We measured the density of vibrational states (DOS) and the specific heat of various glassy and crystalline polymorphs of SiO2. The typical (ambient) glass shows a well-known excess of specific heat ...relative to the typical crystal (α-quartz). This, however, holds when comparing a lower-density glass to a higher-density crystal. For glassy and crystalline polymorphs with matched densities, the DOS of the glass appears as the smoothed counterpart of the DOS of the corresponding crystal; it reveals the same number of the excess states relative to the Debye model, the same number of all states in the low-energy region, and it provides the same specific heat. This shows that glasses have higher specific heat than crystals not due to disorder, but because the typical glass has lower density than the typical crystal.
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► MBE deposition at room temperature and subsequent annealing for phase formation. ► This growth procedure easily yielded stoichiometric Sb2Te3 and Bi2Te3 thin films. ► Sb2Te3 films ...revealed favorable charge carrier density and mobility. ► Advanced characterization of texture by high-energy X-ray diffraction. ► Precise chemical analysis by calibrated EDX spectroscopy and energy-filtered TEM.
Sb2Te3 and Bi2Te3 thin films were grown at room temperature on SiO2 and BaF2 substrates using molecular beam epitaxy. A layer-by-layer growth was achieved such that metallic layers of the elements with 0.2nm thickness were deposited. The layer structure in the as-deposited films was confirmed by X-ray diffraction and was seen more clearly in Sb2Te3 thin films. Subsequent annealing was done at 250°C for 2h and produced the Sb2Te3 and Bi2Te3 crystal structure as confirmed by high-energy X-ray diffraction. This preparation process is referred to as nano-alloying and it was demonstrated to yield single-phase thin films of these compounds. In the thin films a significant texture could be identified with the crystal c axis being almost parallel to the growth direction for Sb2Te3 and tilted by about 30° for Bi2Te3 thin films. In-plane transport properties were measured for the annealed films at room temperature. Both films yielded a charge carrier density of about 2.6×1019cm−3. The Sb2Te3 films were p-type, had a thermopower of +130μVK−1, and surprisingly high mobilities of 402cm2V−1s−1. The Bi2Te3 films were n-type, showed a thermopower of −153μVK−1, and yielded significantly smaller mobilities of 80cm2V−1s−1. The chemical composition and microstructure of the films were investigated by transmission electron microscopy (TEM) on cross sections of the thin films. The grain sizes were about 500nm for the Sb2Te3 and 250nm for the Bi2Te3 films. In the Bi2Te3 thin film, energy-filtered TEM allowed to image a Bi-rich grain boundary phase, several nanometers thick. This secondary phase explains the poor mobilities of the Bi2Te3 thin film. With these results the high potential of the nano-alloying deposition technique for growing films with a more complex layer architecture is demonstrated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
To calculate the thermodynamic properties of recently discovered high-pressure mixed valence iron oxides in the system Fe–Mg–O, information on the equation of state of precursor inverse spinel phases ...along the magnetite–magnesioferrite join is needed. The existing equation of state data, particularly for magnesioferrite, are in poor agreement and no data exist for intermediate compositions. In this study, the compressibility of nearly pure magnesioferrite as well as of an intermediate
Mg
0.5
Fe
0.5
2
+
Fe
2
3
+
O
4
sample have been investigated for the first time up to approximately 19 and 13 GPa, respectively, using single-crystal X-ray diffraction in a diamond anvil cell. Samples were produced in high-pressure synthesis experiments to promote a high level of cation ordering, with the obtained inversion parameters larger than 0.83. The room pressure unit cell volumes,
V
0
, and bulk moduli,
K
T
0
, could be adequately constrained using a second-order Birch–Murnaghan equation of state, which yields
V
0
= 588.97 (8) Å
3
and
K
T
0
= 178.4 (5) GPa for magnesioferrite and
V
0
= 590.21 (5) Å
3
and
K
T
0
= 188.0 (6) GPa for the intermediate composition. As magnetite has
K
T
0
= 180 (1) GPa (Gatta et al. in Phys Chem Min 34:627–635, 2007.
https://doi.org/10.1007/s00269-007-0177-3
), this means the variation in
K
T
0
across the magnetite–magnesioferrite solid solution is significantly non-linear, in contrast to several other Fe–Mg spinels. The larger incompressibility of the intermediate composition compared to the two end-members may be a peculiarity of the magnetite–magnesioferrite solid solution caused by an interruption of Fe
2+
–Fe
3+
electron hopping by Mg cations substituting in the octahedral site.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The lattice dynamics of polycrystalline Mg2Ge and Mg2Si are compared using both microscopic and macroscopic measurements as well as theoretical calculations. The volume thermal expansion coefficient ...between 200 and 300 K was found to be 4.37(5) · 10−5 K−1 in Mg2Ge, compared to 3.69(5) · 10−5 K−1 in Mg2Si. Inelastic neutron scattering measurements yield densities of phonon states which are in line with theoretical calculations. The microscopic data were corroborated with macroscopic calorimetry measurements and provide quantified values for anharmonicity. The estimated macroscopic Grüneisen parameter is, γMg2Si = 1.17(5) and γMg2Ge = 1.46(5) at 295 K, in excellent agreement with Raman scattering data. Although the element specific mean force constants are practically the same, in Mg2Ge and Mg2Si, a mass homology relation alone cannot reproduce the difference in the partial densities of vibrational states in these compounds and differences in elemental bonding should be taken into account.
