Types of crystals, different methods of X ray diffraction and application of X-rays.

1. X-RAY CRYSTALLOGRAPHY
- Prepared by:
Chandni Pathak
En.no. - 2208212120001
M.Pharm (P’Chemistry) -
1st Sem
Parul Institute of
Pharmacy

2. Contents
● Types of crystals
● Different Methods of X-Ray Diffraction
● Application of X-Rays
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3. TYPES OF CRYSTALS
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4. Crystal Structure
● The crystal structure is an ordered array of atoms, ions
or molecules.
● A small group of a repeating pattern of the atomic
structure is known as the unit cell of the structure.
● The length, edges of principal axes and the angle between
the unit cells are called lattice constants or lattice
parameters.
● Crystals use x-rays, which excite signals from the atom.
The signals given by these atoms have different
strengths, and they usually depend upon the electron
density distribution in closed shells.
● The signals released by the atom varies.
● Lighter the atoms, weaker is their signals.
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5. Seven Crystal Systems
Sr. No. Types of crystals Sides Angles Shapes Examples
1. Triclinic System a ≠ b ≠ c 𝞪 ≠ 𝞫 ≠ 𝜸 ≠
900
Amazonite
2. Monoclinic
System
a ≠ b ≠ c 𝞪 = 𝜸 = 900
𝞫 = 1200
Kunzite
3. Orthorhombic
System
a ≠ b ≠ c 𝞪 = 𝞫 = 𝜸 =
900
BaSO4,
KNO3
4. Trigonal System a = b = c 𝞪 = 𝞫 = 𝜸 ≠
900
Calcite
(CaCO3),
Cinnabar
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6. Seven Crystal Systems
Sr. No. Types of
crystals
Sides Angles Shapes Examples
5. Hexagonal
System
a = b ≠ c 𝞪 = 𝞫 = 900
𝜸 = 1200
Mg, Zn, ZnO
6. Tetragonal
Systems
a = b ≠ c 𝞪 = 𝞫 = 𝜸 =
900
TiO2
7. Cubic System a = b = c 𝞪 = 𝞫 = 𝜸 =
900
NaCl, KCl
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7. Different X-ray
Methods
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8. X-ray Diffraction Methods
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9. A] Laue Photographic Method
- A small crystal is placed in the path of a narrow beam of
X-rays from a tungsten target at about 60 kV. The X-ray
beams used are of 0.2 to 2 angstrom (white X-rays).
- These X-ray beam will pass through a pinhole collimator
to get the sharp X-rays.
- These sharp beam of X-rays will go towards the sample to
be examined and it gives:
1)Transmission method
2)Back Reflection method
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10. 1) Transmission method
● Photographic plate is arranged on a rigid base and
diffracted radiation will strike the film and recorded
in the photographic film.
● It creates a specific pattern in the film known as
‘Laue pattern of spots’.
1) Back Reflection method
● It is used for large and thick specimen where
diffraction is difficult to get.
● Reflected radiation will create the Laue pattern in
photographic film.
● A big crystal is required.
● It is used to orient solid state experiment to
determine the single crystal symmetry.
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11. B] Rotating Crystal Method
- X-ray is generated in the X-ray tube and X-ray beam is
made monochromatic.
- Monochromatic radiation will fall onto the crystal
mounted on a shaft which can be rotated at uniform
angular rate.
- As the shaft rotates at a slow rate, it causes the set of
planes coming successively into their reflecting
positions.
- Whenever it follows Bragg’s equation, in that condition
reflection and diffraction occurs.
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12. 1) Complete Rotation Method
●Series of complete revolution takes place.
●Each plane in the crystal diffracts X-rays four times
during rotation.
●These four beams are distributed in the form of
rectangular pattern.
1) Oscillation Method
●Crystal is oscillated through an angle of 15-200
●The photographic plate is also moved accordingly.
●This method can be used to determine the size of the
unit cell in crystal.
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13. C] Powder Crystal or Debye Method
- In the place of large crystal, small amount of powder is
used as a sample in this method.
- X-ray is generated by X-tube tube and X-ray beam is made
monochromatic.
- Powdered sample is taken into a glass tube/capillary inside
the axis of the camera.
- The transmitted beam will be a passed through a hole to
minimize the fogging due to direct beam.
- On photographic film, diffraction and reflection pattern
will be recorded.
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14. - Different particles of the powder is having different
orientation of plane and they will show different pattern of
cone whose interaction with photographic film takes place.
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15. Applications of X-Ray
1] Structure of Crystals
➢ X-ray Diffraction method is non-destructive and gives
information on the molecular structure of the sample.
➢ The patterns obtained of unknown compounds are
characteristic of the particular compounds from which the
crystal was formed.
➢ Comparing diffraction patterns from crystal of unknown
composition with patterns from crystal of known compounds
permits the identification of unknown crystalline
compound.
➢ This method can also be distinguished between a mixture
of crystals.
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17. 2] Polymer Characterization
- Determines degree of crystallinity
- Non-crystalline portion scatters X-ray beam to give a
continuous background (Amorphous compounds)
- Crystalline portion causes diffraction lines that are not
continuous (crystalline materials).
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18. 3] State of anneal in metals
- Well-annealed metals are in well-ordered crystal form and
give sharp diffraction lines.
- If the metal is subjected to drilling, hammering or
bending, it becomes fatigued i.e. its crystals are
broken. Fatigue weakens the metal and can result in the
metal breaking.
- It is occasionally necessary to check moving parts for
metal fatigue, such as airplane wings. This check can be
done by x-ray diffraction without removing the part from
its position and without weakening it in the process of
testing.
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19. 4] Particle Size Determination
a) Spot Counting method
v = V 𝝳𝝷 cos𝝷/2n
v - Volume of individual crystal
V - Total volume irradiated
n - Number of spots in diffraction ring
𝝳𝝷 - Divergence of x-ray beam
This method is used for determining size of particles
larger than 5 microns.
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20. b) Broadening of Diffraction lines
Crystallites smaller than 120 nm create broadening of
diffraction peaks.
This peak broadening can be used to quantify the average
crystallite size of nanoparticles using the Scherrer’s equation.
c) Low-Angle Scattering
Both the above methods, give a mean crystalline dimension and do
not reveal anything about the distribution of particle size.
From Bragg’s relation, it follows that if one desires to have
information about large structural features, attention should be
focussed on small scattering angles, 2𝜭, to get better
resolution.
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21. Miscellaneous Applications
- Soil Classification based on Crystallinity
- Analysis of Industrial Dusts
- Study of Corrosion Products
- Examination of tooth enamel
- Examination of Bone State and Tissue State
- Structure of DNA and RNA
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22. References
1) Skoog, D.; Holler, J.; Crouch, S. Principles of
Instrumental Analysis. Thomson Brooks/Cole: CA, USA.
2007.
2) Crystal Structure. https://byjus.com/chemistry/crystal-
structure/ (accessed February 07, 2023)
3) Pradhan, K. Types of Crystals and Applications of X-Ray
Diffraction.
https://www.slideshare.net/KajalPradhan4/types-of-
crystals-application-of-x-ray (accessed February 07,
2023).
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