Materials Science and Engineering Crystalline and Non-Crystalline Systems X-Ray Diffraction: Determination of Crystal Structure.

Materials Science and EngineeringCrystalline and Non-Crystalline SystemsX-Ray Diffraction: Determination of Crystal Structure

Crystalline and Non-Crystalline

Single Crystals◦Uninterrupted repeating

unit of a unit cell◦Often forms geometric

shapes◦Most solids form multiple

crystal orientations and breaks forming grains

Crystalline and Non-CrystallinePolycrystalline

◦Many crystalline grains in a microstructure

◦Is heavily influenced by cooling. Nucleation, Growth, and Formation of

Boundaries (figure 3.18)

◦

Crystalline and Non-CrystallineAnisotropy

◦Axis/Direction determines properties (structure – properties correlation) Isotropy – Equal properties on all axis.

◦Example: Young’s Modulus, Conductivity, Index

of Refraction can vary between [100] and [111]

Crystalline and Non-CrystallineAnisotropy

◦Inversely proportional to structural symmetry Triclinic vs Simple Cubic

Highly anisotropic (directional dependant properties)

vs Highly Isotropic (uniform shape = uniform

properties)

◦Usually see isotropy on macroscopic scale in metals due to polycarystallinity

X-Ray DiffractionMost of the information in this

chapter comes from X-Ray Diffraction.

What is diffraction!?

X-Ray DiffractionDiffraction

◦Results from constructive and destructive interference

X-Ray DiffractionDiffraction

◦Consistent overlap in 3-D space creates “diffraction pattern”

◦Used heavily in research and higher education

X-Ray DiffractionDiffraction

◦Regularly spaced obstacles capable of scattering a wave

◦Are spaced comparable to wavelength

X-Ray DiffractionX-Rays

◦Form of electromagnetic radiation◦High Energy, Low Wavelength◦Portion of X-Ray beam scatters in

different directions (locations) when hitting solid object.

X-Ray DiffractionX-Rays

◦At an angle…

Bragg’s Law◦Relationship among x-ray

wavelength, interatomic spacing, and angle of diffraction for constructive interference

(further ahead)

X-Ray DiffractionLike Orchard Rows

◦Angle of view creates perspectives

X-Ray DiffractionTechnique:

◦Sample placed on a stationary rig◦Detector turns on rotating axis

Scans part along a set range of angles.

XRD Demo/Visual X-Ray Diffraction

X-Ray Diffraction◦Example:

X-Ray Diffraction◦What are we looking at?

X-Ray Diffraction◦What are we looking at?

X-Ray DiffractionWhat are we looking at?

◦What does each variable mean?