Search

Multi-layered iron-based superconducting wires were developed using a tape-in-tube method. The interface between the superconducting filament and the Ag matrix is found to play an important role in the phase homogeneity and current carrying performance.

Funding: This research was carried out in part due to funding from the Max Planck-UBC-UTokyo Centre for Quantum Materials. Part of the research described in this paper was performed at the Canadian Light Source, a national research facility of the University of Saskatchewan, which is supported by the Canada Foundation for Innovation, the Natural Sciences and Engineering Research Council, the National Research Council, the Canadian Institutes of Health Research, the Government of Saskatchewan and the University of Saskatchewan. We thank the Science and Technology Facilities Council ISIS facility for the provision of beamtime. (Ba,K)BiO3 constitute an interesting class of superconductors, where the remarkably high superconducting transition temperature Tc of 30 K arises in proximity to charge density wave order. However, the precise mechanism behind these phases remains unclear. Here, enabled by high-pressure synthesis, we report superconductivity in (Ba,K)SbO3 with a positive oxygen–metal charge transfer energy in contrast to (Ba,K)BiO3. The parent compound BaSbO3−δ shows a larger charge density wave gap compared to BaBiO3. As the charge density wave order is suppressed via potassium substitution up to 65%, superconductivity emerges, rising up to Tc = 15 K. This value is lower than the maximum Tc of (Ba,K)BiO3, but higher by more than a factor of two at comparable potassium concentrations. The discovery of an enhanced charge density wave gap and superconductivity in (Ba,K)SbO3 indicates that strong oxygen–metal covalency may be more essential than the sign of the charge transfer energy in the main-group perovskite superconductors. Publisher PDF

Iron-based superconductor, a promising candidate for high-field applications, has attracted significant attentions. For practical utilization, the superconducting tapes should have high transport critical current density (Jc), low production cost, larger mechanical strength and good homogeneity. In this study, seven-filament Cu/Ag-sheathed (Ba,K)Fe2As2 tapes were fabricated from round and square wires. It is found that the tapes rolled from square wires have a desirable uniformity of filament deformation and distribution, compared with the ones rolled from round wires. Moreover, the Jc of tape was obviously improved by using square drawing dies instead of traditional round ones. For the tapes rolled from square wires annealed under ambient and 2 MPa by hot pressing, the transport Jc values reached 1.51 × 104 A·cm−2 and 4.86 × 104 A·cm−2 (4.2 K, 10 T), respectively. The deformation process on the cross section of the tapes during rolling was analyzed by using the powder-flow model. These results indicate a potential application of Cu/Ag (Ba,K)Fe2As2 tapes in high-magnetic-field region.

The electronic structure, lattice dynamics, and electron-phonon coupling (EPC) of the newly discovered (Ba,K)SbO$_3$ superconductors are investigated by first-principles calculations. The EPC of (Ba,K)SbO$_3$ is significantly enhanced by considering non-local electronic correlation using the Heyd-Scuseria-Ernzerhof hybrid exchange-correlation functional (HSE06). The EPC strength {\lambda} of Ba$_{0.35}$K$_{0.65}$SbO$_3$ is strongly increased from 0.33 in local-density approximation calculations to 0.59 in HSE06 calculations, resulting in a superconducting transition temperature Tc of about 14.9 K, which is in excellent agreement with experimental value of ~ 15 K. Our findings suggest (Ba,K)SbO$_3$ are extraordinary conventional superconductors, where non-local electronic correlation expands the bandwidth, enhances the EPC, and boosts the Tc. Moreover, we find both {\lambda} and Tc depend crucially on the K-doping level for (Ba,K)SbO$_3$ and (Ba,K)SbO$_3$ compounds. (Ba,K)SbO$_3$ have stronger EPC strength and higher Tc than those of (Ba,K)SbO$_3$ at the same K-doping level., Comment: 29 pages, 10 figures

xBaO–(20−x)K2O–30TiO2–50P2O5 with (0≤x≤20 mol%) glasses were successfully elaborated by the melt quenching while their related glass-ceramics were developed by controlled crystallisation. Density and molar volume measurements, differential thermal analysis and Raman spectroscopy were carried out to examine the glassy structure, the results revealed that the addition of BaO increases the reticulation and reinforces the glass network by the creation of strengthened linkages. X-ray diffraction has identified the formation of MTi2(PO4)3 with M=(K, Ba0·5) in all the glass-ceramics (GC) and the precipitation of a secondary BaTiP2O8 phase when x increase beyond 10 mol%. The dielectric properties of the glass-ceramics were studied by impedance spectroscopy, it showed that the addition of BaO induces an enhancement of both thermal and frequency stability of the dielectric parameters (εr and tanδ). The glass-ceramic with 5 mol% of BaO GC-(x=5) presents the highest dielectric constant and the lowest dielectric loss. The P-E hysteresis loops were recorded at room temperature and the energy storage parameters of the glass-ceramics were determined. These parameters were significantly improved by the increase of the BaO content and the optimum parameters were obtained for GC-(x=5). The dielectric and energy storage parameters were discussed according to the structure data.

