Phase Transition Properties Of Ferroelectric Thin Films Based On The Transverse Field Ising Model, Two Different Materials

Ferroelectric thin films (PZT, BST, BTO) have piezoelectricity effect, pyroelectric effect, electro-optic effect, acousto-optic effect, photorefractive effect, nonlinear optical effect, and high dielectric speciality. It is worthy of basic research because of ferroelectric thin films'important application value.The main research of the ferroelectric thin film is foucsed on the phase transition of ferroelectric and paraelectric, the Curie temperature and the polarization with the transverse Ising model. However, most of the papers which were published are focused on the study of the phase transition of the usual ferroelectric thin film and the supperlattice. In this paper, we will study the transition properties of the ferroelectric thin film (material-A) with one distinct material layer (material-B) in the middle. Then we will investigate the phase transition properties of the ferroelectric thin film (material-A) with adding seeding-layer (material-B). Finally we will study the phase transition properties of the ferroelectric thin film with two distinct material layers (A/B).The main research contains the following three aspects:(1) By using the Green's function, a recursive equation for the phase transition properties of the ferroelectric thin film (material-A) with one distinct inserting-layer (material B) in the middle was obtained. With the help of this recursive equation, the influence of the exchange interaction JB and the transverse fieldΩ_B of the inserting-layer to the phase diagram were studied systematically; the influence of the exchange interaction JB of the inserting-layer to the crossover value of the transverse fieldΩ_BC was also investigated. Meanwhile, the influence of the exchange interaction JB and the transverse fieldΩ_B of the inserting-layer to the Curie temperature and the polarization of the whole ferroelectric thin film were also shown. It found that when the exchange interaction of the inserting-layer is larger than the bulk's, while the transverse field of the inserting-layer is smaller than the bulk's, all the polarizations of the ferroelectric layers and the curie temperature of the whole ferroelectric thin film will increase obviously. (2) With the help of a recursive equation which is suit for studying the phase transition properties of the ferroelectric thin film with seeding-layer(s), the effect of the whole parameters of the seeding-layerω_B(ω_B =Ω_B/J_B)was studied. Meanwhile, the influence of the exchange interaction JB and the transverse fieldΩ_B of the seeding-layer to the crossover value of the whole parameter of the bulk materialωAC were shown, the influence of the whole parameter of the seeding-layerω_B to the mean polarization and Curie temperature of the ferroelectric thin film were also investigated. The results of the calculation show that the polarization and the Curie temperature will increase prodigious while adding seeding-layer.(3) By applying the recursive equation which is suit for studying the phase transition properties of the ferroelectric thin film with two distince material layers, the influence of the exchange interaction and the transverse field of material-A to the phase diagram were investigated while all the parameters of material-B are fixed. Moreover, the effect of the transverse fieldΩ_A and the exchange interactin JA of material-A on the polarization and Curie temperature were shown. The results show that the phase diagram depends sensitively on the exchange interaction and the transverse field of material-A.