Electrical and thermal investigations of the phase transitions in ammonium purpurate “murexide” C 8H 4O 6N 5 · HN 4

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 8H 4O 6H 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.