UNUSUALLY STRONG DEFORMATION OF GUANIDINIUM NITRATE CRYSTAL AT THE SOLID SOLID-PHASE TRANSITION

A phase transition has been observed in the guanidinium nitrate crystals. By using the DTA method, a presence of strong endothermic and exothermic anomaly was proved to occur at 296 K and 276 K respectively. Both the character of the thermal changes and a 20-degree temperature hysteresis indicate that the observed phase transition is of the first order and it is accompanied by spectacular changes in the shape of the crystals. Dilatometric measurements proved that at the transition from the low- to the high-temperature phase, the length of needle-shaped crystal of guanidinium nitrate increases by about 45%, while the transverse dimensions decrease, though the crystal is not destroyed. The phase transition is also accompanied by the changes in dielectric permittivity.