A superconductor is a material that can conduct electricity without resistance below a superconducting transition temperature, Tc. The highest Tc that has been achieved to date is in the copper oxide ...system: 133 kelvin at ambient pressure and 164 kelvin at high pressures. As the nature of superconductivity in these materials is still not fully understood (they are not conventional superconductors), the prospects for achieving still higher transition temperatures by this route are not clear. In contrast, the Bardeen-Cooper-Schrieffer theory of conventional superconductivity gives a guide for achieving high Tc with no theoretical upper bound--all that is needed is a favourable combination of high-frequency phonons, strong electron-phonon coupling, and a high density of states. These conditions can in principle be fulfilled for metallic hydrogen and covalent compounds dominated by hydrogen, as hydrogen atoms provide the necessary high-frequency phonon modes as well as the strong electron-phonon coupling. Numerous calculations support this idea and have predicted transition temperatures in the range 50-235 kelvin for many hydrides, but only a moderate Tc of 17 kelvin has been observed experimentally. Here we investigate sulfur hydride, where a Tc of 80 kelvin has been predicted. We find that this system transforms to a metal at a pressure of approximately 90 gigapascals. On cooling, we see signatures of superconductivity: a sharp drop of the resistivity to zero and a decrease of the transition temperature with magnetic field, with magnetic susceptibility measurements confirming a Tc of 203 kelvin. Moreover, a pronounced isotope shift of Tc in sulfur deuteride is suggestive of an electron-phonon mechanism of superconductivity that is consistent with the Bardeen-Cooper-Schrieffer scenario. We argue that the phase responsible for high-Tc superconductivity in this system is likely to be H3S, formed from H2S by decomposition under pressure. These findings raise hope for the prospects for achieving room-temperature superconductivity in other hydrogen-based materials.
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Conductive dense hydrogen Eremets, M I; Troyan, I A
Nature materials,
12/2011, Volume:
10, Issue:
12
Journal Article
Peer reviewed
Molecular hydrogen is expected to exhibit metallic properties under megabar pressures. This metal is predicted to be superconducting with a very high critical temperature, T(c), of 200-400 K, and it ...may acquire a new quantum state as a metallic superfluid and a superconducting superfluid. It may potentially be recovered metastably at ambient pressures. However, experiments carried out at low temperatures, T<100 K, showed that at record pressures of 300 GPa, hydrogen remains in the molecular insulating state. Here we report on the transformation of normal molecular hydrogen at room temperature (295 K) to a conductive and metallic state. At 200 GPa the Raman frequency of the molecular vibron strongly decreased and the spectral width increased, evidencing a strong interaction between molecules. Deuterium behaved similarly. Above 220 GPa, hydrogen became opaque and electrically conductive. At 260-270 GPa, hydrogen transformed into a metal as the conductance of hydrogen sharply increased and changed little on further pressurizing up to 300 GPa or cooling to at least 30 K; and the sample reflected light well. The metallic phase transformed back at 295 K into molecular hydrogen at 200 GPa. This significant hysteresis indicates that the transformation of molecular hydrogen into a metal is accompanied by a first-order structural transition presumably into a monatomic liquid state. Our findings open an avenue for detailed and comprehensive studies of metallic hydrogen.
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The transformation of the socio-economic conditions of the functioning of service enterprises caused by the spread of the COVID-19 pandemic and the resulting economic crisis, actualize the study of ...the possibilities of ensuring their competitiveness. The article gives the analysis of the genesis and development of the content of the category of enterprise competitiveness in the basic concepts of economic theory. The author proposes a definition of the competitiveness of a service enterprise. The paper analyses traditional basic factors of enterprise competitiveness as well as substantiates the anti-crisis factors of maintaining the competitive maintenance of a service sector enterprise in the context of the current economic crisis related to the COVID-19 pandemic, such as: digitalization of business and the process of providing services, customer focus, virtualization of the workforce, cybersecurity, and the use of opportunities of the state anti-crisis policy.
