ELECTRICAL AND THERMAL INVESTIGATIONS OF THE PHASE-TRANSITIONS IN AMMONIUM PURPURATE MUREXIDE C8H4O6N5.HN4

Based on some electrical properties (resistivity, dielectric constant and pyroelectric current) measured between 40 and 300-degrees-C, combined with the DTA thermogram in the same temperature range, we observed two structural phase transitions in ammonium purpurate (APP) ``murexide{''} C8H4O6H5.NH4 at temperatures of about 100 and 257-degrees-C. The data are correlated to the reorientation and distortion of the NH4 ions, which are closely related to the different possibilities of the N-H...X hydrogen bonding scheme.