title: The role of mechanical boundary conditions in the soft mode dynamics of PbTiO3.
abstract: The role of different mechanical boundary conditions in the soft mode dynamics of ferroelectric PbTiO3 is systematically investigated using first-principles-based simulations and analytical model. The change in the soft mode dynamics due to hydrostatic pressure, uniaxial and biaxial stresses and biaxial strains is studied in a wide temperature range. Our computations predict: (i) the existence of Curie-Weiss laws that relate the soft mode frequency to the stress or strain; (ii) a non-trivial temperature evolution of the associated Curie-Weiss constants; (iii) a qualitative difference between the soft mode response to stresses/strains and hydrostatic pressure. The latter finding implies that the Curie-Weiss pressure law commonly used for residual stress estimation may not apply for the cases of uniaxial and biaxial stresses and strains. On the other hand, our systematic study offers a way to eliminate this difficulty through the establishment of Curie-Weiss stress and strain laws. Implications of our predictions for some available experimental data are discussed.
authors.affiliation: Department of Physics, University of South Florida, Tampa, FL 33620, USA.
authors.forename: Kevin
authors.initials: K
authors.lastname: McCash
authors.forename: B K
authors.initials: BK
authors.lastname: Mani
authors.forename: C-M
authors.initials: CM
authors.lastname: Chang
authors.forename: I
authors.initials: I
authors.lastname: Ponomareva