Röntgenographische und dilatometrische Untersuchungen zur Fehlordnung im Strontiumchlorid

Abstract

Gitterfehlordnung / Kristallstruktur / PhasenumwandlungenSrCI2 cristallizes in the fluorite structure and shows, like all materials with this structure, anomal properties with regard t o thermodynamic as well as to transport phenomena. In a temperature region starting about 200 K below the melting point (1 146 K) a pronounced maximum of cp is found, which ic to be identified with a Schottky anomaly. Most significant are the increasing values of ionic conductivity with rising temperature. 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 = lo00 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.The enthalpy of formation of Frenkel disorder has been calculated from dilatometric measurements to AHf = (248 k 8) kJ mol.