Nucleation and crystallization of WO 3 from pure and Pb 2+ doped NaF fluxes

DTA runs and flux growth experiments have shown that the crystallization temperatures of WO3 from NaF flux are in the range of 1020-1090~ Addition of Pb2+influences the crystal growth and the crystallization temperatures are altered (within this range). A thermal effect giving rise to an exothermal DTA peak was observed above the crystallization temperature. This peak occurs at a higher temperature when lead ions are present. We propose an explana- tion based on pre-crystallization clustering and on the number &nucleation sites on the surface of the platinum crucible.