1,721,957 research outputs found
Electronic mobility and crystal structures of 2,5-dimethylanilinium triiodide and tin-based organic-inorganic hybrid compounds
Full text linkWe synthesize single crystals of a new 2,5-dimethylanilinium tin iodide organic-inorganic hybrid compound and 2,5-dimethylanilinium triiodide. Single-crystal X-ray diffraction reveals that the hybrid grows as a unique rhombohedral structure consisting of one-dimensional chains of SnI6-octahedra that share corners and edges to build up a ribbon along the [111] direction. Notably, we find that hypophosphorous acid, H3PO2, is of central importance to the formation of this hybrid. In the absence of H3PO2, we synthesize 2,5-dimethylanilinium triiodide from the same starting compounds. We investigate the synthesis routes that drive the growth of these two compounds with distinct crystal structures, appearance and properties. Pulse-radiolysis time-resolved microwave conductivity measurements and density functional theory calculations reveal that both compounds have low charge carrier mobilities and very long lifetimes, consistent with their one-dimensional structural characteristics. Our findings give a better understanding of the relation between synthesis, crystal structures and charge carrier mobilities.ChemE/Opto-electronic Material
Phase diagram and magnetic relaxation phenomena in Cu2OSeO3
Full text linkWe present an investigation of the magnetic-field-temperature phase diagram of Cu2OSeO3 based on dc magnetization and ac susceptibility measurements covering a broad frequency range of four orders of magnitude, from very low frequencies reaching 0.1 Hz up to 1 kHz. The experiments were performed in the vicinity of Tc=58.2 K and around the skyrmion lattice A phase. At the borders between the different phases the characteristic relaxation times reach several milliseconds and the relaxation is nonexponential. Consequently the borders between the different phases depend on the specific criteria and frequency used and an unambiguous determination is not possible.</p
Magnetic phase diagram and cluster glasslike properties of stage-1 graphite-intercalated FeCl3
Full text linkWe present a comprehensive investigation of the magnetic properties of stage-1 graphite intercalated FeCl3 using a combination of DC and AC magnetic susceptibility, thermoremanent magnetization, and field-dependent magnetization measurements. This van der Waals system, with a centrosymmetric honeycomb lattice, combines frustration and disorder, due to intercalation, and may be hosting topologically nontrivial magnetic phases. Our study identifies two magnetic phase transitions at Tf1≈4.2 K and at Tf2≈2.7 K. We find that the paramagnetic state, for T>Tf1, is dominated by short-range ferromagnetic correlations. These build up well above Tf1 and lead to a significant change in magnetic entropy, which reaches ΔSMPk=-5.52 J kg-1K-1 at 7 T. Between Tf1 and Tf2, we observe slow spin dynamics characteristic of a cluster glasslike state, whereas for T<Tf2, our results indicate the onset of a low-temperature long-range ordered state. The analysis of the experimental results leads to a complex phase diagram, which may serve as a reference for future investigations searching for topological nontrivial phases in this system. RST/Neutron and Positron Methods in Material
Phase Transitions of Thermoelectric TAGS-85
Full text linkThe alloys (GeTe)x(AgSbTe2)100-x, commonly known as TAGS-x, are among the best performing p-type thermoelectric materials for the composition range 80 ≤ x ≤ 90 and in the temperature range 200-500 °C. They adopt a rhombohedrally distorted rocksalt structure at room temperature and are reported to undergo a reversible phase transition to a cubic structure at ∼250 °C. However, we show that, for the optimal x = 85 composition (TAGS-85), both the structural and thermoelectric properties are highly sensitive to the initial synthesis method employed. Single-phase rhombohedral samples exhibit the best thermoelectric properties but can only be obtained after an annealing step at 600 °C during initial cooling from the melt. Under faster cooling conditions, the samples obtained are inhomogeneous, containing multiple rhombohedral phases with a range of lattice parameters and exhibiting inferior thermoelectric properties. We also find that when the room-temperature rhombohedral phase is heated, an intermediate trigonal structure containing ordered cation vacancy layers is formed at ∼200 °C, driven by the spontaneous precipitation of argyrodite-type Ag8GeTe6 which alters the stoichiometry of the TAGS-85 matrix. The rhombohedral and trigonal phases of TAGS-85 coexist up to 380 °C, above which a single cubic phase is obtained and the Ag8GeTe6 precipitates redissolve into the matrix. On subsequent cooling a mixture of rhombohedral, trigonal, and Ag8GeTe6 phases is again obtained. Initially single-phase samples exhibit thermoelectric power factors of up to 0.0035 W m-1 K-2 at 500 °C, a value that is maintained on subsequent thermal cycling and which represents the highest power factor yet reported for undoped TAGS-85. Therefore, control over the structural homogeneity of TAGS-85 as demonstrated here is essential in order to optimize the thermoelectric performance.RST/Neutron and Positron Methods in Material
