Interfacial Tension and Size Dependence of the Critical Temperature of the Domain Structure of Displacement-Type Ferroelectrics

摘要

The presence of the domain boundary changes the nature of the distribution of the system components in the near-surface region compared to their distribution in the volume of the phase, which makes the overall system inhomogeneous. Size dependence of critical temperature T-crit(L), where L is the size of the side of the cube, is due to the limited volume of the domain, when the contribution of the surface is significant in the thermodynamic functions of the substance. To calculate the surface properties of interfaces and size dependence T-crit(L) of the domain structure of displacement-type ferroelectrics, the lattice gas model (LGM) was used. The possibility of using this model is due to the concept of a two-well potential for mobile ion A in the so-called "single-ion model" of a diatomic crystal lattice of AB type. The LGM describes the distribution of displacement-type ferroelectric ions using the concept of effective pair energy parameters of the interionic interaction, which are determined from the bulk properties of the crystal. If these parameters are known, the LGM allows one to proceed to the description of the properties of bias ferroelectrics, taking into account the limited size of the domain. The calculation of interfacial tensions and dependence T-crit(L) was carried out in the quasi-chemical approximation, taking into account the correlated distribution of neighboring ions. The temperature dependences of interfacial tensions on the mutual orientation of neighboring phases are considered. It is found that the T-crit(L) dependence decreases as linear size of the cubic domain L decreases. The correspondence between the calculated T-crit(L) dependence and the experimental data is discussed.