle between these two surfaces. So, to obtain a complete HCP structure, we need 17 total atoms.

Also, different types of unit cell structures can cause the phenomenon of allotropy or polymorphism. In these systems, the chemical compounds of the metals can be completely the same. But the physical properties and appearances can differ.

The most important example of it is iron. Pure iron has a BCC structure in general. But it changes after a temperature to FCC structure which has a completely different structure from its pure form.

Also, pure carbon can transform into a diamond at extremely high pressures. This is also a very important example of polymorphism or allotropy.

So, these 3 types are the general crystal structures in metals.

Crystalline Structures of Most Common 16 Metals

MetalsAtomic Radius in NanometersCrystal Structure
Aluminum0.1431FCC
Cadmium0.1490HCP
Chromium0.1249BCC
Cobalt0.1253HCP
Copper0.1278FCC
Gold0.1442FCC
Iron0.1241BCC
Lead0.1750FCC
Molybdenum0.1363BCC
Nickel0.1246FCC
Platinum0.1387FCC
Silver0.1387FCC
Tantalum0.1387BCC
Titanium0.1387HCP
Tungsten0.1387BCC
Zinc0.1332HCP
The general crystalline structures and atomic radii of common metals.

As you see above, there is no correlation between the diameter of atoms and the structures. Different metals can have different kinds of structures.

Close Packed Crystalline Structures

As you see above, the HCP and FCC crystalline structures have the same amount of atomic packing factors. Also, they have very different orientations in planes. Because the planes of atoms are structured differently in HCP and FCC systems. For example in HCP structures, the hexagonal and triangular planes of atoms stick to each other to form the HCP structures.

Also, the triangular big planes of atoms are stacked to each other to form the FCC structures.

In other words, the densities of the close-packed systems are higher in general. Because much more atoms fit inside a specific area in the closed-packed system.

Theoric Density Calculations of Crystalline Structures of Metals

Also, we can make theoric density calculations of metals by knowing their general crystalline structures of them. So, it will be very easy for us to calculate the density. We can use this theoric density with the real density of metals to compare how much they are closer to the theoric structures. We can use this calculation here;

Density formula of crystal structures.

In these equations, the variables are very simple.

  • n is the total number of atoms in a unit cell.
  • A is the total atomic weight of metal.
  • V is the total volume of the unit cell.
  • AN is the Avogadro’s Number which equals 6.023 x 10^23 atoms/mol

As you see above, with the increasing number of atoms in a unit cell, the total density of metal increases. So, there is a strict relationship between the type of unit cell and the density of metals. For example, the density of gold is very high around the metals. And this element has FCC structure which is a very packed structure that has the biggest atomic packing factor among others.

Also, atomic weight is a very important factor that affects density positively.

You can make comparisons between the theoric density and the actual density of the metal to see the closeness to the theoric value. In general, we expect these theoric values from pure metals.

Crystalline Systems and Shapes in Theoric Applications

Also in theoric applications and studies, we generally use crystalline systems and lattice parameters. Lattice parameters explain lots of kind of things about crystalline systems and different crystal systems.

In lattice parameters, there are 6 important parameters which are axial relationships and interaxial angles. Actual relationships are about the lengths of the sides of the cube structure. And interaxial angles are about the angular relationships between these sides.

a, b, c are the lengths of the sides,

α, β and γ are the angles between the sides.

According to the different kinds of relationships, there are these types of crystalline systems: cubic, hexagonal, tetragonal, rhombohedral(trigonal), orthorhombic, monoclinic, and triclinic types.

We use these general crystal systems to explain different kinds of mechanical and physical properties of materials. But do not forget that, these are the theoric assumptions. The property predictions according to these theories can vary with the real properties of materials.

Cubic Crystal Systems

In the cubic crystal systems, all the sides are equal to each other. And all the angular relationships are 90°. So, the unit cells of these structures are complete cubes. They are the most regular systems among the other ones.

Hexagonal Crystal Systems

Hexagonal crystal systems are the systems that are not in the shape of a parallelepiped. But we also describe it by the 6 lattice parameters again.

If we divide the hexagonal crystal systems into 3 equal parallelepiped prisms, we can make our evaluations. So, the axial relationships are all same and a = b = c. And also if we look at the angular lattice parameters, the two are α = β = 90° and γ =120°.

