L18 - SUMMARY FROM LAST CLASS X-ray diffraction: Each...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Dr. P. Lucas U of A MSE 110 X-ray diffraction: SUMMARY FROM LAST CLASS Each crystal structure has a specific set of planes and d-spacings and can be defined by this unique collection of d-spacings. XRD is used to determine crystal structures by measuring d-spacings. X-rays are energetic photons generated by atomic core electronic transitions made possible by the creation of an electron vacancy on the K level (n=1). Electron vacancies are created in X-ray tubes by knocking off K electrons with a high energy electron beam. The beam of X-rays is reflected by subsequent atomic layers in the crystalline sample if the path length difference between rays reflected by subsequent atomic layers is equal to a whole number of wavelength. All the rays are then in phase and interfere constructively. The conditions for refraction are expressed in Bragg’s law n λ =2d·sin θ The incident beam angle θ is scanned between 0 and 90º and a peak is recorded for the d-spacing of each atomic plane.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Dr. P. Lucas U of A MSE 110 Bragg’s Law: reflection order n XRD he reflection order n is equal to the number of wavelength in the path difference owever the size of λ is typically of the order of d (hence n<2) so that we usual tion n=1 and Bragg’s Law reduces to: Ray 1 Ray 2 Ray 3 n λ =2d·sin θ rom Bragg’s law therefore n λ <2d 1 sin 2 < = θ λ d n λ = 2d·sin θ T between two rays reflected from subsequent atomic layers. H ly only consider the first order reflec F
Background image of page 2
Dr. P. Lucas U of A MSE 110 X-Ray pattern: We can then calculate the set of d corresponding to the crystal structure. XRD
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 14

L18 - SUMMARY FROM LAST CLASS X-ray diffraction: Each...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online