Electrical and thermal investigations of the phase transitions in ammonium purpurate “murexide” C8H4O6N5 · HN4

Abstract Based on some electrical properties (resistivity, dielectric constant and pyroelectric current) measured between 40 and 300°C, combined with the DTA thermogram in the same temperature range, we observed two structural phase transitions in ammonium purpurate (APP) “murexide’ C 8 H 4 O 6 H 5 · NH 4 at temperatures of about 100 and 257°C. The data are correlated to the reorientation and distortion of the NH 4 ions, which are closely related to the different possibilities of the N-H … X hydrogen bonding scheme.