87 research outputs found
Paradoxical reaction in non HIV-tuberculosis, a rare case with pancreatic involvement
A 24-year-old young man presents a sudden hepatic cytolysis and cholestasis after two months of isoniazid, rifampin and pyrazinamide therapy for severe lung tuberculosis. Initial data included heroin consumption history, HIV-negative serology, drug sensitivity and a normal abdominal CT
EXAFS study of lead-free relaxor ferroelectric BaTi(1-x)Zr(x)O3 at the Zr K-edge
Extended X-ray absorption fine structure (EXAFS) experiments at the Zr K-edge
were carried out on perovskite relaxor ferroelectrics BaTi(1-x)Zr(x)O3 (BTZ) (x
= 0.25, 0.30, 0.35), and on BaZrO3 for comparison. Structural information up to
4.5 A around the Zr atoms is obtained, revealing that the local structure
differs notably from the average Pm-3m cubic structure deduced from X-ray
diffraction. In particular, our results show that the distance between Zr atoms
and their first oxygen neighbors is independent of the Zr substitution rate x
and equal to that measured in BaZrO3, while the X-ray cubic cell parameter
increases linearly with x. Furthermore, we show that the Zr atoms tend to
segregate in Zr-rich regions. We propose that the relaxor behavior in BTZ is
linked to random elastic fields generated by this particular chemical
arrangement, rather than to random electric fields as is the case in most
relaxors.Comment: 13 pages, 12 figures, 4 tables. Submitted to Phys. Rev.
Investigation of the Jahn-Teller Transition in TiF3 using Density Functional Theory
We use first principles density functional theory to calculate electronic and
magnetic properties of TiF3 using the full potential linearized augmented plane
wave method. The LDA approximation predicts a fully saturated ferromagnetic
metal and finds degenerate energy minima for high and low symmetry structures.
The experimentally observed Jahn-Teller phase transition at Tc=370K can not be
driven by the electron-phonon interaction alone, which is usually described
accurately by LDA.
Electron correlations beyond LDA are essential to lift the degeneracy of the
singly occupied Ti t2g orbital. Although the on-site Coulomb correlations are
important, the direction of the t2g-level splitting is determined by the
dipole-dipole interactions. The LDA+U functional predicts an aniferromagnetic
insulator with an orbitally ordered ground state. The input parameters U=8.1 eV
and J=0.9 eV for the Ti 3d orbital were found by varying the total charge on
the TiF ion using the molecular NRLMOL code. We estimate the
Heisenberg exchange constant for spin-1/2 on a cubic lattice to be
approximately 24 K. The symmetry lowering energy in LDA+U is about 900 K per
TiF3 formula unit.Comment: 7 pages, 9 figures, to appear in Phys. Rev.
Influence of Zr-substitution on phase transitions character in polycrystalline Ba(Ti1−x Zr x )O3
Nouvelles phases oxyfluorees ferroelectriques non-stoechiometriques derivees de LiNbO3 et de LiTaO3
Correlations between sintering conditions and microstructure in ceramics of composition Li 0.80
Optical and dielectric studies on ferroelectric oxyfluoride K<sub>3</sub>MoO<sub>3</sub>F<sub>3</sub> single crystals
Ferroelec. oxyfluoride K3MoO3F3 single crystals prepd. by the Bridgman method were studied by means of polarized light microscopy and dielec. measurements. Anal. of the ferroelastic domains indicate a first order phase transition at TC = 528 K from a ferroic phase to a cubic (m.hivin.3m) one. Domain structures are consistent with a trigonal symmetry below TC. Continuous measurements of the temp. dependence of birefringence and dielec. permittivity between 300 and 600 K led to the disclosure of an addnl. phase transition of 1st-order at T1 = 453 K
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