Showing papers on "Transition temperature published in 2008"
TL;DR: It is reported that a layered iron-based compound LaOFeAs undergoes superconducting transition under doping with F- ions at the O2- site and exhibits a trapezoid shape dependence on the F- content.
Abstract: We report that a layered iron-based compound LaOFeAs undergoes superconducting transition under doping with F- ions at the O2- site. The transition temperature (Tc) exhibits a trapezoid shape dependence on the F- content, with the highest Tc of ∼26 K at ∼11 atom %.
6,643 citations
TL;DR: In this article, the superconductivity of iron-based oxyarsenide Sm[O1-xFx]FeAs was reported, with the onset resistivity transition temperature at 55.0K and Meissner transition at 54.6 K. This compound has the same crystal structure as LaOFeAs with shrunk crystal lattices.
Abstract: We report the superconductivity in iron-based oxyarsenide Sm[O1-xFx]FeAs, with the onset resistivity transition temperature at 55.0K and Meissner transition at 54.6 K. This compound has the same crystal structure as LaOFeAs with shrunk crystal lattices, and becomes the superconductor with the highest critical temperature among all materials besides copper oxides up to now.
1,456 citations
TL;DR: It is reported that increasing the pressure causes a steep increase in the onset Tc of F-doped LaOFeAs, to a maximum of ∼43 K at ∼4 GPa, which is the highest Tc reported to date.
Abstract: The hunt for new materials exhibiting high-temperature superconductivity is on again. A complex iron-based oxide, containing lanthanum and arsenic, was recently found to exhibit a transition temperature (Tc) of about 26 K when doped with fluoride ions. That's respectable, but far from the heights achieved in copper oxide superconductors. Now Takahashi et al. show that the application of around 40,000 atmospheres of pressure can raise the Tc of this material substantially, to about 43 K. This is the highest tc yet reported for a non-copper-based material. What is more, this record is unlikely to last for long: the complexity of 'iron oxypnictides' of this type offers considerable flexibility for chemical modification, and we can expect to hear of yet higher transition temperatures. This paper — and the prospect of a new wave of superconductor fever — is the subject of an Editorial in the 24 April issue of Nature (452, 914; 2008). The application of pressure can raise the superconducting transition temperature of oxypnictide (a pnicogen being a group V element) substantially, to a maximum value of about 43 K. This is the highest transition temperature yet reported for a non-copper-based material, but this record is unlikely to last for long: the material system offers considerable flexibility for chemical modification, and we can reasonably anticipate that this record will soon be superseded. The iron- and nickel-based layered compounds LaOFeP (refs 1, 2) and LaONiP (ref. 3) have recently been reported to exhibit low-temperature superconducting phases with transition temperatures Tc of 3 and 5 K, respectively. Furthermore, a large increase in the midpoint Tc of up to ∼26 K has been realized4 in the isocrystalline compound LaOFeAs on doping of fluoride ions at the O2- sites (LaO1-xFxFeAs). Experimental observations5,6 and theoretical studies7,8,9 suggest that these transitions are related to a magnetic instability, as is the case for most superconductors based on transition metals. In the copper-based high-temperature superconductors, as well as in LaOFeAs, an increase in Tc is often observed as a result of carrier doping in the two-dimensional electronic structure through ion substitution in the surrounding insulating layers, suggesting that the application of external pressure should further increase Tc by enhancing charge transfer between the insulating and conducting layers. The effects of pressure on these iron oxypnictide superconductors may be more prominent than those in the copper-based systems, because the As ion has a greater electronic polarizability, owing to the covalency of the Fe–As chemical bond, and, thus, is more compressible than the divalent O2- ion. Here we report that increasing the pressure causes a steep increase in the onset Tc of F-doped LaOFeAs, to a maximum of ∼43 K at ∼4 GPa. With the exception of the copper-based high-Tc superconductors, this is the highest Tc reported to date. The present result, together with the great freedom available in selecting the constituents of isocrystalline materials with the general formula LnOTMPn (Ln, Y or rare-earth metal; TM, transition metal; Pn, group-V, ‘pnicogen’, element), indicates that the layered iron oxypnictides are promising as a new material platform for further exploration of high-temperature superconductivity.
