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Determination Of Crystal Structure - Coggle Diagram
Determination Of Crystal Structure
X-Ray
energy, E=hv= hc/λ
X-ray diffraction
can identify crystalline phases and orientation
to determine structure properties
to determine atomic arrangement
reciprocal lattice
represent Fourier transform of another lattice
used to determine whether the plane satisfy Bragg' law
vector
powder technique
single or polycrystal are grounded into powder form
orientationof the powder are randomly oriented
the sample powder the is placed into a container at placed in line of monochromatic X-ray
let say that a crystal is orieted such that an X-ray beam is diffracted with high iintensity occur at diffraction angle
If the crystal is rotated around an axis same as the incident beam, diffracted rays form a cone with its peak on the crystal and its cone angle is twice the diffraction angle
The incident monochromatic radiation strikes a finely powdered specimen n a thin walled capillary tube
convenient because single crystal are not required
Diffracted rays go out from individual crystallites which happened to be oriented with planes making an incident angle θ with the beam satisfying the Bragg equation
neutron
use to study magnetic structure of material
electron
suitable for surface study of crystal, thin film and thin crsytal
Laue technique
kincident ray comprises of various λ
sample is single crystal
Transmission tachnique
Film use for recording
the diffraction pattern is placed behind the
sample and records the forward diffracted ray
reflected ray technique
film use for recording the diffraction pattern is placed between source & sample
how diffraction work
beam scattedred unifromly in all direction
scattered beam will intefere constructively in some direction
random arrangement cause beam to randomly interfere and no distinctive pattern is produced
Bragg's Law
d-spacing
cubic
tetragonal
orthorhombic
hexagonal
monoclinic
it explain the diffracted rays from crystals
Ewald Construction
Bragg and Laue Diffraction
both deal with elastic scattering of periodic lattice
bragg consider lattice object that are grouped in families of plane & the incident radiation is specularly reflected
Laue doesnt require assumption of particular plane & spacing & reflection to be specular
Laue equation
ewald sphere of diffraction
describe as in reciprocal space by Ewlad Sphere construction with r= 1λ
each reciprocal lattice is located on the sphere of reflection satisfy Bragg condition
geometric construct used in electron, neutron and X-ray crystallography
Bragg reflected ray
Bragg rule for specular reflection
refelction is elastic
By changing λ so the reciprocal lattice either shrink or expand
lattice points touching the sphere surface and Bragg’s or Laue requirements are fulfilled
Laue technique
fixing λ but moving & turning the reciprocal lattice points
Powder technique
