X-ray diffraction

One of our condensed matter physics experiments

Goal: Determine the lattice constant and the crystal symmetry of several different solid state materials all of which have some type of cubic symmetry.

Simplest: "simple cube" atoms in the eight corners of a cube. Other more complicated possibilities:

• "Body center" 8 + 1 atoms (one more in the center)
• "Face centered" 8 + 6 (one more in the center of each face)

With x-ray diffraction can determine the separation between planes ("lattice constant") as well as the specific type of crystal symmetry

Interesting thing happens when you have a non-monatomic lattice

• eg: salt NaCl CsCl when the ions alternate in an interesting way

Take a powdered sample

• Detector,
• Count the number of scattered x-rays as a function of angle
• Brag law (which you will learn about during this experiment)

Requires some specific radiation safety training