412 research outputs found
Epitaxially stabilized iridium spinel oxide without cations in the tetrahedral site
Single-crystalline thin film of an iridium dioxide polymorph Ir2O4 has been
fabricated by the pulsed laser deposition of LixIr2O4 precursor and the
subsequent Li-deintercalation using soft chemistry. Ir2O4 crystallizes in a
spinel (AB2O4) without A cations in the tetrahedral site, which is
isostructural to lambda-MnO2. Ir ions form a pyrochlore sublattice, which is
known to give rise to a strong geometrical frustration. This Ir spinel was
found to be a narrow gap insulator, in remarkable contrast to the metallic
ground state of rutile-type IrO2. We argue that an interplay of strong
spin-orbit coupling and a Coulomb repulsion gives rise to an insulating ground
state as in a layered perovskite Sr2IrO4.Comment: 9 pages, 3 figure
Comparison of crystal structures and effects of Co substitution in a new member of Fe-1111 superconductor family AeFeAsF(Ae = Ca and Sr): a possible candidate for higher Tc superconductor
We refined crystal structures of newly found members of the Fe-1111
superconductor family, CaFe\_{1-x}Co\_{x}AsF and SrFe\_{1-x}Co\_{x}AsF (x = 0,
0.06, 0.12) by powder synchrotron X-ray diffraction analysis. The tetragonal to
orthorhombic phase transitions were observed at ~120 K for unsubstituted
CaFeAsF and at ~180 K for unsubstituted SrFeAsF, the transition temperatures
agreeing with kinks observed in temperature-dependent resistivity curves.
Although the transition temperature decreases, the structural phase transitions
were observed below 100 K in both samples of x = 0.06, and finally they were
suppressed in the doping level of x = 0.12. The refined structures reveal that
distortions of the FeAs4 tetrahedron from the regular tetrahedron likely
originate from mismatches in atomic radii among the constituent elements. In
this system, the enlarged FeAs4 tetrahedron resulting from larger radius of Sr
than that of Ca is flattened along a-b plane, whereas the smaller radius of Ca
makes the tetrahedron closer to regular one, and their characteristic shapes
are further enhanced by Co substitution. These results suggest that the CaFeAsF
compound is a promising candidate for higher-Tc superconductor.Comment: 17 pages, 8 figures, 2 tables, Supplementary information is included
at the end of the documen
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