66 research outputs found
Charge, lattice and magnetism across the valence crossover in EuIrSi single crystals
We present a detailed study of the temperature evolution of the crystal
structure, specific heat, magnetic susceptibility and resistivity of single
crystals of the paradigmatic valence-fluctuating compound EuIrSi. A
comparison to stable-valent isostructural compounds EuCoSi (with
Eu), and EuRhSi, (with Eu) reveals an anomalously large
thermal expansion indicative of the lattice softening associated to valence
fluctuations. A marked broad peak at temperatures around 65-75 K is observed in
specific heat, susceptibility and the derivative of resistivity, as thermal
energy becomes large enough to excite Eu into a divalent state, which localizes
one f electron and increases scattering of conduction electrons. In addition,
the intermediate valence at low temperatures manifests in a moderately
renormalized electron mass, with enhanced values of the Sommerfeld coefficient
in the specific heat and a Fermi-liquid-like dependence of resistivity at low
temperatures. The high residual magnetic susceptibility is mainly ascribed to a
Van Vleck contribution. Although the intermediate/fluctuating valence duality
is to some extent represented in the interconfiguration fluctuation model
commonly used to analyze data on valence-fluctuating systems, we show that this
model cannot describe the different physical properties of EuIrSi with
a single set of parameters.Comment: 12 pages, 4 figures, 1 tabl
Single crystal growth and anisotropic magnetic properties of Li2Sr[Li1 â xFexN]2
Up to now, investigation of physical properties of ternary and higher
nitridometalates was severely hampered by challenges concerning phase purity
and crystal size. Employing a modified lithium flux technique, we are now able
to prepare sufficiently large single crystals of the highly air and moisture
sensitive nitridoferrate for anisotropic
magnetization measurements. The magnetic properties are most remarkable: large
anisotropy and coercivity fields of 7 Tesla at K indicate a significant
orbital contribution to the magnetic moment of iron. Altogether, the novel
growth method opens a route towards interesting phases in the comparatively
recent research field of nitridometalates and should be applicable to various
other materials.Comment: 10 pages, 5 figures, published open access in Inorganics, minor typos
correcte
Structural investigations of CeIrIn and CeCoIn on macroscopic and atomic length scales
For any thorough investigation of complex physical properties, as encountered
in strongly correlated electron systems, not only single crystals of highest
quality but also a detailed knowledge of the structural properties of the
material are pivotal prerequisites. Here, we combine physical and chemical
investigations on the prototypical heavy fermion superconductors CeIrIn
and CeCoIn on atomic and macroscopic length scale to gain insight into
their precise structural properties. Our approach spans from enhanced
resolution X-ray diffraction experiments to atomic resolution by means of
Scanning Tunneling Microscopy (STM) and reveal a certain type of local features
(coexistence of minority and majority structural patterns) in the tetragonal
HoCoGa-type structure of both compounds.Comment: 8 pages, 5 figures, submitted to JPSJ (SCES 2013
Refinement of the crystal structure of palladium gallium (1:1), PdGa
PdGa, cubic, P2(1)3 (no. 198), a = 4.89695(6) angstrom, V = 117.
Crystal structure of cobalt manganese monoaqua catena-[monohydrogenborate-tris(hydrogenphosphate)], (Co0.6Mn0.4)(2)(H2O) [BP3O9(OH)(4)]
BCo1.20H6Mn0.80O14P3, orthorhombic, P2(1)2(1)2(1) (no. 19), a = 7.1355(6) angstrom, b = 8.7321(8) angstrom, c = 16.405(2) angstrom, V = 1022.2 angstrom(3), Z = 4, R-gt(F) = 0.049, wR(ref)(F-2) = 0. 119, T = 295 K
Tricyanidoferrates(âIV) and ruthenates(âIV) with nonâinnocent cyanido ligands
Exceptionally electron-rich, nearly trigonal-planar tricyanidometalate anions [Fe(CN)(3)](7-) and [Ru(CN)(3)](7-) were stabilized in LiSr3[Fe(CN)(3)] and AE(3.5)[M(CN)(3)] (AE=Sr, Ba; M=Fe, Ru). They are the first examples of group 8 elements with the oxidation state of -IV. Microcrystalline powders were obtained by a solid-state route, single crystals from alkali metal flux. While LiSr3[Fe(CN)(3)] crystallizes in P6(3)/m, the polar space group P6(3) with three-fold cell volume for AE(3.5)[M(CN)(3)] is confirmed by second harmonic generation. X-ray diffraction, IR and Raman spectroscopy reveal longer C-N distances (124-128 pm) and much lower stretching frequencies (1484-1634 cm(-1)) than in classical cyanidometalates. Weak C-N bonds in combination with strong M-C pi-bonding is a scheme also known for carbonylmetalates. Instead of the formal notation [Fe-IV(CN-)(3)](7-), quantum chemical calculations reveal non-innocent intermediate-valent CN1.67- ligands and a closed-shell d(10) configuration for Fe, that is, Fe2-
Nanoporous titanium borophosphates with rigid gainesite-type framework structure
China Scholarship Council (CSC); National Natural Science Foundation of China [40972035]Nanoporous titanium borophosphates have been synthesized which exhibit a rigid gainesite-type framework of polyhedra. The open-framework character is supported by the reversibility of de-and rehydration processes
Ultrasmall functional ZnO2 nanoparticles: synthesis, characterization and oxygen release properties
Ultrasmall zinc peroxide nanoparticles with diameter between 3.3 +/- 0.9 and 14.4 +/- 5.2 nm were synthesized by a simple and fast hydrothermal synthesis method. The precursor zinc acetate dihydrate was oxidized with hydrogen peroxide in aqueous media using a high-pressure impinging-jet reactor (MRT CR5, Microfluidics (R)). The combination of the high process pressure of 1400 bar and the special reaction chamber geometry minimized nanoparticle aggregation and limited the crystal growth, which resulted in very small and uniform particles. The zinc peroxide nanoparticles were in situ stabilized by bis[2-(methacryloyloxy)ethyl]phosphate providing excellent colloidal stability in water and integration of functional groups (polymerizable vinyl groups and adhesion-promoting phosphate groups). The obtained nanoparticles were characterized by XRD, TGA, TGA-MS, TEM, HR-TEM, Raman spectroscopy and zeta potential measurements. Furthermore the oxygen release from ZnO2 nanoparticles was analyzed. The oxygen release can be triggered by two different mechanisms: thermal decomposition in the dry state (T < 190 degrees C) and hydrolysis in water at pH < 8
Anomalous Thermal Expansion of HoCo0.5Cr0.5O3 Probed by X-ray Synchrotron Powder Diffraction
Abstract Mixed holmium cobaltite-chromite HoCo0.5Cr0.5O3 with orthorhombic perovskite structure (structure type GdFeO3, space group Pbnm) was obtained by solid state reaction of corresponding oxides in air at 1373Â K. Room- and high-temperature structural parameters were derived from high-resolution X-ray synchrotron powder diffraction data collected in situ in the temperature range of 300â1140Â K. Analysis of the results obtained revealed anomalous thermal expansion of HoCo0.5Cr0.5O3, which is reflected in a sigmoidal temperature dependence of the unit cell parameters and in abnormal increase of the thermal expansion coefficients with a broad maxima near 900Â K. Pronounced anomalies are also observed for interatomic distances and angles within Co/CrO6 octahedra, tilt angles of octahedra and atomic displacement parameters. The observed anomalies are associated with the changes of spin state of Co3+ ions and insulator-metal transition occurring in HoCo0.5Cr0.5O3
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