Intercalation effect on hyperfine parameters of Fe in FeSe superconductor with Tc = 42 K

57Fe-Mossbauer spectra of superconducting beta-FeSe, the Li/NH3 intercalate product and a subsequent sample of this intercalate treated with moist He gas have been measured in temperature range 4.7 - 290 K. A correlation is established between hyperfine parameters and critical temperature Tc in these phases. A strong increase of isomer shift upon intercalation is explained by a charge transfer from the Li/NH3 intercalate to the FeSe layers resulting in an increase of Tc up to 42 K. A significant decrease of the quadrupole splitting above 240 K has been attributed to diffusive motion of Li+ ions within the interlamellar space.Comment: 6 pages, 5 figures, 1 tabl

Pressure-induced magnetic collapse and metallization of TlFe1.6Se2\mathrm{TlF}{\mathrm{e}}_{1.6}\mathrm{S}{\mathrm{e}}_{2}

The crystal structure, magnetic ordering, and electrical resistivity of TlFe1.6Se2 were studied at high pressures. Below ~7 GPa, TlFe1.6Se2 is an antiferromagnetically ordered semiconductor with a ThCr2Si2-type structure. The insulator-to-metal transformation observed at a pressure of ~ 7 GPa is accompanied by a loss of magnetic ordering and an isostructural phase transition. In the pressure range ~ 7.5 - 11 GPa a remarkable downturn in resistivity, which resembles a superconducting transition, is observed below 15 K. We discuss this feature as the possible onset of superconductivity originating from a phase separation in a small fraction of the sample in the vicinity of the magnetic transition.Comment: 12 pages, 5 figure

Conventional and unconventional superconductivity in chalcogenides under high pressure