The article examines the mentorship development in higher education. The need for a scientific reconsideration of the conceptual framework of mentorship in modern conditions, as well as its important ...practical significance for adapting students, improving the quality of education and professional activity are forming the relevance of this topic. The purpose of the article is to develop the concept of mentorship, to design a model and to plan the mentoring in higher education. An interdisciplinary approach was used to determine the essence of mentorship (consideration of the category in Psychology and Sociology, Pedagogy, Management), a model of mentorship in higher education has been developed with a structural-system analysis, as well as with graphical and statistical methods. The scientific novelty of the article is the development of the conceptual framework of mentoring and applied aspects of its implementation in higher education in Russia. The essential elements of mentorship were identified and considered, namely: the concept and approaches, purpose and objectives, principles and functions. The types of mentorship in higher education were classified according to key criteria: the number of mentees, formalization, period of interaction, method of implementation, direction of interaction, purpose. The main principles of mentoring in higher education are specified. A model of mentoring in higher education was proposed. A systematic analysis of successful practices and mentoring programs in higher education in Russia was carried out. The problems and prospects for mentorship development in modern conditions were identified. The practical significance of the study lies in the possibility of using conceptual developments in the formation and development of the legal framework for the implementation of mentoring, as well as the development and implementation of a mentoring model in higher education institutions.
Experimental syntheses of two iron polyhydrides FeH
x
(I) and FeH
x
(II) have been carried out in diamond anvil cells by laser heating of metallic iron to temperatures of about 700 and 2000 K at ...pressures of 178 and 195 GPa, respectively. The initial sample is an iron plate enriched in the Fe-57 Mössbauer isotope placed in ammonia borane (BH
3
NH
3
). The electronic properties of FeH
x
compounds have been studied by measuring the electrical resistance
R
(
T
) at high pressures (180–216 GPa) in the temperature range of ~8–300 K. Based on the obtained
R
(
T
) data, two superconducting phases of FeH
x
compounds with the maximum critical transition temperatures
T
c
≈ 25.0 and 27.7 K have been identified. It has been found that with increasing pressure, the temperature
T
c
in both hydrides increases linearly with the coefficients
dT
c
/
dP
~ 0.063 ± 0.001 K/GPa and 0.056 ± 0.003 K/GPa for the FeH
x
(I) and FeH
x
(II) phases, respectively. Superconductivity in iron hydrides revealed by the measured resistance
R
(
T
) has been confirmed by a number of additional methods.
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Specific features of thermal transformations of ferrocene Fe(C
5
H
5
)
2
at a pressure of 10 GPa upon laser heating to 2200 K have been investigated in diamond anvil cells. Maps of the temperature ...distribution on the sample during the heating have been obtained. The structure and properties of the transformation products have been studied by X-ray diffraction analysis, transmission electron microscopy, and Mössbauer spectroscopy. It is established that a characteristic feature of ferrocene transformations upon laser heating is the simultaneous formation of nanoparticles of iron (α-Fe) and iron carbide (Fe
7
C
3
) crystalline phases. The presence of α-Fe in the products of thermal transformations of ferrocene at high pressures has been observed for the first time. Possible mechanisms of the simultaneous formation of these nanoparticles during ferrocene transformations are discussed.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Iron polyhydrides have been synthesized at pressures of 77–157 GPa and temperatures up to 2000 K by the laser heating of an iron–borazane (ammonia borane NH
3
BH
3
) sample in diamond anvil cells. ...X-ray spectra of the synthesized products indicate the formation of several FeH
x
phases, in which (in two cells) reflections of FeH
iron hydride with the tetragonal
phase are reliably detected. The magnetic and electronic properties of FeH
x
compounds have been studied by nuclear forward scattering spectroscopy on Fe-57 nuclei at high pressures in the temperature range of 4–300 K in external magnetic fields up to 5 T. The nuclear forward scattering data indicate at least seven FeH
x
compounds with very different electronic and magnetic properties. The Néel temperature
T
N
determined for the FeH
2
phase at a pressure of 82 GPa is about 174 K. One of the striking results is the observation of the FeH
x
phase remaining magnetically ordered at a pressure of 128 GPa in the entire temperature range of 4–300 K. Such a high pressure is characteristic of the boundary between the lower mantle and the outer core of the Earth. The existence of a magnetic phase of an iron compound at such a record high pressure is unique and has not yet been observed.
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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
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