855 research outputs found
Polaron Effects on Superexchange Interaction: Isotope Shifts of , , and in Layered Copper Oxides
A compact expression has been obtained for the superexchange coupling of
magnetic ions via intermediate anions with regard to polaron effects at both
magnetic ions and intermediate anions. This expression is used to analyze the
main features of the behavior of isotope shifts for temperatures of three types
in layered cuprates: the Neel temperatures (), critical temperatures of
transitions to a superconducting state (), and characteristic temperatures
of the pseudogap in the normal state ().Comment: 4 pages, 1 figur
Determination of glass transition temperature for polymers by methods of thermoactivation spectroscopy
For rapid determination of glass transition temperature for polymers, we propose a method of thermally stimulated luminescence. The experiments were carried for epoxy polymers dyed and undyed with organic dyes. It is shown that glass transition temperature depends on curing temperature and concentration of the dye. The comparison with the thermogravimetric analysis showed coincidence of the results obtained
Pressure-induced electronic phase separation of magnetism and superconductivity in CrAs
The recent discovery of pressure induced superconductivity in the binary
helimagnet CrAs has attracted much attention. How superconductivity emerges
from the magnetic state and what is the mechanism of the superconducting
pairing are two important issues which need to be resolved. In the present
work, the suppression of magnetism and the occurrence of superconductivity in
CrAs as a function of pressure () were studied by means of muon spin
rotation. The magnetism remains bulk up to ~kbar while its volume
fraction gradually decreases with increasing pressure until it vanishes at
7~kbar. At 3.5 kbar superconductivity abruptly appears with its
maximum ~K which decreases upon increasing the pressure. In the
intermediate pressure region (~kbar) the
superconducting and the magnetic volume fractions are spatially phase separated
and compete for phase volume. Our results indicate that the less conductive
magnetic phase provides additional carriers (doping) to the superconducting
parts of the CrAs sample thus leading to an increase of the transition
temperature () and of the superfluid density (). A scaling of
with as well as the phase separation between magnetism and
superconductivity point to a conventional mechanism of the Cooper-pairing in
CrAs.Comment: 9 pages, 8 figure
Effect of ion irradiation on the surface energy of deposited coatings
We investigated multi-element coatings exposed to argon ion bombardment. The coatings were irradiated using a multi-ampere hollow-cathode ion source. The arc current was 1 A, and the potential of the substrate was maintained equal to 300 V. The surface tension (surface energy) of the coatings was measured before and after irradiation through the size-dependence of the microhardness and electrical resistivity of coatings on their thickness. Ion irradiation was found to affect the surface energy of the coatings in different ways. This is due to both the structure of the coating and its elemental composition
Effect of ion irradiation on the properties multi-element plasma coatings
The paper presents the results of the study of ion irradiation on the properties of multi-element plasma coatings. The coatings were bombarded by argon ions using heavy current ion source with a hollow cathode. After ion irradiation, the structure and physical properties of the coatings change, however, the nature of the changes is different for different coatings. To predict the behavior of the coating exposed to irradiation is virtually impossible. Therefore, structural studies and investigation of physical properties of the coatings to determine their functional characteristics are to be conducted
Effect of ultraviolet and x-ray radiation on optical properties of epoxy polymers dyed with organic phosphors
Highly purified industrial bisphenol and cycloaliphatic epoxy oligomers of ED-24 and UP-612 brands were used to produce optically transparent products. UV radiation of a low-pressure mercury lamp with 80% of the light energy at 254 nm was used to study photodegradation. X-ray apparatus with 0.7BSV- Ag tube was used as an ionizing radiation source to investigate the effect of X-rays on the spectra of organic dyes in epoxy polymer. The threshold value of the energy generated by ruby laser which indicated the degradation in the test samples recorded by light scattering method was determined to study radiation resistance of epoxy polymers. Basically, all the dyes exhibited high resistance to UV light. The observation of the absorption spectra showed that on average, a third of the dye molecules in the matrix experienced photobleaching within 200 hour exposure. The exception was coumarin 1, which was completely decolourized after 40 hours of exposure. X-ray irradiation of the samples for two hours results in the change in the optical density equivalent to that caused by 40 hour exposure to UV irradiation. However, in the first case, the matrix optical density is proportional to the irradiation time, and in the second case, it remains stable upon further UV irradiation. The comparison of photoaging processes in dyed and undyed epoxy polymers showed that the investigated organic dyes do not have a sensitizing effect on the matrix. The stability of the optical properties of the epoxy matrices exposed to the effects of different factors was found to depend on the nature of epoxy polymer and the technique of its production. The results of these effects are significantly different in the character of the change in the optical density and mechanisms of chemical transformations in polymer
Thermodynamic models of radiation-induced processes in solids
A thermodynamic model is proposed to qualitatively describe the radiation-induced processes in solids: temperature dependence of the X-ray radio luminescence output, dependence of these processes on the excitation density, energy accumulating in a solid under exposure to ionizing radiation and its temperature dependence. The proposed model and the formula derived can be used to develop radiation-resistant and radiation-sensitive materials
- β¦