A superconductor is a material that can conduct electricity without resistance below a critical temperature Tc. Nowadays, technological applications of superconductors include the design of electromagnets, which are used in MRI/NMR machines, mass spectrometers, particle accelerators, and Josephson junctions, which are the building blocks of the most sensitive magnetometers, particle detectors, including superconducting bolometers and transition edge sensors, as well as low-loss power cables and power storage devices. Therefore, the investigation of high-temperature superconductors is one the most important and challenging problems in the field of solid-state physics and chemistry. Iron chalcogenides are a relatively young and promising family of superconductors. Since the nature of superconductivity in these materials is not fully understood (they are unconventional superconductors), the prospects for the development of their properties are not clear. Applying Mössbauer spectroscopy techniques in combination with magnetic susceptibility and transport measurements under pressure to the simplest systems based mainly on FeSe, we showed how magnetism and superconductivity interact in iron chalcogenides. Magnetic and/or superconducting properties of these materials can be tuned via metal doping, chalcogen substitution or chemical intercalation. Spin fluctuations in high-Tc Lix(NH2)y(NH3)1-yFe2Se2 were shown to be responsible for superconducting pairing at ambient and under applied pressure. For FeSe0.5Te0.5, the electronic phase diagram was investigated, and a structural phase transition associated with disappearance of superconductivity was described. Phase separation in ThCr2Si2-type superconductors was probed by chemical modification using Mössbauer spectroscopy. It was shown that interplay between antiferromagnetic and paramagnetic iron centres, which are responsible for superconducting pairing in RbxFeySe2 series, might be tuned by doping or varying stoichiometry. In contrast to Fe-based materials, metallization of hydrogen sulfide under pressure leaded to the appearance of conventional superconductivity with Tc as high as 203 K, which is 39 K above the previous record in cuprate superconductors. The Meissner effect in H2S under pressure of 155 GPa was demonstrated. Its fundamental parameters, critical field, London penetration depth and coherence length, were found and evidenced that H2S under pressure is a type-II superconductor. A pronounced isotope shift of Tc in D2S suggested an electron-phonon mechanism of superconductivity that is consistent with the Bardeen–Cooper–Schrieffer scenario. The latest says that the presence of hydrogen is a key to the record-high Tc, raising the prospect that even higher transition temperatures – possibly even approaching room temperature – will be discovered in other hydrogen-dominant systems.Supraleiter ist ein Material, das Strom ohne Widerstand unterhalb einer kritischen Temperatur Tc leiten kann. Heutzutage beinhalten technologische Anwendungen von Supraleitern die Konstruktion von Elektromagneten, die in MRI / NMR-Maschinen, Massenspektrometern, Teilchenbeschleunigern und Josephson-Übergängen verwendet werden, die die Bausteine ​​der empfindlichsten Magnetometer, Teilchendetektoren, einschließlich supraleitender Bolometer und Übergang sind Kanten-Sensoren, sowie verlustarme Stromkabel und Stromspeicher. Daher ist die Untersuchung von Hochtemperatur-Supraleitern eines der wichtigsten und herausfordernden Probleme auf dem Gebiet der Festkörperphysik und Chemie. Eisenchalcogenide sind eine relativ junge und vielversprechende Familie von Supraleitern. Da die Natur der Supraleitung in diesen Materialien nicht vollständig verstanden wird (sie sind unkonventionelle Supraleiter), sind die Aussichten für die Entwicklung ihrer Eigenschaften nicht klar. Bei der Anwendung von Mössbauer-Spektroskopie-Techniken in Kombination mit magnetischer Suszeptibilität und Transportmessungen unter Druck auf die einfachsten Systeme, die hauptsächlich auf FeSe basieren, haben wir gezeigt, wie Magnetismus und Supraleitung in Eisenchalcogeniden wechselwirken. Magnetische und / oder supraleitende Eigenschaften dieser Materialien können über Metalldotierung, Chalkogensubstitution oder chemische Interkalation abgestimmt werden. Spin-Fluktuationen in High-Tc Lix (NH2) y (NH3) 1-yFe2Se2 wurden für die supraleitende Paarung bei Umgebungstemperatur und unter angelegtem Druck verantwortlich gemacht. Für FeSe0.5Te0.5 wurde das elektronische Phasendiagramm untersucht und ein struktureller Phasenübergang, der mit dem Verschwinden der Supraleitung verbunden ist, beschrieben. Die Phasentrennung in ThCr2Si2-Supraleitern wurde durch chemische Modifikation mittels Mössbauer-Spektroskopie untersucht. Es wurde gezeigt, dass das Zusammenspiel von antiferromagnetischen und paramagnetischen Eisenzentren, die für die supraleitende Paarung in der RbxFeySe2-Reihe verantwortlich sind, durch Dotierung oder variierende Stöchiometrie abgestimmt werden könnte. Im Gegensatz zu Fe-basierten Materialien führte die Metallisierung von Schwefelwasserstoff unter Druck auf das Aussehen der konventionellen Supraleitung mit Tc bis zu 203 K, was 39 K über dem bisherigen Rekord in Cuprat-Supraleitern liegt. Der Meissner-Effekt bei H2S unter einem Druck von 155 GPa wurde nachgewiesen. Seine grundlegenden Parameter, das kritische Feld, die Londoner Eindringtiefe und die Kohärenzlänge wurden gefunden und belegt, dass H2S unter Druck ein Typ-II-Supraleiter ist. Eine ausgeprägte Isotopenverschiebung von Tc in D2S schlug einen Elektron-Phonon-Mechanismus der Supraleitung vor, der mit dem Bardeen-Cooper-Schrieffer-Szenario übereinstimmt. Die neueste sagt, dass die Anwesenheit von Wasserstoff ein Schlüssel für den Rekordhoch Tc ist, was die Aussicht aufbaut, dass noch höhere Übergangstemperaturen - eventuell sogar annähernde Raumtemperatur - in anderen Wasserstoff-dominanten Systemen entdeckt werden

Pyridinium bis(pyridine-κN)tetrakis(thiocyanato-κN)ferrate(III) -pyrazine-2-carbonitrile-pyridine (1/4/1)

In the title compound, (C5H6N)[Fe(NCS)4(C5H5N)2]- 4C5H3N3C5H5N, the FeIII ion is located on an inversion centre and is six-coordinated by four N atoms of the thiocyanate ligands and two pyridine N atoms in a trans arrangement, forming a slightly distorted octahedral geometry. A half-occupied H atom attached to a pyridinium cation forms an N—HN hydrogen bond with a centrosymmetrically-related pyridine unit. Four pyrazine-2-carbonitrile molecules crystallize per complex anion. In the crystal, – stacking interactions are present [centroid–centroid distances = 3.6220 (9), 3.6930 (9), 3.5532 (9), 3.5803 (9) and 3.5458 (8) A˚ ].peerReviewe