1,084 citations
TL;DR: Although structural distortions are robust to changes in particle size, what is affected is the coherency of the distortions, which is decreased in the smaller particles, in contrast to the sharp transition that is found for the bulk sample.
Abstract: We have investigated the paraelectric-to-ferroelectric phase transition of various sizes of nanocrystalline barium titanate (BaTiO3) by using temperature-dependent Raman spectroscopy and powder X-ray diffraction (XRD). Synchrotron X-ray scattering has been used to elucidate the room temperature structures of particles of different sizes by using both Rietveld refinement and pair distribution function (PDF) analysis. We observe the ferroelectric tetragonal phase even for the smallest particles at 26 nm. By using temperature-dependent Raman spectroscopy and XRD, we find that the phase transition is diffuse in temperature for the smaller particles, in contrast to the sharp transition that is found for the bulk sample. However, the actual transition temperature is almost unchanged. Rietveld and PDF analyses suggest increased distortions with decreasing particle size, albeit in conjunction with a tendency to a cubic average structure. These results suggest that although structural distortions are robust to cha...
480 citations
TL;DR: In this paper, a layered iron-based compound LaOFeAs undergoes superconducting transition under doping with F- ions at the O2- site, and the transition temperature exhibits a trapezoid shape dependence on the F- content, with the highest Tc of ∼26 K at ∼11 atom %.
Abstract: We report that a layered iron-based compound LaOFeAs undergoes superconducting transition under doping with F- ions at the O2- site. The transition temperature (Tc) exhibits a trapezoid shape dependence on the F- content, with the highest Tc of ∼26 K at ∼11 atom %.
472 citations
TL;DR: In this article, the temperature dependence of line tension between liquid domains and of fluctuation correlation lengths in lipid membranes was quantitatively evaluated to obtain a critical exponent, nu = 1.2 +/- 0.2.
321 citations
TL;DR: In this paper, a series of oxygen-deficient, fluorine-free polycrystalline samples with nominal chemical formula NdFeAsO 1- y using high-pressure technique were synthesized.
Abstract: We have synthesized a series of oxygen-deficient, fluorine-free polycrystalline samples with nominal chemical formula NdFeAsO 1- y using high-pressure technique. The ZrCuSiAs type crystal structure, as expected for NdFeAsO, is formed as the main phase for the composition 0≤ y ≤0.6. Sharp superconducting (SC) transition with their transition temperature ( T c ) as high as 54 K is observed for 0.3≤ y ≤0.8 samples, which is higher than that of F-doped NdFeAsO. While T c does not depend on y , SC volume fraction shows maximum at y = 0.4. Around the same y , the lattice parameters show discontinuous shrinkage. These experimental results suggest the existence of a stable superconducting phase with a fixed atomic ratio close to Nd:Fe:As:O=1:1:1:0.6, presumably associated with a regular array of oxygen deficiency.
300 citations
TL;DR: It is shown that superconducting Cs(3)C(60) can be reproducibly isolated by solvent-controlled synthesis and has the highest Tc of any molecular material at 38 K, and the observed Tc maximum is attributed to the role of strong electronic correlations near the metal-insulator transition onset.
Abstract: C60-based solids are the archetypal molecular superconductors, reaching transition temperatures as high as 33 K. Now, Cs3C60 solids, having a transition temperature of 38 K, have been isolated. Both face-centred-cubic and body-centred-cubic phases were synthesized, and, uniquely among C60 solids, the superconducting phase was found to be body-centred cubic.
264 citations
TL;DR: In this article, the temperature dependence of the dielectric and ferroelectric properties of lead-free piezoceramics of the composition (1−x−y)Bi0.5Na 0.5NbO3 was investigated.
