A back-reflection x-ray camera for thermal-expansion studies and the thermal expansion of NaCl from −180°C to 200°C

Abstract

This paper describes a simple back-reflection x-ray camera for thermal studies from –180°C to 200°C. This is a modification of the Unicam singlecrystal goniometer S 25. The camera effectively eliminates any temperature gradient along the length of the specimen and the temperature can be maintained constant to ± 0.5°C. The deposition of ice on the specimen at low temperatures is also successfully prevented. Using this camera the lattice thermal expansion of melt-grown single crystals of NaCl was measured over the range –180° to 200°C. These results are in very good agreement with the macroscopic thermal expansion of the same batch of crystals made by Dr. R. Srinivasan, as also those obtained by other authors for this substance. This agreement suggests that if lattice defects are present in NaCl at room temperature they must be uniformly distributed throughout the volume of the crystal.