where f (c, η i ) is the bulk free energy per lattice site, κ c and κ η are the gradient energy coefficients for gradients in composition field c and order parameters η i , respectively, i = 1, 2, ..., n describes n unique grain orientations in the matrix phase. The bulk free energy density f (c, η i ) is constructed in such a way that grains of the matrix phase and second particle phase are in equilibrium with each other across planar surfaces and grain boundaries. We have used the following form for f (c, η i ):