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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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
The magnetic and electronic states of iron in the hexagonal close-packed ε-Fe phase have been studied by synchrotron Mössbauer spectroscopy on Fe-57 nuclei (nuclear forward scattering method) at ...pressures of
GPa in the temperature range of 4–300 K in external magnetic fields up to 5 T. It has been found that Fe atoms are in a nonmagnetic state in the entire studied
P
–
T
region. Theoretically implied magnetic instability and quantum spin fluctuations, which can be stabilized by magnetic perturbation (e.g., external magnetic field), have not been confirmed by our measurements of nuclear forward scattering spectra in an external magnetic field. It has been established that the isomer shift
IS
(
P
) has a nonlinear pressure dependence and reaches a colossal value of about –0.8 mm/s at a maximum pressure of 241 GPa, indicating a very high electron density on the Fe nucleus. A sharp change in the electron density on the Fe nucleus at temperatures of 100–200 K indicates a phase transition with a change in the electronic structure, which can be due to an abrupt increase in the conductivity or even to the appearance of superconductivity.
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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
4.
Single-bonded cubic form of nitrogen Eremets, Mikhail I; Gavriliuk, Alexander G; Trojan, Ivan A ...
Nature materials,
08/2004, Volume:
3, Issue:
8
Journal Article
Peer reviewed
Nitrogen usually consists of molecules where two atoms are strongly triple-bonded. Here, we report on an allotropic form of nitrogen where all atoms are connected with single covalent bonds, similar ...to carbon atoms in diamond. The compound was synthesized directly from molecular nitrogen at temperatures above 2,000 K and pressures above 110 GPa using a laser-heated diamond cell. From X-ray and Raman scattering we have identified this as the long-sought-after polymeric nitrogen with the theoretically predicted cubic gauche structure (cg-N). This cubic phase has not been observed previously in any element. The phase is a stiff substance with bulk modulus >or=300 GPa, characteristic of strong covalent solids. The polymeric nitrogen is metastable, and contrasts with previously reported amorphous non-molecular nitrogen, which is most likely a mixture of small clusters of non-molecular phases. The cg-N represents a new class of single-bonded nitrogen materials with unique properties such as energy capacity: more than five times that of the most powerfully energetic materials.
The vibrational properties of yttrium iron garnet Y
3
Fe
5
O
12
at a high quasihydrostatic pressure are studied by the Raman spectroscopy method. Raman spectra are measured in a high-pressure diamond ...anvil cell in the pressure range of 0–72 GPa at room temperature. A fundamental change in the character of spectra with the disappearance of sharp peaks is detected near ~50 GPa. This confirms a phase transition from the crystalline to amorphous state, which was previously detected by other experimental methods. This transition is accompanied by spin crossover in Fe
3+
ions, which transit from the high-spin (HS,
S
= 5/2) to low-spin (LS,
S
= 1/2) state. The pressure dependences of phonon modes in Y
3
Fe
5
O
12
are measured from atmospheric pressure to the critical phase transition pressure.
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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
Pressure‐stabilized hydrides are a new rapidly growing class of high‐temperature superconductors, which is believed to be described within the conventional phonon‐mediated mechanism of coupling. ...Here, the synthesis of one of the best‐known high‐TC superconductors—yttrium hexahydride Im3¯m‐YH6 is reported, which displays a superconducting transition at ≈224 K at 166 GPa. The extrapolated upper critical magnetic field Bc2(0) of YH6 is surprisingly high: 116–158 T, which is 2–2.5 times larger than the calculated value. A pronounced shift of TC in yttrium deuteride YD6 with the isotope coefficient 0.4 supports the phonon‐assisted superconductivity. Current–voltage measurements show that the critical current IC and its density JC may exceed 1.75 A and 3500 A mm−2 at 4 K, respectively, which is higher than that of the commercial superconductors, such as NbTi and YBCO. The results of superconducting density functional theory (SCDFT) and anharmonic calculations, together with anomalously high critical magnetic field, suggest notable departures of the superconducting properties from the conventional Migdal–Eliashberg and Bardeen–Cooper–Schrieffer theories, and presence of an additional mechanism of superconductivity.
Novel yttrium hexahydride YH6 is synthesized, an outstanding high‐TC superconductor with critical temperature of 224–226 K and unexpectedly large upper critical magnetic field ≈116–158 T. YH6 demonstrates high critical current density of ≈3500 A mm−2 at 4 K, which is above that of NbTi and YBCO. This study points to a possible additional nonconventional contribution to superconductivity in YH6.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The aim of this study was to investigate the relationship of metabolic and immunological disorders in acute tetrachlomethane, ischemic and alcoholic liver damage modelled in adult Wistar male rats ...weighing 120-160 g. After evaluation of metabolic and immunological parameters at the local and systemic levels, and correlation analysis was used to establish the relationship between the dynamics of the indicators against the background of experimental pathology models. The close correlation between the studied immune and metabolic parameters recognized for the tetrachlomethane, ischemic and alcoholic liver damage shows the existing "tension" between the indicators of immune and metabolic status. Such close correlation between the studied immunological and metabolic parameters at the system and local levels can serve to assess the severity of the disease, its prognosis, treatment effectiveness and preventive measures.
The crystal structure of tin selenide SnSe has been studied under quasihydrostatic compression at pressures up to 205 GPa created in diamond anvil cells at room temperature. Two structural phase ...transitions have been detected at and
P
≈ 2.5 32 GPa. The former phase transition is continuous from the GeS-type structure (space group
Pbnm
) to the TlI-type structure (space group
Cmcm
). The phase transition to the CsCl-type cubic structure (space group
Pm
3
¯
m
) occurs at 32 GPa and is accompanied by a stepwise decrease in the volume of the unit cell by 7%. The pressure dependence of the specific volume of the unit cell at room temperature has been constructed up to 205 GPa.
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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
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