Currently, special attention is paid to the search for new ceramic materials based on wide-gap oxides, as well as to the study of their structure and properties with a view to their application in ...various areas of electronic and optoelectronic industry.
Conventional double-step ceramic technology has been used to obtain samples in this experiment. After compacting at the pressure of 6 GPa of ZnO and ZnO-FexOy powders in different weight relations, the samples were subjected to the procedure of synthesis at 1173 K for 2 h and then to the annealing at 1473 K for 3 h on air.
The samples structure was investigated by the Scanning Electron Microscopy (SEM), Energy-dispersive X-ray Spectroscopy (EDX), X-ray Diffraction (XRD) and Raman spectroscopy methods. Temperature dependences of resistivity, magnetoresistance, Hall and Seebeck effects were experimentally studied in the range from 4 to 700 K.
As the experiments have shown, the size of grains in the obtained ceramic samples after synthesis was in submicron range. An XRD study showed the saving of the wurtzite structure in Zn1-δFeδO solid solutions where 0.66 < δ < 0.81 at. % regardless of the type of the doping agent. At the same time, the replacement of zinc by iron atoms led to the contraction of the ZnO lattice.
All the samples studied (ZnO and Zn1-δFeδO) demonstrate n-type conductivity. The temperature dependencies of resistivity have shown two specific features: the presence of energy level about 0.35 eV below the conduction band bottom for the doped ceramic samples (unknown in literature) and conductance with the changing activation energy at temperatures below 200 K for the undoped ZnO ceramic samples. Seebeck coefficient increased by100–150% with doping due to growth of electron concentration. Some model concepts about scattering mechanisms and reasons of Seebeck effect enhancement have been developed.
•Ceramic materials based on wide-gap oxides.•Investigation by SEM, EDX, XRD and Raman spectroscopy methods.•Size of grains in the obtained ceramic samples after synthesis was in submicron range.•Saving of the wurtzite structure in Zn1-δFeδO solid solutions.•Studied samples (ZnO and Zn1-δFeδO) demonstrate n-type conductivity.
The purpose of the research is to evaluate the operational and ecological parameters of an engine fed by various types of fuel. The test stand constructed for this purpose was prepared to evaluate ...the engine work indicators for eight different types of motor gasolines from different manufacturers and with different octane number. The tests were performed on a Fiat 170A1 engine. Parameters that were measured directly in the test were: rotational speed, torque, fuel consumption, exhaust gas temperature, run of indicated pressure. The conducted research and comparative analysis of the obtained results confirmed that the type of fuel used does not significantly affect the obtained values of ecological and operating parameters. The higher fuel octane number with the compression ratio used in the research engine did not affect the higher values of the measured parameters.
The analysis of 57Fe Mössbauer spectroscopy results for cation and anion substituted Mn2-xFexP1-yAsy was done in order to find out the influence of the Mn/Fe ratio on the magnetic properties of solid ...solutions and to compare experimental hyperfine parameters with those calculated from firstprinciples.The correlation between third Mössbauer sextet in Mn2-xFexP0.5As0.5 spectrum at 77K and stabilization of the antiferromagnetic phase for x = 0.5-0.6 was found on the basis of comparison between the magnetic phase diagrams and the "hyperfine field - iron content" dependence. The observed qualitative difference for Mn2-xFexP0.5As0.5 and MnFeAsyP1-y "hyperfine field - concentration" diagrams was interpreted on the basis of different mechanisms of magnetic phase stabilization and the different configurations of tetrahedral anionic environment of iron ions for systems with cation and anion substitutions.
