Synchrotron X-ray diffraction studies of the structural characteristics of Ba
3
TaFe
3
Si
2
O
14
langasite are performed at high hydrostatic pressures (up to 60 GPa) created in a diamond anvil cell. ...At pressures up to 20 GPa, the Mössbauer absorption spectra for
57
Fe nuclei and the Raman spectra are recorded. Two structural phase transitions at
P
≈ 5.5 and 20 GPa are observed. The first transition corresponds to the displacements of light oxygen atoms and to an increase in the local symmetry of 3
f
oxygen tetrahedra surrounding iron ions. The second one is accompanied by a pronounced change in the lattice parameter
c
, and the unit cell volume undergoes a stepwise drop as large as 8.6%. An appreciable decrease in the parameter
c
at the structural transition should result in a significant increase in the exchange coupling constants between iron ions in neighboring
ab
planes underlying the giant increase in the Néel temperature in this crystal at pressures exceeding 20 GPa.
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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, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The spin states of Fe
2+
ions in (Mg
0.75
,Fe
0.25
)O magnesiowüstite crystals at hydrostatic pressures up to 90 GPa created in a diamond-anvil cell with helium as a pressure-transmitting medium have ...been investi-gated by transmission and synchrotron Mössbauer spectroscopy at room temperature. An electron transition from the high-spin (HS) state to the low-spin (LS) state (HS-LS crossover) has been observed in the pressure range of 55–70 GPa. The true HS-LS transition occurs in a narrow pressure range and the extension of the electron transition to ∼15 GPa is attributed to the effect of the nearest environment and to thermal fluctuations between the high-spin and low-spin states at finite temperatures. It has been found that the lowest pressure at which the electron HS-LS transition can occur in the Mg
1 −
x
Fe
x
system is 50–55 GPa.
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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, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The electrical resistance of FeBO
3
crystals at high and ultrahigh pressures (up to 198 GPa) and low temperatures has been measured using diamond anvil cells. It has found that in the high-pressure ...phase, 46 GPa <
P
< 100 GPa, the activation energy
E
ac
decreases gradually from 0.55 to 0.3 eV according to a linear law. Its extrapolation to zero gives an estimated value of about 210 GPa for the pressure at which complete metallization is expected. However, above 100 GPa, the linear
E
ac
(
P
) dependence smoothly transforms to a nonlinear one. At the same time, the temperature dependence of the electrical resistance at fixed pressure significantly deviates from the Arrhenius activation law and does not obey the Mott law for the hopping conductivity. Experimental data demonstrate the dependence of the activation energy
E
ac
both on pressure and temperature. At
T
= 0, the gap tends to zero. Theoretical analysis shows that the decrease in
E
ac
upon cooling can be interpreted in terms of the transition of the low-spin FeBO
3
phase to the magnetically ordered (antiferromagnetic) state.
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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
Experimental results from the synthesis of diamond-like BC
x
compounds with the aid of high-pressure techniques and laser sputtering methods are presented. A combination of unique characteristics in ...these compounds can be attained by varying the B/C ratio. The possibility of sputtering carbon films of micron or nanosize thickness with high boron content opens up a way to use such materials on industrial scales. Hetero-diamonds with high boron content have high elastic moduli and boron-doped diamond polycrystals possess metallic conductivity.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The discovery of new high-temperature superconductors based on FeAs has led to a new 'gold rush' in high-T(C) superconductivity. All of the new superconductors share the same common structural motif ...of FeAs layers and reach T(C) values up to 55 K (ref. 2). Recently, superconductivity has been reported in FeSe (ref. 3), which has the same iron pnictide layer structure, but without separating layers. Here, we report the magnetic and electronic phase diagram of beta-Fe(1.01)Se as a function of temperature and pressure. The superconducting transition temperature increases from 8.5 to 36.7 K under an applied pressure of 8.9 GPa. It then decreases at higher pressures. A marked change in volume is observed at the same time as T(C) rises, owing to a collapse of the separation between the Fe(2)Se(2) layers. No static magnetic ordering is observed for the whole p-T phase diagram. We also report that at higher pressures (starting around 7 GPa and completed at 38 GPa), Fe(1.01)Se transforms to a hexagonal NiAs-type structure and exhibits non-magnetic behaviour.
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