And if we combine the three of them, we can obtain a hexagonal crystal system. Hexagonal systems are different from the other kinds of systems. Because other systems have rectangular shapes.

Tetragonal Crystal Systems

In these systems, the only difference is that one of the sides is not equal to the other ones. And all the angular relationships are the same as the cubic ones. So, the only difference between it from cubic crystal systems is a = b ≠ c. So, there is a slight difference between the tetragonal crystals and the cubic crystals.

Rhombohedral or Trigonal Crystal Systems

In the rhombohedral systems, all the sides are equal to each other. And the angles between each side are not equal to 90 degrees but equal to each other. So;

a = b = c

α = β = γ ≠ 90°

The skewness of the prisms starts with the rhombohedral systems.

Orthorhombic Systems

In these systems, all the sides of the unit cell are not equal to each other. But all the angular relationships are equal to each other and 90 degrees. So;

a ≠ b ≠ c

α = β = γ = 90°

They are also very regular systems but their edges are not of the same length.

Monoclinic Crystal Systems

Also in monoclinic systems, sides are not equal to each other. And only one angular relationship is not equal to 90 degrees. So;

a ≠ b ≠ c

α = γ = 90° ≠ β

Triclinic Crystal Systems

They are the most skewed unit cell systems. In triclinic systems, all the sides are different in length from each other, and all the angular relationships are different and not equal to 90 degrees. So;

a ≠ b ≠ c

α ≠ β ≠ γ ≠ 90°

So, these are the general explanations of the types of crystal structures in metals.

Types of Crystalline Materials

Crystalline materials and crystalline structures are very important for us in different kinds of applications. There are two major classes of crystalline structure; single crystals and polycrystals.

Single-Crystalline Structures

Single crystalline and poly crystalline structures.
Single crystalline and polycrystalline structures(Image Source: Researchgate.com).

If we take a look at the structures of single crystalline structures, we can see that the same crystal structure is dominant in the general structure of the material. So, there is the same unit cell orientation in the single crystal materials.

In nature, we can find single crystal materials. But obtaining them requires very distinct external features. So, the production of single crystals is also very common artificially.

We use these types of crystals in technology and electronics. For example, we use single crystal silicon-based materials to obtain the semiconductors of electronic circuits.

Single crystalline structures are not common in application. Most of the time, we require polycrystalline structures.

Polycrystalline Structures

Also, there are polycrystalline structures in nature and artificial production. The difference between these structures, they have particular grains composed of crystalline structures. And there are grain boundaries between these grains.

In the solidification phases of polycrystalline structures, grains begin to form as crystal structures by taking the adjacent atoms in the liquid. Once these grains begin to be big enough, grain boundaries form between them. So, the occurrence of polycrystalline structures is simple like this.

Polycrystalline structures are the most common types of crystalline materials. We need grain boundaries in these systems.

Isothrophy in Materials

Isotropy is a very important feature in materials. Isotrpohy means the general properties of a material along a line or surface. If these properties are not changing or minimal changes, we call these materials isotropic materials.

Also, if there are changes in these directions, we call these materials anisotropic.

Isotropy is a very ideal thing that takes place in theoretical calculations. In real applications, there are no properties that have perfect isotropy. Most of the materials are anisotropic. But in engineering calculations, we assume them as isotropic materials.

And also, we desire the materials need to be isotropic. Because we are sure about all the properties same in each direction and our assumğtions and calculations are much more accurate.

The closest materials to isotropy are single crystal materials. Because they have a very high level of order between the atoms. And there is nearly no change in the structure of the material.

The level of isotropy changes according to the molecular structures of materials and impurities. So, there are lots of kinds of parameters that define the isotropy in materials.

Common Crystalline Materials

As we stated above, there are lots of materials that have crystalline structures. So these structures are very important. We use these materials in lots of kinds of engineering applications. You can find the most common crystalline materials and their applications of them.

Crystals.
Image Source: Wikipedia.com.

Metals

Most of the metals have a crystalline structure. Maybe we can think of them as the posses non-crystalline behaviors such as malleability or low electrical resistivities. These low electrical resistivities come from their valence electron structures. The atoms of metals are free to move over the atoms. So, there is an electron sea that produces very ductile and very low electrical resistance. But in essence, they are crystalline materials.

We use metals commonly in different kinds of technologies and engineering applications. Around these applications, you can say; automotive, aerospace, and other kinds of things. Also, there are different kinds of production techniques that we use metals. One of the most important applications is sand casting operations. In these operations, we generally cast the molten material inside the molds. And we obtain the solid structures.