Abstract: The temperature dependence of the dielectric and ferroelectric properties of lead-free piezoceramics of the composition (1−x−y)Bi0.5Na0.5TiO3–xBaTiO3–yK0.5Na0.5NbO3 (0.05⩽x⩽0.07, 0.01⩽y⩽0.03) was investigated. Measurements of the polarization and strain hystereses indicate a transition to predominantly antiferroelectric order when heating from room temperature to 150°C, while for 150
225 citations
TL;DR: In this article, the fabrication and superconductivity of the iron-based arsenic oxide GdFeAsO1−δ compound with oxygen-deficiency was reported, which has an onset resistivity transition temperature at 53.5
Abstract: Here we report the fabrication and superconductivity of the iron-based arsenic oxide GdFeAsO1−δ compound with oxygen-deficiency, which has an onset resistivity transition temperature at 53.5 K. This material has the same crystal structure as the newly discovered high-Tc ReFeAsO1−δ family (Re = rare earth metal) and a further reduced crystal lattice, while the Tc starts to decrease compared with the SmFeAsO1−δ system.
186 citations
TL;DR: In this article, pressure-induced superconductivity in a single crystal of CaFe2As2 has been shown to be superconducting at atmospheric pressure of 0.69 GPa with a transition temperature exceeding 10 K.
Abstract: We report pressure-induced superconductivity in a single crystal of CaFe2As2. At atmospheric pressure, this material is antiferromagnetic below 170 K but under an applied pressure of 0.69 GPa becomes superconducting, with a transition temperature Tc exceeding 10 K. The rate of Tc suppression with applied magnetic field is −0.7 K T−1, giving an extrapolated zero-temperature upper critical field of 10–14 T.
TL;DR: In this article, a dome-like Ni doping dependence of superconducting transition temperature is discovered, and the Ni-doped system provides another example of the superconductivity induced by electron doping in the 122 phase.
Abstract: A series of 122 phase BaFe$_{2-x}$Ni$_x$As$_2$ ($x$ = 0, 0.055, 0.096, 0.18, 0.23) single crystals were grown by self flux method and a dome-like Ni doping dependence of superconducting transition temperature is discovered. The transition temperature $T_c^{on}$ reaches a maximum of 20.5 K at $x$ = 0.096, and it drops to below 4 K as $x$ $\geq$ 0.23. The negative thermopower in the normal state indicates that electron-like charge carrier indeed dominates in this system. This Ni-doped system provides another example of superconductivity induced by electron doping in the 122 phase.
TL;DR: In this article, the experimental and theoretical state of the art concerning the synthesis, properties and simulation of the new family and related systems is reviewed concerning the synthesisation, properties, and simulation.
Abstract: The discovery in February 2008 of superconductivity with the transition temperature about 26 K in fluorine-doped oxyarsenide LaO1–xFxFeAs stimulated numerous studies of superconducting and other physical properties of this and related materials, resulting in a new family of high-temperature (Tc ~ 26–55 K) superconductors.The experimental and theoretical state of the art is reviewed concerning the synthesis, properties and simulation of the new family and related systems.
TL;DR: In this paper, first-principles calculations and Monte Carlo simulation were used to predict ferromagnetic coupling in C doped CdS, resulting from carbon substitution of sulfur.
Abstract: Carbon doping of CdS is studied using first-principles calculations and Monte Carlo simulation. Our calculations predict ferromagnetism in C doped CdS, resulting from carbon substitution of sulfur. A single carbon substitution of sulfur favors a spin-polarized state with a magnetic moment of $1.22{\ensuremath{\mu}}_{B}$. Ferromagnetic coupling is generally observed between these magnetic moments. A transition temperature of $270\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is predicted through Monte Carlo simulation. The ferromagnetism of C doped CdS can be explained by the hole-mediated double exchange mechanism.
TL;DR: In this paper, it is shown that a part of VO2 powders have a "snowflake" morphology assembled by VO2 rods which have a monoclinic structure with a preferential orientation along 110 direction.
Abstract: Pure single-crystal rutile-type VO2 has been synthesized via the hydrothermal reaction of V2O5, oxalic acid, and tungstenic acid at low temperatures. The products have been characterized by means of X-ray diffraction, transmission electron microscopy, scanning electron microscopy, selected area electron diffraction, differential scanning calorimetry, and X-ray photoelectron spectroscopy. It is shown that a part of VO2 powders have a “snowflake” morphology assembled by VO2 rods which have a monoclinic structure with a preferential orientation along 110 direction. The adulterating agent tungstenic acid plays a key role in the synthesis of rutile phase. The DSC results indicated that the metal-semiconductor transition temperature of VO2 powders was reduced to room temperature or below. The reaction details and mechanisms are described and discussed. The substitution of a part of V atoms with larger W atoms induces the distortion of the VO6 octahedra, promoting the transition from VO2 (B) to VO2 (R).
