A monotectic and a eutectic organic alloy have been synthesized with the help of phase diagram study. The phase diagram of an organic analogue of a metal-nonmetal system involving succinonitrile-1,4-diiodobenzene shows two immiscible liquid phases are in equilibrium with a single liquid phase. Growth behaviour of the eutectic, the monotectic and the pure components, studied at different under-cooling temperatures, suggests that the data obey the square relationship between growth velocity and under-coolings. The thermal study such as heat of mixing, entropy of fusion, roughness parameter, interfacial energy and excess thermodynamic functions were calculated via the enthalpy of fusion values, determined using differential scanning calorimeter (DSC) method. The effects of solid-liquid interfacial energy on morphology of monotectic have also been discussed. The microstructures of monotectic, eutectic and pure components show their peculiar characteristic features. (C) 2009 Elsevier B.V. All rights reserved.