So, solidification takes place in these metal casting operations. And grain boundaries form between the crystalline grains.

It may seem that the information about metals is crystalline. Because people generally know the metals as ductile and malleable ones. But they have a very crystalline atomic arrangement.

Ceramics

If we compare them with metals, they are not ductile and completely brittle materials. Because there is no electron sea phenomenon for the ceramics. And also, they are not good at transferring electricity on them.

Also, the most common ceramics are crystalline materials. So, the general structures of these ceramics are crystalline structures. It is very important to consider this phenomenon.

Their excellent brittle nature comes from the ionic bonds. Between the atoms, there are ionic bonds to obtain these ceramic structures. So, these ionic bonds create crystalline structures on a bigger scale. And grain formation is also very common in the structures of ceramics. It is a very important aspect that we need to consider.

We use different kinds of ceramic materials in different engineering applications. For example, in refractory applications, the use of ceramics is very common. Because they are very resistant to high temperatures. Their melting points are very high because of the strong ionic bonds between the atoms.

Furthermore, we use molding applications to produce ceramic shapes and parts. We prepare slurries and cast these slurries inside the molds to obtain the ceramics parts. While the solidification of these slurries, the grains and grain boundaries form.

Also, some ceramic materials do not have crystal structures. We can find amorphous ceramic materials in nature.

Importance of Grain Boundaries in Engineering Applications

Grain boundaries in crystalline structures.
Grain boundaries.

By using the crystalline structures and grains of these structures, we obtain very different properties from materials. The grain boundary phenomenon is very important as imperfections in solids. They are forming obstacles to the possible cracks in solids.

Increasing the Mechanical Strength

Grain boundaries are the natural obstacles to possible crack formations in the structures of solids. For example, a crack may form in a grain boundary. So, this crack formation can bump into a grain boundary and then stops. So materials with higher grain boundaries, are strong mechanically.

Also, there are heat treatment applications to obtain finer grains and smaller grains in the crystal structures of materials. By applying these treatments, they increase the total mechanical strength and toughness of materials.

Understanding the nature of grain boundaries in materials, especially in metals, equals understanding lots of physical characteristics in certain situations. In this article we will explain the grain boundary structures in crystalline materials and how can we interpret the materials’ situations according to these microstructures.

Grain Boundary Formation

Grain boundaries occur in the cooling phase of crystalline material. Each grain’s boundaries have its crystal orientation. Because of these different orientations, boundaries occur between these differently oriented crystal microstructures. Also in grain boundary regions, there can be a few amounts of atoms that do not belong to either of the crystal orientations in the material. The number of grain boundaries in a material depends on the number of nucleation zones that exist. Each nucleation zone in the solidification of the material creates a crystal grain. So the number of nucleation zones can be increased artificially to obtain much more grains and grain boundaries in material.

Generally, these artificial nucleation zones are created by cold walls inside the mold.

To obtain much more bigger grain size which also means lower grain boundaries are obtained with a faster cooling rate. Also, the reverse situation can be achieved with a slower cooling rate.

The smaller grain sizes are preferable in materials engineering. Smaller grain sizes mean much more grain boundaries in material. When there is a stress application on material, grain boundaries prevent the emergence of imperfections in the microstructure, which means much harder than bigger grained ones.

Also, smaller grain bounded materials have very good forming capabilities, because these materials are much more ductile compared with bigger grained ones. Better surface qualities can be obtained with smaller-grained materials.

In the solidification process, the sub-process called strain hardening is applied to obtain smaller grain sizes in crystalline materials.

Directional Solidification Applications

Also, we expect different kinds of properties and directional strength from materials and parts. So, to obtain them, the direction of the grain boundaries in crystalline structures is very important.

With the special solidification techniques, we obtain directional grain boundaries which make the material stronger to the crack formations in that direction. So, these solidification techniques are very advanced and used for specific applications.

Also, perfect crystalline structures can be very desirable in engineering applications. For example, the price of a diamond depends on the perfectness of the crystalline structure of this diamond. Also, defects can occur in crystalline structures such as grain boundaries. Crystalline structures occur inside grain boundaries inside a material. The density of these grain boundaries means much more defects in the crystalline structure.

Also, directional solidification to obtain the grain boundaries in specific directions is a composite material application.