The assembly of a Lock-In digital Amplifier (LIdA) from widely accessible ready-made modules is presented. This equipment, which does not require any advanced knowledge of electronics or programming, ...may introduce the experimenter to resonant techniques by registering mechanical resonances. The freely available control program allows for general data acquisition and further data processing. The apparatus is versatile and may corroborate the science and engineering laboratory in elasticity measurements or in a series of experiments where a modulated signal is a prerequisite.
Mössbauer reflectivity spectra measured for the Fe(3.0 nm)/Cr(1.2 nm)
10
structure in the half-order Bragg peak, which corresponds to the doubling of the period, have revealed the formation of a ...canted antiferromagnetic structure under the action of an external magnetic field of
Т applied perpendicular to the scattering plane. This result certainly follows from the appearance of the second and fifth lines in the Mössbauer sextet, which should be suppressed for any symmetric orientation of the magnetic hyperfine field in two
57
Fe layers in one magnetic period. The experiment involves a polarization analysis of the reflected beam and shows that this new approach simplifies the form of angular dependences and reflectivity spectra, since it eliminates the interfering contribution of nonresonant scattering, and improves the reliability of the data interpretation.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
To design custom magnetic nanostructures, it is indispensable to acquire precise knowledge about the systems in the nanoscale range where the magnetism forms. In this paper we present the effect of a ...curved surface on the evolution of magnetism in ultrathin iron films. Nominally 70 Å thick iron films were deposited in 9 steps on 3 different types of templates: (a) a monolayer of silica spheres with 25 nm diameter, (b) a monolayer of silica spheres with 400 nm diameter and (c) for comparison a flat silicon substrate.
In situ
iron evaporation took place in an ultrahigh vacuum chamber using the molecular beam epitaxy technique. After the evaporation steps, time differential nuclear forward scattering spectra, grazing incidence small angle X-ray scattering images and X-ray reflectivity curves were recorded. In order to reconstruct and visualize the magnetic moment configuration in the iron cap formed on top of the silica spheres, micromagnetic simulations were performed for all iron thicknesses. We found a great influence of the template topography on the onset of magnetism and on the developed magnetic nanostructure. We observed an individual magnetic behaviour for the 400 nm spheres which was modelled by vortex formation and a collective magnetic structure for the 25 nm spheres where magnetic domains spread over several particles. Depth selective nuclear forward scattering measurements showed that the formation of magnetism begins at the top region of the 400 nm spheres in contrast to the 25 nm particles where the magnetism first appears in the region where the spheres are in contact with each other.
The role of nanoparticle size, interparticle distance and magnetic layer thickness on the formation of magnetic nanostructures was studied. Individual magnetic behaviour was found for the 400 nm spheres and a collective magnetic structure for the 25 nm balls where magnetic domains spread over several particles.
Bulk Sr2PdO3 was synthesized by a modified solid state reaction and a detailed characterization was carried out using both microscopic and macroscopic experimental techniques. Pd site exhibits an ...electric field gradient of 5.9(1) ⋅ 1017 V/cm2 due to the anisotropic local atomic configuration. A Curie - paramagnetic susceptibility indicating antiferromagnetic interactions superimposed to a core diamagnetic state is confirmed. A linear volume thermal expansion with a coefficient of 3.0(1) ⋅ 10−5 K−1 at room temperature is extracted. A collection of Einstein oscillators, with an Einstein temperature of about 115 K, is involved in the thermal transport. Large atomic displacements were observed in Sr vibrations. No Pd or Sr valence change is observed up to 900 K. A moderate anharmonicity is identified and quantified in a macroscopic Grüneisen parameter of 2.5(1) at room temperature. The electrical resistivity reveals a semiconducting behaviour. A systematic reduction in electrical resistivity and a change in the conduction mechanism is observed upon thermal cycling which indicates that a peculiar electronic mechanism is involved.
•A combined microscopic and macroscopic experimental characterization of bulk Sr2PdO3 is carried out in this study.•A collection of Einstein oscillators impedes thermal transport.•A systematic reduction in electrical resistivity and a change in the conduction mechanism is observed upon thermal cycling.•The estimated Einstein temperature coincides with the activation energy of the electronic transport.•The change in the conduction mechanism is likely to be related to oxygen delocalization from the apical sites to PdO4 conduction planes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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