5  Diffraction and Structure Factor

NoteLearning Objectives

• Derive the elastic diffraction condition in both its Bragg and Laue forms and connect it to reciprocal space.
• Explain how the Bravais lattice fixes where Bragg peaks may occur, while the basis fixes how strong they are.
• Define the atomic form factor and the cell structure factor, and relate them to measured diffraction intensities.
• Work out systematic extinctions for common structures and interpret them as reciprocal-space selection rules.
• Explain what a diffraction experiment measures in practice, including the role of the Ewald construction and the phase problem.
• Preview why inelastic scattering, rather than elastic diffraction alone, is needed to determine phonon dispersions.