181 research outputs found
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 EuTiO 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.Comment: Significantly revised for clarit
Ferroelectricity in the Dion-Jacobson CsBiNbO from first principles
We have studied ferroelectricity in Dion-Jacobson CsBiNbO 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 CsBiNbO is a ferroelectric with a polarization
of P=40C cm. We propose further experiments to clarify this
point
Coupled magnetic-ferroelectric metal-insulator transitions in epitaxially-strained SrCoO from first principles
First-principles calculations of the epitaxial-strain phase diagram of
perovskite SrCoO 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
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