TL;DR: In this paper, the fabrication and superconducting properties of GdO1−xFxFeAs were reported and it was found that when x is equal to 017, Gd o083F017FeAs is a superconductor with the onset transition temperature Tcon ≈ 366 K Resistivity anomaly near 130 K was observed for all samples up to x = 017.
Abstract: In this paper we report the fabrication and superconducting properties of GdO1−xFxFeAs It was found that when x is equal to 017, GdO083F017FeAs is a superconductor with the onset transition temperature Tcon ≈ 366 K Resistivity anomaly near 130 K was observed for all samples up to x = 017, and such a phenomenon is similar to that of LaO1−xFxFeAs Hall coefficient indicates that GdO1−xFxFeAs is conducted by electron-like charge carriers
TL;DR: In this paper, phase transitions and magnetic entropy changes are studied in Mn1.9−xNixGe (x=0.85, 0.855) alloys, and the effect of transition-metal vacancies on the phase transition temperature is discussed.
Abstract: Phase transitions and magnetic entropy changes are studied in Mn1.9−xNixGe (x=0.85, 0.855) alloys. In these off-stoichiometric alloys, the crystallographic transition temperature decreases remarkably due to the deficiency of transition-metal atoms, and, consequently, a magnetostructural transition from the antiferromagnetic TiNiSi-type structure to the ferromagnetic Ni2In-type structure is observed. Owing to the abrupt change in magnetization, large magnetic entropy changes are obtained. The effect of transition-metal vacancies on the phase transition temperature is discussed.
TL;DR: In this article, the effect of Bi 2 O 3 on the glass structure has been investigated by using Raman and infrared studies on these glasses in order to obtain information regarding the competitive role of the bi 2 o 3 in the formation of glass network.
TL;DR: In this article, pressure-induced superconductivity in a single crystal of CaFe2As2 has been shown to be superconducting under applied pressure of 0.69 GPa, with a transition temperature exceeding 10 K.
Abstract: We report pressure-induced superconductivity in a single crystal of CaFe2As2. At atmospheric pressure, this material is antiferromagnetic below 170 K but under an applied pressure of 0.69 GPa becomes superconducting, with a transition temperature Tc exceeding 10 K. The rate of Tc suppression with applied magnetic field is -0.7 K/T, giving an extrapolated zero-temperature upper critical field of 10-14T.
TL;DR: In this paper, the ferroelectric properties of barium zirconate titanate (BZT) ceramics were investigated by conventionally mixed-oxide method and it was shown that increasing Zr content in the BaTiO 3 -based compositions caused a decrease in Curie temperature.
TL;DR: In this paper, the effect of grain size on electrical and magnetic properties of La 0.67Sr0.33MnO3 nanoparticles with average grain size 32-85 nm has been investigated.
Abstract: The effect of grain size on electrical and magnetic properties of La0.67Sr0.33MnO3 nanoparticles with average grain size 32–85 nm has been investigated. The metal-insulator transition temperature TP gradually decreases with decreasing grain size, while the ferromagnetic-paramagnetic transition temperature TC remains almost constant. For the 32 nm sample, the larger effective magnetic moments and the deviation of the inverse susceptibility from the Curie–Weiss law are observed, indicating the possible existence of a Griffiths-like cluster phase. The ferromagnetic transition of the samples is further investigated by measuring magnetocaloric effect (MCE). The presence of short-range magnetic order greatly depresses the magnetic entropy of the paramagnetic phase. Moreover, the analysis of the MCE using Landau theory of phase transition confirms the importance of magnetoelastic coupling and electron interaction in magnetocaloric properties of manganites.
TL;DR: In this paper, the authors report magnetization and differential thermal analysis measurements as a function of pressure across the martensitic transition in magnetically superelastic Ni-Mn-In alloys.
