7,984 research outputs found
On the nature of change in Ni oxidation state in BaTiO3-SrTiO3 system
XAFS studies of Ni-doped BaSrTiO solid solution reveal that
the Ni oxidation state changes from 4 in SrTiO to 2.5 in BaTiO when
varying . This change is accompanied by a noticeable change in the
interatomic Ni-O distances in the first shell. The first-principles
calculations show that nickel creates an impurity band in the forbidden band
gap of BaTiO and SrTiO, which explains the appearance of intense
absorption of Ni-doped samples in the visible region. The analysis of the
electronic structure of doped crystals and calculations of the oxygen vacancy
formation energy in them show that different oxidation states of Ni in
SrTiO and BaTiO can be explained by different formation energies of the
oxygen vacancies in these compounds.Comment: 5 pages, 2 figures, 1 tabl
An experimental and theoretical study of Ni impurity centers in BaSrTiO
The local environment and the charge state of a nickel impurity in cubic
BaSrTiO are studied by XAFS spectroscopy. According to the
XANES data, the mean Ni charge state is 2.5+. An analysis of the EXAFS
spectra and their comparison with the results of first-principle calculations
of the defect geometry suggest that Ni ions are in a high-spin state at
the sites of the perovskite structure and the difference of the Ni
and Ti charges is mainly compensated by distant oxygen vacancies. In
addition, a considerable amount of nickel in the sample is in a second phase
BaNiO. The measurements of the lattice parameter show a decrease
in the unit cell volume upon doping, which can indicate the existence of a
small amount of Ni ions at the sites.Comment: 8 pages, 3 figures, 3 table
When a C*-algebra is a coefficient algebra for a given endomorphism
The paper presents a criterion for a C*-algebra to be a coefficient algebra
associated with a given endomorphis
Shape transformations in rotating ferrofluid drops
Floating drops of magnetic fluid can be brought into rotation by applying a
rotating magnetic field. We report theoretical and experimental results on the
transition from a spheroid equilibrium shape to non-axissymmetrical three-axes
ellipsoids at certain values of the external field strength. The transitions
are continuous for small values of the magnetic susceptibility and show
hysteresis for larger ones. In the non-axissymmetric shape the rotational
motion of the drop consists of a vortical flow inside the drop combined with a
slow rotation of the shape. Nonlinear magnetization laws are crucial to obtain
quantitative agreement between theory and experiment.Comment: 4 pages, 3 figure
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