Practical Aspects of X-Ray Diffraction

Abstract

In this and the following sections we provide some general experimental background to the x-ray diffraction technique. Each manufacturer’s instrument has its unique features, and for specific details you should refer to the instrument operating manual that came with your diffractometer. The experimental geometry used in the powder diffraction method is illustrated in Fig. 42. The three basic components of an x-ray diffractometer are the

• • X ray source

• • Specimen

• • X ray detector

and they all lie on the circumference of a circle, which is known as the focusing circle. The angle between the plane of the specimen and the x-ray source is θ, the Bragg angle. The angle between the projection of the x-ray source and the detector is 2θ. For this reason the x-ray diffraction patterns produced with this geometry are often known as θ-2θ (theta-two theta) scans. In the θ-2θ geometry the x-ray source is fixed, and the detector moves through a range of angles. The radius of the focusing circle is not constant but increases as the angle 2θ decreases, as you can see from Fig. 42. The 2θ measurement range is typically from 0° to about 170°. In an experiment you need not necessarily scan the whole range of detector angles. A 2θ range from 30° to 140° is an example of a typical scan.