61 research outputs found
Surface polar states and pyroelectricity in ferroelastics induced by flexo-roto field
Theoretical analysis based on the Landau-Ginzburg-Devonshire (LGD) theory is
used to show that the joint action of flexoelectric effect and rotostriction
leads to a large spontaneous in-plane polarization (~ 1-5 muC/cm2) and
pyroelectric coefficient (~10^-3 C/m2K) in the vicinity of surfaces of
otherwise non-ferroelectric ferroelastics, such as SrTiO3, with static
octahedral rotations. The origin of the improper polarization and
pyroelectricity is an electric field we name flexo-roto field whose strength is
proportional to the convolution of the flexoelectric and rotostriction tensors
with octahedral tilts and their gradients. Flexo-roto field should exist at
surfaces and interfaces in all structures with static octahedral rotations, and
thus it can induce surface polar states and pyroelectricity in a large class of
otherwise nonpolar materials.Comment: 16 pages, 3 figures, 1 table, supplementary material
Interfacial Polarization and Pyroelectricity in Antiferrodistortive Structures Induced by a Flexoelectric Effect and Rotostriction
Theoretical analysis based on the Landau-Ginzburg-Devonshire (LGD) theory is
used to show that the product effect of flexoelectricity and rotostriction can
lead to a spontaneous polarization in the vicinity of antiphase boundaries,
ferroelastic twin walls, surfaces and interfaces in the octahedrally tilted
phase of otherwise non-ferroelectric perovskites such as CaTiO3, SrTiO3, and
EuTiO3. As an example, we numerically demonstrate a large spontaneous
polarization on the order of 1-5muC/cm2 at the SrTiO3 antidistortive phase
boundaries at temperatures lower than the antiferrodistortive structural phase
transition temperature of ~105 KComment: 61 page, 24 figures, 1 table; Extended version including twin domain
wall
Spin singlet small bipolarons in Nb-doped BaTiO3
The magnetic susceptibility and electrical resistivity of n-type
BaTi{1-x}Nb{x}O3 have been measured over a wide temperature range. It is found
that, for 0 < x < 0.2, dopant electrons form immobile spin singlet small
bipolarons with binding energy around 110 meV. For x = 0.2, a maximum in the
electrical resistivity around 15 K indicates a crossover from band to hopping
transport of the charge carriers, a phenomenon expected but rarely observed in
real polaronic systems.Comment: 5 pages, 4 figure
Comment on ``Conduction states in oxide perovskites: Three manifestations of Ti Jahn-Teller polarons in barium titanate''
In this comment to [S. Lenjer, O. F. Schirmer, H. Hesse, and Th. W. Kool,
Phys. Rev. B {\bf 66}, 165106 (2002)] we discuss the electronic structure of
oxygen vacancies in perovskites. First principles computations are in favour of
rather deep levels in these vacancies, and Lenjer et al suggest that the
electrons' interaction energy is negative, but data on electroconductivity are
against.Comment: 2 pages, no figure
Role of gallium diffusion in the formation of a magnetically dead layer at the Y3Fe5O12/Gd3Ga5O12 epitaxial interface
We have clarified the origin of a magnetically dead interface layer formed in yttrium iron garnet (YIG) films grown at above 700 degrees C onto a gadolinium gallium garnet (GGG) substrate by means of laser molecular beam epitaxy. The diffusion-assisted formation of a Ga-rich region at the YIG/GGG interface is demonstrated by means of composition depth profiling performed by x-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and x-ray and neutron reflectometry. Our finding is in sharp contrast to the earlier expressed assumption that Gd acts as a migrant element in the YIG/GGG system. We further correlate the presence of a Ga-rich transition layer with considerable quenching of ferromagnetic resonance and spin wave propagation in thin YIG films. Finally, we clarify the origin of the enigmatic low-density overlayer that is often observed in neutron and x-ray reflectometry studies of the YIG/GGG epitaxial system
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