240 research outputs found
Physical properties and lattice dynamics of bixbyite-type V2O3
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Some time ago, we reported the synthesis of bixbyite-type V2O3, a new metastable polymorph of vanadium sesquioxide. Since, a number of investigations followed, dealing with different aspects like electronic and magnetic properties of the material, the deviation from ideal stoichiometry or the preparation of nanocrystals as oxygen storage material. However, most of the physical properties were only evaluated on a theoretical basis. Here, we report the lattice dynamics and physical properties of bixbyite-type V2O3 bulk material, which we acquired from physical property measurements and neutron diffraction experiments over a wide temperature range. Besides attributing different possible orientations of the magnetic moments for V1 and V2 to the identified antiferromagnetic (AFM) ground state with a Néel temperature of 38.1(5) K, we use a first order Grüneisen approximation to determine lattice-dependent parameters for the relatively stiff cubic lattice, and, amongst others identify the Debye temperature to be as low as 350 ± 65 K.DFG, 73789094, SPP 1415: Kristalline Nichtgleichgewichtsphasen - Präparation, Charakterisierung und in situ-Untersuchung der Bildungsmechanisme
Magnetostrictive Neel ordering of the spin-5/2 ladder compound BaMn2O3: distortion-induced lifting of geometrical frustration
The crystal structure and the magnetism of BaMnO have been studied by
thermodynamic and by diffraction techniques using large single crystals and
powders. BaMnO is a realization of a spin ladder as the
magnetic interaction is dominant along 180 Mn-O-Mn bonds forming the
legs and the rungs of a ladder. The temperature dependence of the magnetic
susceptibility exhibits well-defined maxima for all directions proving the
low-dimensional magnetic character in BaMnO. The susceptibility and
powder neutron diffraction data, however, show that BaMnO exhibits a
transition to antiferromagnetic order at 184 K, in spite of a full frustration
of the nearest-neighbor inter-ladder coupling in the orthorhombic
high-temperature phase. This frustration is lifted by a remarkably strong
monoclinic distortion which accompanies the magnetic transition.Comment: 9 pages, 8 figures, 2 tables; in V1 fig. 2 was included twice and
fig. 4 was missing; this has been corrected in V
Mechanisms Involved in Calcium-Dependent Exocytosis a
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74760/1/j.1749-6632.1991.tb36506.x.pd
Canted antiferromagnetism in phase-pure CuMnSb
We report the low-temperature properties of phase-pure single crystals of the
half-Heusler compound CuMnSb grown by means of optical float-zoning. The
magnetization, specific heat, electrical resistivity, and Hall effect of our
single crystals exhibit an antiferromagnetic transition at and a second anomaly at a temperature . Powder and single-crystal neutron diffraction establish an
ordered magnetic moment of ,
consistent with the effective moment inferred from the Curie-Weiss dependence
of the susceptibility. Below , the Mn sublattice displays
commensurate type-II antiferromagnetic order with propagation vectors and
magnetic moments along (magnetic space group ).
Surprisingly, below , the moments tilt away from by
a finite angle , forming a canted antiferromagnetic
structure without uniform magnetization consistent with magnetic space group
. Our results establish that type-II antiferromagnetism is not the
zero-temperature magnetic ground state of CuMnSb as may be expected of the
face-centered cubic Mn sublattice.Comment: 14 pages, 15 figure
Computational study of LnGaO3 (Ln=La+Gd) perovskites
Atomistic simulation techniques have been used to study the thermal properties of perovskite-type LnGaO3 (Ln = La-Gd). A set of interatomic potentials describing interatomic interactions in these compounds was developed and tested over a wide temperature range through utilizing free energyminimization.The predicted dielectric constants, thermal expansion coefficients, phonon density of states and its projections, heat capacity and entropy, elastic moduli, Gruneisen parameters, surface energies for main crystallographic directionsand Debye temperatures are in good agreement with the limited available experimental data. Perovskite-type LnGaO3 (Ln = La-Gd) compounds have been examined under conditions to which substrate materials are typically subjected. Only a narrow region in the phase diagram of LnGaO3 (Ln = La-Gd) and their solid solutions is recommended for use in substrate applications
Origin of Ferroelectricity in Orthorhombic LuFeO
We demonstrate that small but finite ferroelectric polarization (0.01
C/cm) emerges in orthorhombic LuFeO () at (600
K) because of commensurate (k = 0) and collinear magnetic structure. The
synchrotron x-ray and neutron diffraction data suggest that the polarization
could originate from enhanced bond covalency together with subtle contribution
from lattice. The theoretical calculations indicate enhancement of bond
covalency as well as the possibility of structural transition to the polar
phase below . The phase, in fact, is found to be
energetically favorable below in orthorhombic LuFeO ( with
very small energy difference) than in isostructural and nonferroelectric
LaFeO or NdFeO. Application of electric field induces finite
piezostriction in LuFeO via electrostriction resulting in clear domain
contrast images in piezoresponse force microscopy.Comment: 12 pages, 8 figure
Lithium Diffusion and Diffraction
In the current contribution the application of bond valence method for the prediction (and diffraction-based techniques for the evalution) of ion diffusion pathways in different materials
for electrochemical energy conversion and storage will be presented and discussed
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