X-Ray Investigation of the Transition I → II of NH4I at Temperatures Between 22° and -163°C

The lattice parameters of modifications I and II of NH4I at temperatures between 22° and −39°C were determined at twelve different temperatures by using the same Debye-Scherrer method as in the case of NH4Br[1]. At the assumed transition temperature, −16°C, the molar volume was found to increase by 16.96% with increasing temperature.