Adjusting Translucency

With the density of the total grain boundaries in the crystalline structure of the material, we adjust the translucency. Fully transparent systems are single crystaş structures or non-crystalline structures in general. With the grain boundaries and the imperfections on solids, we obtain translucent objects.

Also, we can adjust the level of translucency by adjusting the density of grain boundaries. So, different kinds of materials that we can obtain different transparencies.

So, these applications are very common in optical systems. Translucency is not only dependent on the grain boundaries. Also, other factors are important such as imğurities and defects.

Non-Crystalline Materials

Crystalline and amorphous.
Crystalline and amorphous.

Also, non-crystalline materials are very common in nature. If we give a summary of these materials, it will be very easy for the readers to make comparisons between these two classes.

As you understand from its name, non-crystalline materials are materials that do not have any crystalline structures. So, all the atoms and molecules are connected irregularly. Also, we call these materials amorphous materials.

We can obtain the amorphous structures from the crystalline structures over the solidification. If the solidification of material is rapid enough, we can obtain certain degrees of non-crystalline structures inside them. So, we adjust the level of crystallinities in the solidification phase.

Examples of Non-Crystalline Materials

Also, non-crystalline structures are very common in nature. Around these non-crystalline structures, glass, some ceramics, and polymers.

  • Non-crystalline Ceramics: Some ceramics have non-crystalline structures in nature. Upon solidification, they are not forming any crystalline structure. So, the atoms and molecules of these ceramics are randomly oriented.
  • Glass: Glass materials are also very important examples of amorphous materials. You know that they are completely transparent. Because there are no grains or grain boundaries that come with a crystalline structure.
  • Polymers: Most of the polymers have non-crystalline structures. The links and chemical bonds are very complex. So the formation of crystalline structures in polymer materials is hard. But, some polymer materials have some degree of crystallization. So, their application is very common.

Melting and Solidification Characteristics of Non-Crystalline Structures

Also melting and solidification nature of the amorphous materials are very different from the crystalline structures. They do not have a distinct melting temperature. There is a transition between the solid and liquid phases. We call this transition phase temperature as glass transition temperature(Tg) where the solid characteristics become liquid characteristics or vice versa.

Also, In crystalline materials, phase change between the solid and liquid state is abrupt. There is a specific temperature for this phase transition for crystalline materials. Molecules or atoms transfer abruptly from regular-packed solid arrangement to irregular unpacked liquid arrangement or vice versa at melting temperature.

In the production technology, we use this glass transition temperature value in the applications. Because it provides a very high degree of shapeability of these materials. We can shape the amorphous material in the transition phase and solidification it.

For example, glass liquefies slowly, in the starting of liquification, the viscosity is very high. This transition state of glass or amorphous materials is called a ‘supercooled state’. After a certain time of heat transfer to the glass, there will be a phase change to the fully liquid state. The temperature that this change occurs is called ‘glass transition temperature’ for amorphous materials.

We use this kind of melting or solidification in different kinds of shaping applications also.

Types and Effects of Different Imperfections

Imperfections and defects are also very important in the general structures of crystals. There are lots of kinds of applications that we use these imperfection and defect mechanisms. Here we explain the general defect mechanisms and effects of crystalline materials.

In theoric calculations and assumptions that we made for crystalline structures, we are not considering any kinds of impurities and defects that make deviations from these structures. So, it is very important to consider the imperfections and defects.

We call these unintended or sometimes intended differences from theoric assumptions imperfections and point defects.

Types of Point Defects on Crystalline Structures

Point defects are the defects that take place in a point. In the atomic and molecular structure, point defects are very common. And considerations of them also have a very big impact on both the mechanical and physical features. Also, there is a strict correlation between the point defects and the entropy law of thermodynamics. Because the entropy or randomness increases with the point defects.

There are generally two types of point defects in the crystalline structures of materials;

  • Vacancies
  • Interstitials
Vacancies and self-interstitials.
Vacancies and self-interstitials(Image Source: Researchgate.com).

Vacancies

The first important point defect is vacancies in the crystalline structures. They take place with a missing molecule or atom in the regular structure of the crystals. Also, they are very common defects that can take place.

We can not create a crystalline structure without vacancies. Because we can not control all the atomic places that crystalline structures have.

With the increasing vacancies, the randomness of the crystal structure increases.

