On the temperature factors of X -ray reflexion for sodium and chlorine in the rock-salt crystal

Abstract

1. The influence of temperature on the intensity of reflexion of X-rays by crystals was first dealt with theoretically by Debye, and later by Waller, each of whom based their work on the dynamical theory of crystal lattices due to Born and Kármán. Measurements of the temperature coefficient for rocksalt at high temperatures have been made by James,! and at the temperature of liquid air by James and Miss Firth. In their paper, the latter compare the observed intensities, both at high and low temperatures, with those predicted by Waller’s theoretical treatment, and find, for temperatures up to about 500° Abs., a substantial agreement, although throughout that range the diminution of intensity with temperature is rather less rapid than theory indicates. Above 500° Abs., the observed rate of decrease of intensity is much greater than the theoretical rate. In making the comparison with theory several simplifying assumptions were made which were equivalent to assuming the lattice to consist of only one kind of atom. Now the work of Waller on crystals containing more than one kind of atom shows that it is necessary to consider a separate temperature coefficient for each type.