| 1. |
- Reim, J. D., et al.
(author)
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Structural invariance upon antiferromagnetic ordering in geometrically frustrated swedenborgite, CaBaCo2Fe2O7
- 2014
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In: Journal of Applied Crystallography. - 1600-5767. ; 47, s. 2038-2047
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Journal article (peer-reviewed)abstract
- Centimetre-sized single crystals of high-quality CaBaCo2Fe2O7 were synthesized by the optical floating zone technique. The metal-to-metal stoichiometry and oxygen content were confirmed by spectroscopy and thermal reduction experiments. The hexagonal symmetry P6(3)mc (No. 186) well describes the powder X-ray and neutron diffraction as well as single-crystal neutron diffraction at all measured temperatures. This symmetry is also consistent with optical second harmonic generation data obtained between 10 and 295 K. However, a satisfactory structure description from single-crystal neutron diffraction data needs an oxygen split position. Specific heat, magnetic susceptibility and powder neutron diffraction data indicate a magnetic phase transition at T-N = 159 K to an antiferromagnetic ground state, but with a persisting hexagonal symmetry and intrinsic geometric frustration.
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| 2. |
- Ghorbani, Shaban Reza, et al.
(author)
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Thermoelectric power and resistivity of Nd1-xCaxBa2Cu3Oy and Nd1-xLaxBa2Cu3Oy
- 2000
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In: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 339:4, s. 245-252
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Journal article (peer-reviewed)abstract
- The structural and transport properties of Nd1-xCaxBa2Cu3Oy (x = 0.0, 0.03, 0.06, and 0.10) and Nd1-xLax- Ba2Cu3Oy. (x nominally 0.0, 0.05, 0.10, and 0.15) have been studied by X-ray powder diffraction, electrical resistivity, and thermoelectric power measurements. In both series, the a- and b-axis lattice parameters decrease with increasing doping while the c-axis lattice parameter increases. The transport properties suggest improved metallic behaviour with increasing Ca doping in contrast to La doping. An anomalous sharp peak in the thermoelectric power close to T-c was observed, which depended on the doping content. We analysed the thermoelectric power as a function of temperature with a two-band model with an additional linear T term. An excellent agreement between model and data was obtained.
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| 3. |
- Ghorbani, Shaban Reza, et al.
(author)
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Thermoelectric power and resistivity of Nd1-xPrxBa2Cu3O7-delta
- 2001
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In: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 353:1-2, s. 77-84
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Journal article (peer-reviewed)abstract
- The structural and transport properties of Nd1-xPrxBa2Cu3O7-delta (x = 0.0, 0.05, 0.10, and 0.15), have been studied by X-ray powder diffraction, electrical resistivity measurements, and thermoelectric power measurements. The decrease of the superconducting critical temperature with doping is described by a parabolic term and a linear term. The c-axis lattice parameter and the cell volume decrease with doping up to x = 0.10. Analyses of the thermoelectric power, critical temperature, c-axis lattice parameter, and the cell volume suggest that the Pr ions have a valence close to +4 at low doping concentration. The room temperature resistivity indicates that hole concentration decreases with increasing Pr doping. The room temperature thermoelectric power is positive for all samples and increases with increasing Pr doping due to a decrease in the carrier concentration. We analyzed the thermoelectric power as a function of temperature with a two-band model with an additional linear T term. An excellent agreement between model and data was obtained. The band width of the narrow band increases and its peak position moves away from the Fermi energy with increasing doping concentration.
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| 4. |
- Siribbal, Shifaa M., et al.
(author)
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Air-Stable Gadolinium Precursors for the Facile Microwave-Assisted Synthesis of Gd2O3 Nanocontrast Agents for Magnetic Resonance Imaging
- 2018
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In: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 18:2, s. 633-641
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Journal article (peer-reviewed)abstract
- Using metal organic precursors in materials synthesis remains a challenge due to their high moisture susceptibility. In this work, we describe a facile methodology for the synthesis of Gd2O3-based contrast agents from two new gadolinium-based complexes. [Gd(PyTFP)(4)] (PyH) 1 (PyTFP = C8H5NOF3, Py = C5H5N) and [Gd(DMOTFP)(3)Py] 2 (DMOTFP = C8H7NO2F3) were synthesized via a classical ligand exchange reaction of [Gd{N(SiMe3)(2)}(3)] under inert conditions. As a result, X-ray diffraction analysis revealed a distorted square antiprismatic coordination and an augmented triangular prismatic arrangement of ligands around gadolinium atoms in 1 and 2, respectively. It also showed that 1 is an anionic complex of formula [Gd(PyTFP)(4)](PyH), while a neutral tris-compound, [Gd(DMOTFP)(3)Py], was obtained as a pyridine adduct in 2. Fast and reproducible microwave-assisted decomposition of 1 and 2 provided homogeneous Gd(OH)(3) nanorods at mild temperature without using any surfactant or capping reagent. As-synthesized nanorods were easily transformed into a cubic phase of Gd2O3 nanoparticles by thermal treatment under ambient conditions. The magnetic measurement showed the typical paramagnetic behavior of the Gd2O3 nanoparticles (NPs). The cytotoxicity profile demonstrates the biocompatibility and negligible toxicity of the as-synthesized nanoprobes. The suggested approach provides a new class of gadolinium-based precursors which allows facile synthesis of highly crystalline Gd2O3 NPs.
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| 5. |
- Valldor, M., et al.
(author)
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Preparation and characterisation of the double perovskite Sr2TaMnO6
- 2006
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In: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 299:1, s. 161-169
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Journal article (peer-reviewed)abstract
- The presented compound, Sr2TaMnO6, has a weak, disordered magnetic structure. The metal oxide was prepared under high isostatic oxygen pressure. The doubling of the perovskite structure was proven with electron diffraction and powder neutron diffraction. Combining neutron- and X-ray diffraction data, the room-temperature structure was modelled with the Rietveld method. Both octahedral positions are partially occupied by Mn and Ta, but with different Mn/Ta ratios. AC- and DC-magnetic measurements indicate a magnetic transition at about 17 K and the AC-magnetic susceptibility, both real and imaginary part, is frequency dependent, suggesting that the material has a spin-glass feature. The magnetic spins freeze during a wide temperature range and a possible explanation is a competative situation between the double exchange (ferromagnetism) and the super-exchange (anti-ferromagnetism).
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| 6. |
- Valldor, M., et al.
(author)
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The structure of the new compound YBaCo4O7 with a magnetic feature
- 2002
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In: Solid State Sciences. - 1293-2558 .- 1873-3085. ; 4:7, s. 923-931
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Journal article (peer-reviewed)abstract
- Single crystals and pure powder samples of the new compound YBaCo4O7 have been obtained by solid-state reactions, using different temperature programs. From X-ray powder diffraction the structure was determined as hexagonal, space group P6(3)mc. having the cell parameters a = 6.2982(4) and c = 10.2467(9) Angstrom. This phase is isostructural with that previously reported for LuBaZn3.09Al0.91O7. Refinements of powder neutron diffraction data collected at two different temperatures and X-ray single crystal data at room temperature, agree well. Changes with temperature in the relative positions of Co and its surrounding oxygen atoms are the only geometrical manifestation of a probable spin-glass transition at about 65 K from the high temperature paramagnetic state.
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| 7. |
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