Configuration dependence of physical properties of a ferroelectric solid solution

In this article, we motivate the detailed comparison of the physical properties of individual configurations of a ferroelectric solid solution as a means toward developing first principles models for these systems. We compare energies, dielectric constants epsilon_infinity, mode effective charges of local polar distortions, and the zero temperature piezoelectric behavior of several ordered Pb_3GeTe_4 supercells. Cluster expansions of these properties show the importance of second-neighbor effects, which can be related to symmetry-preserving relaxation and its effect on the symmetry breaking polar instabilities.Comment: 11 pages, LaTeX (aipproc), 1 eps figur

Temperature-dependent dielectric and piezoelectric response of ferroelectrics from first principles

A method for the calculation of the temperature dependence of dielectric and piezoelectric responses, based on the use of a first-principles effective Hamiltonian, is described. Results are presented for the ferroelectric perovskite PbTiO3. While the method includes only the soft-mode contributions to the responses, it is argued to give a good description of the divergences or near-divergences of the response functions near the cubic-tetragonal transition. The expression of the response functions in terms of correlation functions is used to provide a real-space interpretation of the responses which clearly distinguishes between PbTiO3 and the related materials BaTiO3 and KNbO3.Comment: 10 pages, LaTeX (aipproc), three eps figure

Magnetic and electric phase control in epitaxial EuTiO3_3 from first principles

We propose a design strategy - based on the coupling of spins, optical phonons, and strain - for systems in which magnetic (electric) phase control can be achieved by an applied electric (magnetic) field. Using first-principles density-functional theory calculations, we present a realization of this strategy for the magnetic perovskite EuTiO$_3$.Comment: Significantly revised for clarit

Ferroelectricity in the Dion-Jacobson CsBiNb2_2O7_7 from first principles

We have studied ferroelectricity in Dion-Jacobson CsBiNb$_2$O$_7$ from first principles. Using group-theoretical analysis and first-principles density functional calculations of the total energy and phonons, we perform a systematic study of the energy surface around a paraelectric prototypic phase. Our results suggest that CsBiNb$_2$O$_7$ is a ferroelectric with a polarization of P$_s$=40$\mu$C cm$^{-2}$. We propose further experiments to clarify this point

Coupled magnetic-ferroelectric metal-insulator transitions in epitaxially-strained SrCoO3_{3} from first principles

First-principles calculations of the epitaxial-strain phase diagram of perovskite SrCoO$_{3}$ are presented. Through combination of the large spin-phonon coupling with polarization-strain coupling and coupling of the band gap to the polar distortion, both tensile and compressive epitaxial strain are seen to drive the bulk ferromagnetic-metallic (FM-M) phase to antiferromagnetic-insulating-ferroelectric (AFM-I-FE) phases, the latter having unusually low elastic energy. At these coupled magnetic-ferroelectric metal-insulator phase boundaries, cross responses to applied electric and magnetic fields and stresses are expected. In particular, a magnetic field or compressive uniaxial stress applied to the AFM phases could induce an insulator-metal transition, and an electric field applied to the FM-M phase could induce a metal-insulator transition.Comment: 2 figures and 1 tabl