We present a new catalogue of 55 121 groups and clusters centred on luminous red galaxies from Sloan Digital Sky Survey Data Release 7 in the redshift range 0.15 ≤z≤ 0.4. We provide halo mass (M
500) ...estimates for each of these groups derived from a calibration between the optical richness of bright galaxies (M
r
≤−20.5) within 1 Mpc and X-ray-derived mass for a small subset of 129 groups and clusters with X-ray measurements. For 20 157 high-mass groups and clusters with M
500 > 1013.7 M⊙, we find that the catalogue has a purity of >97 per cent and a completeness of ∼90 per cent. We derive the mean (stacked) surface number density profiles of galaxies as a function of total halo mass in different mass bins. We find that derived profiles can be well described by a projected Navarro-Frenk-White profile with a concentration parameter (〈c〉≡〈r
200/r
s〉≈ 2.6) that is approximately a factor of 2 lower than that of the dark matter (as predicted by N-body cosmological simulations) and nearly independent of halo mass. Interestingly, in spite of the difference in shape between the galaxy and dark matter radial distributions, both exhibit a high degree of self-similarity. We also stack the satellite profiles based on other observables, namely redshift, brightest cluster galaxy (BCG) luminosity and satellite luminosity and colour. We see no evidence for strong variation in profile shape with redshift over the range we probe or with BCG luminosity (or BCG luminosity fraction), but we do find a strong dependence on satellite luminosity and colours, in agreement with previous studies. A self-consistent comparison to several recent semi-analytic models of galaxy formation indicates that (1) beyond ≈0.3r
500 current models are able to reproduce both the shape and normalization of the satellite profiles, and (2) within ≈0.3r
500 the predicted profiles are sensitive to the details of the satellite-BCG merger time-scale calculation. The former is a direct result of the models being tuned to match the global galaxy luminosity function combined with the assumption that the satellite galaxies do not suffer significant tidal stripping, even though their surrounding dark matter haloes can be removed through this process. Combining our results with measurements of the intracluster light should provide a way to inform theoretical models on the efficacy of the tidal stripping and merging processes.
We have examined the influence of external magnetic fields up to
H
= 14 T on the phase transitions of MnAs, MnAs
0.99
P
0.01
, and MnAs
0.98
P
0.02
single crystals. The results indicate that there is ...structural instability of the crystal lattice, associated with anomalous compression at temperatures from
≃ 250 K to the phase transition temperature
T
u
and anomalous lattice expansion in the basal plane between
T
u
and
≃ 350 K. Near the first-order phase transition, the magnetic entropy change at a magnetic field change from 0 to 14 T is about 40 J/(kg K) in single-crystal MnAs and approaches 50 J/(kg K) in single-crystal MnAs
0.98
P
0.02
.
((Fe0.9Co0.1)Ox/MCM-41 nanocomposite material was prepared by wet impregnation of the silica mesoporous template with iron and cobalt mixture of aqueous salt solutions. The phase analysis of the ...obtained samples carried out by X-ray diffraction method and studies of magnetic properties using 57Fe Mössbauer spectroscopy revealed the presence of nanostructured magnetite- and maghemite-like phases. The transformation to bimetallic Fe0.9Co0.1 and fayalite phases accompanied the reduction process in hydrogen at 1073 K. The contribution of ferrimagnetic phases in relation to superparamagnetic phases increases when temperature changes from 295 K to 13K in the sample before reduction what is characteristic for nanoparticles.
We employ a large sample of 20 171 optically selected groups and clusters at 0.15 ≤ z ≤ 0.4 in the Sloan Digital Sky Survey to investigate how the stacked stellar mass fraction varies across a wide ...range of total mass, M
500. Our study improves upon previous observational studies in a number of important ways, including having a much larger sample size, an explicit inclusion of the intracluster light (ICL) component and a thorough examination of the accuracy of our total mass estimates via comparisons to simulations and weak lensing observations. We find that the stellar mass fraction depends only weakly on total mass and that the contribution of ICL to the total stellar mass fraction is significant (typically 20-40 per cent). Both of these findings are in excellent accordance with the predictions of cosmological simulations. Under the assumption of a Chabrier (Salpeter) initial mass function, the derived star formation efficiency (f
star/f
b, where f
b ≡ Ωb/Ωm) is relatively low at 8 per cent (14 per cent) and is consistent with the global star formation efficiency of semi-analytic models that reproduce the galaxy stellar mass function. When our measured stellar mass fractions are combined with the observed relation between the hot gas mass fraction and total mass from X-ray observations, our results imply that galaxy groups have significantly lower baryon fractions than massive clusters. Ejection of gas due to energetic AGN feedback (most likely at high redshift) provides a plausible mechanism for explaining the trends we observe.
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