The compound Ba1–xKxZn2As2 has a low-temperature phase (α-phase) crystallized in the α-BaCu2S2-type structure and a high-temperature phase (β-phase) crystallized in the ThCr2Si2-type structure. We ...

(Ba,K)BiO

The most effective way to enhance the dissipation-free supercurrent in presence of magnetic field for type II superconductors is the introduction of defects that acts as artificial pinning centres (APCs) for the vortices. For instance, the in-field critical current density of doped BaFe2As2 (Ba122), one of the most technologically important Fe-based superconductors, has been improved over the last decade by APCs created by ion-irradiation. The technique of ion-irradiation has been commonly implemented to determine the ultimate superconducting properties. However, this method is rather complicated and expensive. Here, we report on a surprisingly high critical current density and strong pinning efficiency close to the crystallographic c-axis for a K-doped Ba122 epitaxial thin film without APCs, achieving performance comparable to ion-irradiated K-doped Ba122 single crystals. Microstructural analysis reveals that the film is composed of columnar grains having width around 30-60 nm. The grains are rotated around the b- (or a-) axis by 1.5 degree and around the c-axis by -1 degree, resulting in the formation of low-angle grain boundary networks. This study demonstrates that the upper limit of in-field properties reached in ion-irradiated K-doped Ba122 is achievable by grain boundary engineering, which is a simple and industrially scalable manner., Main text with Supplement Material

We report that the strong flux pinning of (Ba,K)Fe2As2 thin films is induced by superconducting phase distribution characteristics. Our thin films present a diverse distribution of the compositional fluctuation, depending on growth conditions. This distribution was achieved by the electron probe microanalyzer elemental mapping and analyzed by the overlay method. The broad transition in magnetic susceptibility indicates that the flux pinning force arises from a distinct range of the concentration of potassium in (Ba,K)Fe2As2 . We compare the activation energy of two different distributions having temperatures of 16780 K and 5027 K at 0.1 T, respectively. The higher activation energy film forms a randomly textured distribution whose stronger pinning potential originates from a rapid spatial $T_{{\rm{c}}}$ change compared to the homogeneous plain film. We conclude that the superconducting phase distribution in the (Ba,K)Fe2As2 film is strongly related to a macroscale vortex interaction, i.e., $\delta T_{{\rm{c}}}$ pinning.

(Ba,K)Fe2As2 superconducting wires have been fabricated by ex-situ powder-in-tube method. In addition to the pure (Ba,K)Fe2As2 wires, silver powder was also used as a chemical addition to improve the performance of these superconducting wires. The transport critical current density (Jc) has reached 1.3×104 A/cm2 at 4.2 K under self field in the wire with Ag addition. The self-field Jc is the highest among all the reported Fe-based superconducting wires so far. We have also performed magneto-optical imaging to this (Ba,K)Fe2As2 superconducting wire with Ag addition, and intragranular Jc of 6.0×104 A/cm2 at 20 K is obtained, which is similar to the estimation from M-H measurement.

In-plane anisotropy of electrical resistivity was studied in samples of the hole-doped ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{K}}_{x}{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$ in the composition range $0.21\ensuremath{\le}x\ensuremath{\le}0.26$ where anisotropy changes sign. Low-temperature ($\ensuremath{\sim}20$ K) irradiation with relativistic 2.5 MeV electrons was used to control the level of disorder and residual resistivity of the samples. Modification of the stress-detwinning technique enabled measurements of the same samples before and after irradiation, leading to the conclusion of anisotropic character of predominantly inelastic scattering processes. Our main finding is that the resistivity anisotropy is of the same sign irrespective of residual resistivity, and remains the same in the orthorhombic ${C}_{2}$ phase above the reentrant tetragonal transition. Unusual $T$-linear dependence of the anisotropy $\mathrm{\ensuremath{\Delta}}\ensuremath{\rho}\ensuremath{\equiv}{\ensuremath{\rho}}_{a}(T)\ensuremath{-}{\ensuremath{\rho}}_{b}(T)$ is found in pristine samples with $x=0.213$ and $x=0.219$, without similar signatures in either ${\ensuremath{\rho}}_{a}(T)$ or ${\ensuremath{\rho}}_{b}(T)$. We show that this feature can be reproduced by a phenomenological model of R. M. Fernandes et al. [Phys. Rev. Lett. 107, 217002 (2011)]. We speculate that onset of fluctuations of nematic order on approaching the instability towards the reentrant tetragonal phase contributes to this unusual dependence.

The compound Ba

Barium-rich silicates were recently found in the lower Cambrian black shale sequence of Anhui Province, South China. The Ba silicates can be divided into Ba-poor K-feldspar, Ba-rich K-feldspar and cymrite, on the basis of occurrence and composition. The Ba-poor K-feldspar have low BaO contents (apfu less than 1.00 and (Al + Si)apfu slightly higher than 4.00. Raman and infrared (IR) spectroscopy has revealed the presence of ${\rm NH}_{\rm 4}^{\rm +} $ and H2O in the Ba-rich K-feldspar, which accounts for the unusual composition of these feldspars. We suggest that the formation processes of the Ba-poor K-feldspar, Ba-rich K-feldspar and cymrite were closely associated with multi-stage hydrothermal fluids enriched in Ba and NH4, consistent with an extensional tectonic setting during the early Cambrian. The Ba-poor K-feldspars might have formed through interactions between pre-existing K-feldspars and hydrothermal fluids. The Ba-rich K-feldspars in mudstone and dolostone formed mainly by precipitation from hydrothermal fluids that infiltrated the sediments, and we suggest the Ba-rich K-feldspars and cymrite in the chert are of exhalative hydrothermal origin.