Self-Interstitials

Also, self-interstitials are the most common point defects. Self-interstitials form when the extra atoms are placed between the regular structure of crystals. It is the negative version of vacancies of atomic structures.

In general, the total concentrations of self-interstitials are least common if we compare them with the vacancies. Also, they lead to distortions in the regular structure of the crystals.

Impurities in Crystalline Structures

In general, we can not obtain a completely pure material or metal. Always, there are impurity atoms or molecules in their structures of them. Even with the most advanced production and purification techniques, the total percentage of purity is 99.9999%. So, there are 0.0001% of impurity atoms in the crystalline structures.

In most engineering applications, we use impurities to obtain more strong materials or more durable systems. We do not need to see the impurities in materials as a negative thing. Because pure materials are not generally useful in general practical applications.

Substitutional and Interstitial Impurities on Crystalline Structures

We stated the general working principles of substitution and interstitial defects or purities above. So, if another type of atom comes and takes the place of the normal atoms in a crystalline structure, this is the substitutional impurity. But also, if another atom is placed between the little places of crystalline atoms, it is the interstitial impurities.

In the impurity solutions, atomic size is very important. If the difference between the atoms to be mixed as impurity is less than 15%, the substation impurities and solutions take place. Otherwise, interstitials may form and another kind of phase can take place.

Also, these types of impurities and defects take place only in crystalline structures. So, it is very important to have a crystalline structure to obtain these kinds of structures. It is not possible or little possible in non-crystalline structures.

Furthermore, if the electronegativity of an atom group and electropositivity of another atom group is high, the total possibility to form these kinds of compounds is easier.

Metal Alloys

Metal alloys are the practical applications of adding impurities to obtain better mechanical and physical structures. For example, pure iron is very ductile and has low mechanical strength. But with the addition of impurities such as carbon makes them very high-strength materials such as steel or cast iron. Carbon takes the place of iron atoms and makes the structure more durable. This is a very common practice of alloying. And the carbon forms interstitial solid solutions in the iron element.

There are lots of kinds of different alloying techniques and types. And these alloying techniques are separate examples of impurities.

Also, the alloying elements will be solved inside the alloyed metal. For example, carbon is soluble inside iron. So, we obtain solid solutions by alloying the metals and elements between each other. We call iron a solvent, and solute is carbon. Impurities take place at the atomic level with this mechanism.

Furthermore, the total number of valence electrons has a very big influence on the formation of alloys. If the hosting metal has higher valences, the formation of solutions and alloys is higher likelihoods.

In other words, most metal alloys take place substitutions of atoms inside each other. So, the solution takes place like this.

Effect of Atomic Packing Factor

For interstitial solid solutions, the atomic packing factor has also a very big effect. We need to consider this effect. Because, if the packing factor is high for metal, the formation of interstitials is very hard. So, there is no place for new atoms inside the crystalline structure.

So, you can see the effect of the atomic packing factor that we defined above.

Composition Calculations of Solid Solutions and Alloys

We can use direct mathematics to calculate the compositions of alloys and solid solutions. Because there is no loss of any mass or atoms and energy in the formation of these mechanisms.

For example, if you want to calculate the weight percent of an alloy or solid solution of crystalline structures, just use this relation;

Weight calculations.

As you see here, m1 is the total weight of the first composition that you want to calculate the weight of it. And the m2 is the second material that you need to use to calculate the weight percent.

And also, you can calculate it with the atom percent of it. You just need to use the moles and Avogadro’s number to calculate it. The equation is the same as above.

Dislocation Defects on Crystalline Structures

Dislocations in crystal materials.
Dislocations.

Dislocations are also very important types of defects in crystalline structures. In general, these defects are not related to the atoms or molecules of a structure. They are generally placed as replacements. for groups of atoms and molecules.

Edge Dislocations

In these types of dislocations in crystalline structures, an extra half plane in the crystal structure. So, very high distortion takes place between the section that has a half-plane and that does not have that half-plane.

The edge of the half-plane of atoms is the line of dislocation where the distortion occurs. With the increasing distance from the edge dislocation line, the level of dislocations gets lower.

Screw Dislocations

In this type of dislocation, a one-row shift of atom groups take place in the crystalline structures. So because of this slip, a volumetric dislocation takes place. Because of this volumetric dislocation, the slip takes place.

These types of dislocations can take place because of the action of shear forces on the material. Because these shear forces apply shear stress to obtain screw dislocations.

