Measurement of accurate Bragg intensities

Abstract

Abstract The accuracy of atomic parameters obtained by X-ray crystal structure analysis depends on many factors: the measuring procedure and the treatment of the measured intensities, the scattering power of the crystal at high Bragg angles, the methods used to refine the atomic parameters, and others. This chapter will deal mainly with the problems of measuring accurate integrated intensities on a standard four-circle diffractometer and of correcting these intensities for various factors to derive the kinematic Bragg intensities. The collection of a complete set of accurate X-ray intensities to high resolution with a standard diffractometer is very time consuming, even for small unit cells. For example for the structure analysis of Li BeF at 81 K (Seiler and Dunitz 1986) more than 40 000 X-ray intensities were measured over a period of about three months.