Synthesis of Nanocrystals and Particle Size Effects Studies on the Thermally Induced Spin Transition of the Model Spin Crossover Compound [Fe(phen) 2 (NCS) 2 ]

International audienc

Photoinduced hole transfer from tris(bipyridine)ruthenium dye to a high-valent iron-based water oxidation catalyst

An efficient water oxidation system is a prerequisite for developing solar energy conversion devices. Using advanced time-resolved spectroscopy, we study the initial catalytic relevant electron transfer events in the light-driven water oxidation system utilizing [Ru(bpy)(3)](2+) (bpy = 2,2 '-bipyridine) as a light harvester, persulfate as a sacrificial electron acceptor, and a high-valent iron clathrochelate complex as a catalyst. Upon irradiation by visible light, the excited state of the ruthenium dye is quenched by persulfate to afford a [Ru(bpy)(3)](3+)/SO4- pair, showing a cage escape yield up to 75%. This is followed by the subsequent fast hole transfer from [Ru(bpy)(3)](3+) to the Fe-IV catalyst to give the long-lived Fe-V intermediate in aqueous solution. In the presence of excess photosensitizer, this process exhibits pseudo-first order kinetics with respect to the catalyst with a rate constant of 3.2(1) x 10(10) s(-1). Consequently, efficient hole scavenging activity of the high-valent iron complex is proposed to explain its high catalytic performance for water oxidation

Solvent-dependent SCO Behavior of Dinuclear Iron(II) Complexes with a 1,3,4-Thiadiazole Bridging Ligand

Two dinuclear iron­(II) complexes [Fe₂(μ-L)₂]­X₄*4DMF (X = BF₄^– (<b>1·4DMF</b>) and ClO₄^– (<b>2·4DMF</b>)) with a 1,3,4-thiadiazole bridging ligand have been synthesized and show a very distinct solvent-depending SCO behavior. The complexes represent new solvatomorphs of the first dinuclear iron­(II) complexes with the ligand L (2,5-bis­[(2-pyridylmethyl)­amino]­methyl-1,3,4-thiadiazole). The incorporated lattice DMF molecules directly affect the spin state of these complexes. This behavior reveals a structural insight into the role of the solvent molecules on the spin transition

Hofmann-Like Frameworks Fe(2-methylpyrazine)n[M(CN)2]2 (M = Au, Ag) : Spin-Crossover Defined by the Precious Metal

Hofmann-like cyanometalates constitute a large class of spin-crossover iron(II) complexes with variable switching properties. However, it is not yet clearly understood how the temperature and cooperativity of a spin transition are influenced by their structure. In this paper, we report the synthesis and crystal structures of the metal–organic coordination polymers {FeII(Mepz)[AuI(CN)2]2} ([Au]) and {FeII(Mepz)2[AgI(CN)2]2} ([Ag]), where Mepz = 2-methylpyrazine, along with characterization of their spin-state behavior by variable-temperature SQUID magnetometry and Mössbauer spectroscopy. The compounds are built of cyanoheterometallic layers, which are pillared by the bridging Mepz ligands in [Au] but separated in [Ag]. The complex [Au] exhibits an incomplete stepped spin transition as a function of the temperature with TSCO1 = 170 K and TSCO2 = 308 K for the two subsequent steps. In contrast, the complex [Ag] attains the high-spin state over the whole temperature range. In the crystal structure of [Ag], weak interlayer contacts (Ag−π, Me−π, and Ag–N) are found that may be responsible for an unusual axial elongation of the FeN6 polyhedra. We propose that this structural distortion contributes to the trapping of iron in its high-spin state

1D iron(ii)-1,2,4-triazolic chains with spin crossover assembled from discrete trinuclear complexes

Temperature-induced spin crossover has been found in a molecular ferrous complex of 4-amino-1,2,4-triazole for the FeN6 centres, while the FeN3O3 centres are always HS