Abstract
The antisymmetrical interaction between nearest-neighbours in a statistical lattice model with two Ising variables can stabilize the long-period modulations of the order parameter. The range of stability of phases with the modulation period up to 13 lattice constants was found numerically in the molecular-field approximation. The model is supposed to explain the mechanism of transitions to long-period as well as incommensurate structures in A'A"BX4-type compounds.