Ferroelectricity in PbTiO{sub}3 thin films: a first principles approach

摘要

The ground-state ferroelectric distortion of PbTiO{sub}3 thin films is studied using a first-principles effective Hamiltonian to describe the structural energetics at a microscopic level. Under short-circuit electrical and zero-stress mechanical boundary conditions, (001) films as thin as one unit cell are found to support a stable perpendicular polarization. Size effects in the layer-by-layer ferroelectric distortion are discussed. The continuum limit of the first-principles effective Hamiltonian has the same form as the widely-used Landau-Ginzburg expression for the free energy near T{sub}c, so that the present results can be directly related to those of previous phenomenological studies. In particular, a microscopic interpretation of the extrapolation length δ is proposed.