Abstract
Measurements of the microwave surface impedance for high-temperature superconductor YBa
2
Cu
3
O
7−
x
(YBCO) films irradiated by 3 MeV Au
2+
ions at three irradiation doses (10
10
cm
−2
, 10
...11
cm
−2
, and 10
12
cm
−2
) were carried out at different temperatures (below the critical temperature of
T
с
≈ 90 К) and various rf current amplitudes by the use of the microstrip resonator technique. A noticeable decrease in the surface resistance and an enhancement of the linear response range at low temperatures were observed for moderately irradiated film exposed to an irradiation dose of 10
11
cm
−2
, while at higher irradiation doses (10
12
cm
−2
) an increase in the surface resistance and a decrease in the linear response range were observed for all temperatures below
T
c
. These results are discussed in the framework of phenomenological theory for the microwave response of superconductors with nano-sized structural defects.
In the paper, results of variations of structure, oxidation resistance, and electrical conductivity of novel MAX-phase composite coating are presented. The characteristics of highly dense Ti-Al-C ...composite bulks and vacuum-arc deposited 6 μm thick coatings before and after heating at 600 °C in air for 1000 h were compared. High electrical conductivity (σ = 1.3·106 S/m) of the highly resistant toward oxidation (Δm/S = 0.07 mg/cm2) Ti-Al-C coating was preserved after long-term heating in air. It was found that the specimen surface layers of MAX-phases Ti3AlC2 and Ti2AlC based bulks and chromium-containing Crofer 22APU steel became semiconductors because of high-temperature long-term oxidation (at 600 °C). The vacuum-arc deposited Ti-Al-C composite coating revealed high oxidation resistance and electrical conductivity along with good mechanical characteristics, namely nanohardness H(10mN) = 9.5 ± 1.5 GPa, and Young’s modulus E = 190 ± 10 GPa, which make it very promising for interconnects of solid oxide fuel cells (SOFCs).
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The oxygen concentration and distribution in the microstructure of MgB 2 - and YBa 2 Cu 3 O 7-δ -based materials affect the formation of nanostructural defects and thus influence the critical current ...density, upper critical magnetic field and irreversibility field. For MgB 2 oxygen containing additions (Dy-O, Ti-O) in the form of nanograins occurred not to be very effective for an increase of critical current density, j c . Sn-O additions to MgB 2 can provoke even a significant decrease of j c due to a chemical interaction of Sn with MgB 2 . The processing pressure and temperature influence the defect density of the relevant pinning centers and the regularity of their distribution in doped and undoped MgB 2 as well as in MT-YBCO.
Comprehensive experimental results of fully oxidized (up to YBa2Cu3O6,9-7) melt-textured YBaCuO materials with different microstructures are presented. These microstructures are built respectively: ...(1) with a high dislocations density but almost without twins (after high temperature treatment at 2 GPa) and (2) with a high twin density, but practically free from dislocations and stacking faults (after high temperature oxygenation at 10-16 MPa). It is shown that for attaining high critical current densities and fields of irreversibility (jc(H||c, 0 T)=9·104 A/cm2, Hirr=9.7 T at 77 K), a high twin density in YBa2Cu3O6.9-7 matrix of MT-YBCO is required. The density of twins in fully oxidized materials depends on the distances between Y2BaCuO5 inclusions, larger twin densities are related to shorter distances between inclusions. The influence of phase composition of the initial powder mixtures on the distances between Y2BaCuO5 inclusions have been characterized and discussed.
The correlations between structures and mechanical characteristics of α-AlB12-, AlB12C2-, B4C-based lightweight ceramics and composites synthesized or sintered by hot pressing (at 30 MPa) and ...SiC-based ceramics obtained by reactive sintering are compared. The effect of C, TiC and SiC additions on the properties of the resultant composites and the particularities of the ceramics destruction under shock loading are discussed. Ballistic tests performed on 10 mm thick plates fabricated from the developed ceramics (2.63 g/cm3 density; 78 wt% B4C and 22 wt% SiC composition according to X-ray diffraction analysis; B3.64CSi0.01 and SiC1.07 stoichiometry according to SEM microprobe X-ray analysis), showed that the material could withstand a 10 m distance shot using a bullet with initial kinetic energy of 3.7 kJ.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
8.
Charge and heat transfer of the Ti3AlC2 MAX phase Vovk, R. V.; Khadzhai, G. Ya; Prikhna, T. A. ...
Journal of materials science. Materials in electronics,
07/2018, Volume:
29, Issue:
13
Journal Article
Peer reviewed
Open access
The electrical and thermal conductivity of the sample containing 97% by volume of the Ti
3
AlC
2
MAX phase and 3% volume TiC was experimentally studied in the temperature range 15–300 K. The ...temperature dependence of the electrical resistance is approximated by a relation that takes into account the scattering of electrons by phonons and defects. The temperature dependence of the thermal conductivity shows a maximum at about 75 K. In the region of elastic scattering of electrons, the phonon and electron heat transfer are separated. With increasing temperature, the fraction of phonon heat transfer decreases from ∼90% at low temperatures to ∼40% near room temperature.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Regularly distributed structural inhomogeneities in the MgB2 matrix, such as nano-areas with a high concentration of boron (MgBx) and impurity oxygen (Mg-B-O nano-layers or inclusions), are observed ...in all materials independently of the preparation method, pressure (0.1 MPa-2 GPa) and temperature (600-1100 °C), and in materials with different connectivity (18-98%) and density (55-99%). Such inhomogeneities can act as pinning centers in MgB2 because the variation of their size and distribution are well correlated with variations of the critical current density, jc. The decrease in size of MgBx inclusions, the transformation of 15-20 nm thick Mg-B-O nano-layers into separated inclusions, and the localization of impurity oxygen are accompanied by an increase in critical current density in low and medium magnetic fields. The efficiency of these defects is evidenced by a shift from grain-boundary pinning to point pinning.
We prepared samples of composites based on tungsten carbide and cobalt with different concentrations (0–10 wt %) of chromium diboride, 10 mm in diameter and 8 mm in thickness, by cold pressing ...followed by vacuum hot pressing. A comprehensive study of composites using conventional methods of testing mechanical properties, combined with digital optical microscopy, transmission microscopy, and scanning atomic force microscopy, revealed stable correlations between the concentration of CrB
2
additive with the average WC grain size and microstructure parameters, hardness, and fracture toughness of the composites. A coarse-grained structure is observed in WC–6Co (wt %) composites, with direct contact of WC grains and large regions of a cobalt binder. The introduction of CrB
2
into the composite, on the contrary, ensures the formation of thin (~100 nm) and extended layers of a cobalt binder, even between fine WC grains. The CrB
2
additive yields a finer-grained structure, the parameters of which can be purposefully controlled by changing the additive concentration. The addition of 4 wt % of CrB
2
into the composite leads to a more than twofold increase in fracture toughness, that is, from 4.4 to 9.8 MPa m
1/2
, with a slight decrease in hardness from 15.1 to 13.0 GPa. With a further increase in the CrB
2
concentration from 4 to 10 wt %, fracture toughness and hardness gradually decrease.
Full text
Available for:
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
PDF