Mixed Dislocations

We can also observe mixed dislocations in the crystalline structures. Also, all the dislocations are mixed dislocations which are a combination of screw dislocations and edge dislocations.

We use these dislocation mechanisms to benefit from them.

Think about a material that does not have any dislocations. So, we can apply force to deform it. They have a very big deformation capacity. But after a level, the deformation stops, and fractures take place.

By increasing the dislocations in the ductile crystalline structures, we can obtain more tough and higher structural integrities. We call these processes strain-hardening processes.

Grain Boundaries

We talked about the grain boundaries above. Grain boundaries are the natural outcomes of the solidification of crystalline structures. They are the boundaries between the crystals. So, we can consider them as defects in the structures.

Grain boundaries are very important to us. Because we use them to the advantage of the different applications. One of these applications of grain refinement is to obtain more tough and mechanically strong systems.

Bulk Deformations and Volume Defects

Also in engineering, bulk deformations are very common. They are the types of deformations that you can observe with your naked eye. For example, the deformations inside the structure of a material such as cast iron. Casting defects can be a very big problem as bulk deformation.

Internal voids are also very big structural problems. They can lead to strength problems of structures. For instance, the internal void in a shaft can cause failures or cracks.

Surface Defects

The surface of the crystalline materials is also very important. Because surfaces are the termination point of the crystalline structures. The atoms and molecules at the surface do not bond with other atoms. Because of it, the general situation of the surface is very important in defects.

There can be bulk surface defects on crystalline materials. The general cause of these surface defects can be external factors such as production techniques.

These bulk defects can be a problematic issue in the mechanical strength of the materials. They can be starting points of cracks or other failure reasons. So, we generally give special attention to the surface characteristics of materials that we produce in general.

As you understand, we generally deal with both little deformations and defects and bigger bulk ones to obtain more reliable and strong materials.

Conclusion on Crystalline Structures

As you see above, crystalline structures are very important in engineering and practical applications. You need to know the general science behind these structures.

Also, crystal structures are very important for metals. To understand the general characteristics of metals, you need to understand their crystalline structures of them.

And also, we make theoric calculations on the crystalline structures. Because it is very important to know the theoric values of different physical features such as density and mechanical strength.

In general, we have two types of crystalline structures which are polycrystalline and single crystals. We use polycrystalline structures in engineering applications.

Around the common crystal structures, metals and ceramics have a very important place. So, to understand the general principles and physical properties, we need to understand the structures of these materials.

In crystalline structures, understanding the general mechanisms of impurities and defects is also very important. We obtain different kinds of structures by using impurities and defects in these materials and structures.

Furthermore, if you understand the general logic of the grain boundaries, you will be able to assess most of the different things about their properties.

Finally, do not forget to leave your comments and questions below about this topic.

Your precious feedbacks are very important to us.

FAQs About Crystalline Structures

What is meant by crystalline structure?

This term defines the general molecular arrangement which they are in a very regular system. The orientations and the orders of atoms are very perfect. To define these structures, we use this term.

What are the examples of crystalline structures? 

The most important examples are metals and ceramics. Most of the metals have crystal structures. And also general ceramics have crystalline structures. But some of the ceramics are amorphous in structure and there is a random order between the atoms and molecules.

What are the 7 crystal structures?

Among the 7 crystal structures; are triclinic, monoclinic, orthorhombic, tetragonal, trigonal, hexagonal, and cubic. These structures are theoric assumptions about the shapes.

What are the three types of crystal structures?

The metals have three types of crystal structures. These three types are, hexagonal packed structures, face-centered cubic structures, and body-centered cubic structures.

What is a simple crystal structure?

In simple crystal structures, the places of atoms are at the corners of the cube. This structure is so simple if we compare it with the other body-centered cubic, face-centered cubic, and hexagonal close-packed structures.

What are the characteristics of crystalline structures? 

The most important characteristics of these structures are; that they have a very regular atomic arrangement. Also, they possess grain boundaries which are very important in the development of high-strength materials. They possess certain melting and boiling temperatures, unlike amorphous materials.

How many crystal types are there?

In nature, there are 7 main types of crystal structures. These structures are triclinic, monoclinic, orthorhombic, tetragonal, trigonal, hexagonal, and cubic. These structures have different shapes. So, materials that have these different shapes in their structures, have different properties.

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