Polymorphic and pressure-induced phase transformations of malonamide system

• We discuss the influence of the variation of temperature and pressure.
• We describe the stability domains of the three polymorphs of malonamide.
• Both concepts of monotropy and enantiotropy are developed for this diagram.
• We deduce the most likely case pressure–temperature diagram.
• Increasing the pressure, a negative slope is found for the M–Q equilibrium curve.

Three polymorphs are involved in the construction of the phase diagram describing the enantiotropic and monotropic behavior of the malonamide system, discussed as a function of the temperature and the pressure. The few data available on the orthorhombic metastable form fosters discussion about the domain of stability of this polymorph and about the pressure-induced phase transformation. But previous calculations carried out on this system, along with the method presented here allow proposing the most probable stable phase diagram of malonamide.

The schematic P–T phase diagram of malonamide involving the three polymorphs: stability domain or not for the orthorhombic phase?Figure optionsDownload as PowerPoint slide