The role of the hydrogen bonding network for the shear modulus of PIPD
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Magnetic field dependent cycloidal rotation in pristine and Ge-doped CoCr2O4
Full text linkWe report a soft x-ray resonant magnetic scattering study of the spin configuration in multiferroic thin films of Co0.975Ge0.025Cr2O4 (Ge-CCO) and CoCr2O4 (CCO) under low and high magnetic fields from 0.2 to 6.5 T. A characterization of Ge-CCO at a low magnetic field was performed, and the results were compared with those of pure CCO. The ferrimagnetic phase transition temperature T-C approximate to 95 K and the multiferroic transition temperature T-S approximate to 27 K in Ge-CCO are comparable with those observed in CCO. In Ge-CCO, the ordering wave vector (qq0) observed below T-S is slightly larger compared with that of CCO, and unlike CCO, the diffraction intensity consists of two contributions that show a dissimilar x-ray polarization dependence. In Ge-CCO, the coercive field observed at low temperatures was larger than the one reported for CCO. In both compounds, an unexpected reversal of the spiral helicity, and therefore the electric polarization, was observed on simply magnetic field cooling. In addition, we find a change in the helicity as a function of momentum transfer in the magnetic diffraction peak of Ge-CCO, indicative of the presence of multiple magnetic spirals.</p
Cation distribution and interatomic interactions in oxides with heterovalent isomorphism: X. Structure of the Ho2SrAl2O7 oxide at 100, 298, and 673 K
Full text linkCrystallochemical data for the Ho2SrAl2O7 oxide at 100, 293, and 6731 K were obtained by full-profile X-ray analysis. Analysis of the thermal expansion anisotropy showed that increased temperature gives rise to equalization of metal-oxygen bond lengths in all oxygen polyhedra at the expense of lengthening of' some bonds and virtual invariability of others
Organotin(IV) 4-nitrophenylethanoates: Synthesis, structural characteristics and intercalative mode of interaction with DNA
No full textFour new organotin(IV) carboxylates, [Bu(2)SnL(2)] (1), [Et(2)SnL(2)] (2), [Bu(3)SnL](n) (3), [Me(3)SnL](n) (4), where L = 4-nitrophenylethanoates, were synthesized and characterized by elemental analysis, FT-IR and multinuclear NMR ((1)H and (13)C). Spectroscopic results authenticated the coordination of ligand to the organotin moiety via COO group while X-ray single crystal analysis revealed bidentate chelating mode of coordination of ligand in complex 2 and a bridging behavior in complexes 3 and 4. Cyclic voltammetric ( CV) technique was used to evaluate the electrochemical, kinetic and thermodynamic parameters of complexes 1-4, interacting with DNA. The linearity of the plots between the peak current (I) and the square root of the scan rate (nu(1/2)) indicated the electrochemical processes to be diffusion controlled. The diffusion coefficients of the free (D(f)) and DNA bound forms (D(b)), standard rate constants (ks) and charge transfer coefficients (alpha) were determined by the application of Randle-Sevcik, Nicholson and Kochi equations. Furthermore, the binding constants evaluated from voltammetric data revealed the following increasing order of binding strength: 2 <1 <4 <3. For 1 and 2, the activity against prostate cancer cell lines (PC-3) was found consistent with the order obtained from voltammetric behavior. (C) 2009 Elsevier B.V. All rights reserved
A three-component reaction of phenol, aldehyde, and active methylene substrate under Lewis acid catalysis: Successful trapping of o-quinone methide to afford benzopyran systems
No full textA three-component condensation involving reactive phenols, aldehydes, and active methylene substrates is described under BF3.Et2O catalysis to afford benzopyranyl products in satisfactory yields
2 p-insulator heterointerfaces: Creation of half-metallicity and anionogenic ferromagnetism via double exchange
Full text linkWe use first-principles calculations to predict the occurrence of half-metallicity and anionogenic ferromagnetism at the heterointerface between two 2p insulators, taking the KO2/BaO2 (001) interface as an example. Whereas a sharp heterointerface is semiconducting, a heterointerface with a moderate concentration of swapped K and Ba atoms is half-metallic and ferromagnetic at ambient pressure due to the double exchange mechanism. The K-Ba swap renders the interfacial K-O and Ba-O atomic layers electron-doped and hole-doped, respectively. Our findings pave the way to realize metallicity and ferromagnetism at the interface between two 2p insulators, and such systems can constitute a new family of heterostructures with novel properties, expanding studies on heterointerfaces from 3d insulators to 2p insulators
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