Abstract
This paper investigates the phase diagrams of a ferroelectric thin film described by the transverse Ising model with a four-spin interaction. Within the framework of the higher decoupling approximation, the phase diagrams for the first-order and second-order transitions in a ferroelectric thin film are obtained, respectively, while increasing and decreasing temperature. The effects of various parameters and film thickness on the phase diagrams are shown, and the comparison between the higher decoupling approximation and the usual mean-field approximation is illustrated.