Abstract: We report magnetization and differential thermal analysis measurements as a function of pressure across the martensitic transition in magnetically superelastic Ni–Mn–In alloys. It is found that the properties of the martensitic transformation are significantly affected by the application of pressure. All transition temperatures shift to higher values with increasing pressure. The largest rate of temperature shift with pressure has been found for Ni50Mn34In16 as a consequence of its small entropy change at the transition. Such a strong pressure dependence of the transition temperature opens up the possibility of inducing the martensitic transition by applying relatively low hydrostatic pressures.
TL;DR: In this paper, a nonlinear magnetic field dependence of the electronic specific heat coefficient γ(H) has been found in the low temperature limit, which is consistent with the prediction for a nodal superconductor.
Abstract: We report the specific heat measurements on the newly discovered Fe-based layered LaO0.9F0.1-δFeAs superconductor with the onset transition temperature Tc ≈ 28K. A nonlinear magnetic field dependence of the electronic specific heat coefficient γ(H) has been found in the low temperature limit, which is consistent with the prediction for a nodal superconductor. The maximum gap value Δ0 ≈ 3.4 ± 0.5 meV is derived by analysing γ(H) based on the d-wave model. We also detected the electronic specific heat difference between 9 T and 0 T in a wide temperature range, a specific heat anomaly can be clearly observed near Tc. The Debye temperature of our sample is determined to be about 315.7K. Our results suggest an unconventional mechanism for this new superconductor.
TL;DR: In this paper, Ta-sheathed superconducting wires were fabricated by the powder-in-tube method for the first time and the transition temperature of the wires was confirmed to be as high as 52 K.
Abstract: We report the fabrication of Ta-sheathed superconducting SmFeAsO1−xFx wires by the powder-in-tube method for the first time. The transition temperature of the SmFeAsO0.65F0.35 wires was confirmed to be as high as 52 K. High critical fields Hc2(0)≥120 T as well as current density Jc of 3900 A cm−2 at 5 K were also demonstrated. It should be noted that the Jc exhibits a very weak field dependence behavior, indicating a very encouraging prospect for application of the new superconductors.
TL;DR: In this paper, the 57Fe Mossbauer spectroscopy was applied to an iron-based layered superconductor LaO0.89F0.11FeAs with a transition temperature of 26 K and its parent material LaOFeAs.
Abstract: The 57Fe Mossbauer spectroscopy was applied to an iron-based layered superconductor LaO0.89F0.11FeAs with a transition temperature of 26 K and its parent material LaOFeAs. Throughout the temperature range from 4.2 to 298 K, a singlet spectrum with no magnetic splitting was observed as a main component of each Mossbauer spectrum of the F-doped superconductor. No additional internal magnetic field was observed for the spectrum measured at 4.2 K under a magnetic field of 7 T. On the other hand, the parent LaOFeAs shows a magnetic transition at around 140 K, and this temperature is slightly lower than that of a structural phase transition from tetragonal to orthorhombic phase, which accompanies the resistivity anomaly at around 150 K. The magnetic moment is estimated to be ~0.35 $\mu$B/Fe at 4.2 K in the orthorhombic phase, and the spin disorder remains in the magnetic ordered state even at 4.2 K. The fact that no magnetic transition in LaO0.89F0.11FeAs was observed even at 4.2 K under 7 T implies a strong spin fluctuation above Tc or small magnetic moment in this system. Therefore, the present results show that the F-doping effectively suppresses the magnetic and structural transitions in the parent material and the suppression leads to emergence of superconductivity in this system.
TL;DR: In this paper, the authors applied Fe Mossbauer spectroscopy to an iron-based layered superconductor LaFeAsO 0.89 F 0.11 with a transition temperature of 26 K.
