X-RAY AND DILATOMETRIC INVESTIGATIONS ON THE DISORDER IN STRONTIUM CHLORIDE

SrCl//2 crystallizes in the fluorite structure and shows, like all materials with this structure, anomal properties with regard to thermodynamic as well as to transport phenomena. In a temperature region starting about 200 K below the melting point (1146 K) a pronounced maximum of c//p is found, which is to be identified with a Schottky anomaly. Most significant are the increasing values of ionic conductivity with rising temperture. They mostly exceed those of a typical ionic melt. The degree of the 'molten' anion lattice and the distinct places of the defect ions are not clarified until now. The temperature of transition at the maximum of the expansion coefficient value at T equals 1000 K has been determined by dilatometric measurements. The existence of predominant Frenkel-disorder has been demonstrated by comparing X-ray and dilatometric measurements. The ratio of ionic radii relative to the configuration in the fluorite structure has been determined from lattice parameter and the crystal structure.