The paper proposes Monte-Carlo method-based 2D and 3D models of vacancies and interstitials in a cubic crystal. The model exploits the concept of lattice gas with covalent bounds between neighbour nodes. Two lattices shifted by half-period serve as nodes for atoms of the main crystal and interstitials. Distribution of particles between both lattices characterizes the entropy of the crystal. Successfully chosen interaction energies between main and sub-lattices allows the authors to detect a phase transition solid-liquid as well as to study the production of crystal defects/their agglomeration as a function of cooling/heating rate. Although the introduced 3D modification of the model contains several rough assumptions, this gives all results of the 2D case as well as reflects some 3D specificities. All the results obtained agree qualitatively with experimental observations on crystals. (C) 2004 Elsevier B.V. All rights reserved.