Abstract: 57 Fe Mossbauer spectroscopy was applied to an iron-based layered superconductor LaFeAsO 0.89 F 0.11 with a transition temperature of 26 K and to its parent material LaFeAsO. Throughout the temperature range from 4.2 to 298 K, a singlet pattern with no magnetic splitting was observed in the Mossbauer spectrum of the F-doped superconductor. Furthermore, no additional internal magnetic field was observed for the spectrum measured at 4.2 K under a magnetic field of 7 T. On the other hand, magnetically split spectra were observed in the parent LaFeAsO below 140 K, and this temperature is slightly lower than that of a structural phase transition from tetragonal to orthorhombic phase, which accompanies the electrical resistivity anomaly at around 150 K. The magnetic moment is estimated to be ∼0.35 µ B /Fe from the internal magnetic field of 5.3 T at 4.2 K in the orthorhombic phase, and the spin disorder appears to remain in the magnetically ordered state even at 4.2 K. The lack of a magnetic transition in LaFeA...
TL;DR: W-doped vanadium dioxide thin films were deposited by Aerosol Assisted Chemical Vapour Deposition (AACVD) in this article, where they were characterised with several different techniques (i.e., X-ray Diffraction, Raman, Scanning Electron Microscopy-Energy Dispersive X-Ray Analysis), to determine their composition and morphology.
TL;DR: In this paper, the effect of molybdenum and tungsten co-doping on semiconductor-metal transition of vanadium dioxide films is investigated, and it is compared with single moly bdenum doped and undoped films.
01 Jan 2008
TL;DR: In this paper, the same authors showed that the surface morphology of pure VO2 films revealed elongated grains oriented within the film plane, and the doped ones showed an increased tendency to be oriented out of the film planes as well as increased roughnes s.
Abstract: The latest approach on the improvement the energy e fficiency of buildings is based on the use of thermochromic coatings on so-called “smart” windows. These coatings possess the ability of changing their optical properties as a c onsequence of a reversible structural transformation when going through a critical temper ature. Vanadium dioxide is an example of a transparent thermochromic material which is a pro mising candidate for this kind of application. The change on its optical and also ele ctrical properties takes place at 68oC as a result of a first-order structural transition, know n as Mott transition [1], going from a monoclinic to a tetragonal phase on heating. The lo w temperature semiconducting phase which is transparent to radiation in the visible an d infrared wavelength range maximizes the heating due to blackbody radiation, while the metal lic high temperature phase blocks the infrared radiation and maintains at the same time t he transparency required, in the visible range, to keep an environment of natural light. A t ransition temperature of 68oC is too high for this application and must therefore be reduced. Tungsten-doping of VO2 has demonstrated to decrease the transition temperature in the great est extent, when compared with other metals, and has therefore been the focus of most of the research [2]. In the current study, VO 2 thin films doped with different W at.% and consequ ent dissimilar switching temperatures, were successfull y deposited onto SiO2-coated float-glass substrates by reactive direct current (DC) magnetro n sputtering. The doping methodology associated with optimized processing conditions all owed the production of W-doped VO2 films with reduced switching temperatures and maximum transmittances at the visible region ranging 40%. Structural analyses have shown, for un doped films, single phase VO2(M) films with (002) as the preferred crystal orientation pla ne. The addition of W favors the crystallization in the (011) direction which become s dominant above a critical level of dopant concentration. The surface morphology of pure VO2 films revealed elongated grains oriented within the film plane, and the doped ones have show n an increased tendency to be oriented out of the film plane as well as increased roughnes s. The relationship between W contents in the film and consequent transition temperature pres ented a linear behavior.
TL;DR: In this article, the temperature dependence of the dielectric permittivity of perovskite Ba(ZrxTi1−x)O3 solid solutions, PbMg1/3Nb2/3O3 relaxor, and BaTiO3 ferroelectric ceramics was measured.
Abstract: The temperature dependence of the dielectric permittivity of perovskite Ba(ZrxTi1−x)O3 solid solutions, PbMg1/3Nb2/3O3 relaxor, and BaTiO3 ferroelectric ceramics was measured. It is found that a Lorentz-type law can be used to describe the dielectric permittivity of either the normal ferroelectrics with or without diffuse phase transitions (DPT) or the typical ferroelectric relaxors. The ferroelectric DPT can be well described by just one fitting process using the Lorentz-type law, while the relaxor ferroelectric transition needs two independent fitting processes. The Lorentz-type law fails at the low temperature side of the dielectric maximum of a first-order ferroelectric phase transition. Above the transition temperature, the dielectric curves of all the studied materials can be well described by a Lorentz-type law.