Perpendicular magnetic anisotropy of the new ferromagnetic semiconductor (Ba,K)(Zn,Mn)$_{2}$As$_{2}$ is studied by angle-dependent x-ray magnetic circular dichroism measurements. The large magnetic anisotropy with the anisotropy field of 0.85 T is deduced by fitting the Stoner-Wohlfarth model to the magnetic-field-angle dependence of the projected magnetic moment. Transverse XMCD spectra highlights the anisotropic distribution of Mn 3$d$ electrons, where the $d_{xz}$ and $d_{yz}$ orbitals are less populated than the $d_{xy}$ state because of the $D_{2d}$ splitting arising from the elongated MnAs$_{4}$ tetrahedra. It is suggested that the magnetic anisotropy originates from the degeneracy lifting of $p$-$d_{xz}$, $d_{yz}$ hybridized states at the Fermi level and resulting energy gain due to spin-orbit coupling when spins are aligned along the $z$ direction.

In-plane anisotropy of electrical resistivity was studied in samples of the hole-doped Ba$_{1-x}$K$_x$Fe$_2$As$_2$ in the composition range $0.21 \leq x \leq 0.26$ where anisotropy changes sign. Low-temperature ($\sim$20~K) irradiation with relativistic 2.5 MeV electrons was used to control the level of disorder and residual resistivity of the samples. Modification of the stress-detwinning technique enabled measurements of the same samples before and after irradiation, leading to conclusion of anisotropic character of predominantly inelastic scattering processes. Our main finding is that the resistivity anisotropy is of the same sign irrespective of residual resistivity, and remains the same in the orthorhombic $C_2$ phase above the re-entrant tetragonal transition. Unusual $T$-linear dependence of the anisotropy $\Delta \rho \equiv \rho_a(T)-\rho_b(T)$ is found in pristine samples with $x=$0.213 and $x=$0.219, without similar signatures in either $\rho_a(T)$ or $\rho_b(T)$. We show that this feature can be reproduced by a phenomenological model of R.~M.~Fernandes {\it et al.} Phys. Rev. Lett. {\bf 107},217002 (2011). We speculate that onset of fluctuations of nematic order on approaching the instability towards the re-entrant tetragonal phase contributes to this unusual dependence.

As-Based Zintl compounds Ba1-xKxCd2As2 crystallized in the CaAl2Si2-type structure (space group P3[combining macron]m1) were prepared using solid-state reactions followed by hot-pressing. We have successfully substituted K for Ba up to x = 0.08, producing hole-carrier doping with concentrations up to 1.60 × 1020 cm-3. We have determined the band-gap value of non-doped BaCd2As2 to be 0.40 eV from the temperature dependence of the electrical resistivity. Both the electrical resistivity and the Seebeck coefficient decrease with hole doping, leading to a power factor value of 1.28 mW m-1 K-2 at 762 K for x = 0.04. A first-principles band calculation shows that the relatively large power factor mainly originates from the two-fold degeneracy of the bands comprising As px,y orbitals and from the anisotropic band structure at the valence-band maximum. The lattice thermal conductivity is suppressed by the K doping to 0.46 W m-1 K-1 at 773 K for x = 0.08, presumably due to randomness. The effect of randomness is compensated by an increase in the electronic thermal conductivity, which keeps the total thermal conductivity approximately constant. In consequence, the dimensionless figure-of-merit ZT reaches a maximum value of 0.81 at 762 K for x = 0.04.

Chemical pressure induced by iso-valent doping has been widely employed to tune physical properties of materials. In this work, we report effects of chemical pressure by substitution of Sb or P into As on a recently discovered diluted magnetic semiconductor (Ba,K)(Zn,Mn)2As2, which has the record of reliable Curie temperature of 230 K due to independent charge and spin doping. Sb and P are substituted into As-site to produce negative and positive chemical pressures, respectively. X-ray diffraction results demonstrate the successful chemical solution of dopants. Magnetic properties of both K-under-doped and K-optimal-doped samples are effectively tuned by Sb- and P-doping. The Hall effect measurements do not show decrease in carrier concentrations upon Sb- and P-doping. Impressively, magnetoresistance is significantly improved from 7% to 27% by only 10% P-doping, successfully extending potential application of (Ba,K)(Zn,Mn)2As2.

We have demonstrated a new description of local electronic structure in the perovskite-like bismuthates Ba1−x K x BiO3 (BKBO) based on existence of the spatially separated Fermi-Bose mixture. We have shown that two types of charge carriers: the local electron pairs (real-space bosons) and the itinerant electrons exist in metallic compound Ba1−x K x BiO3 (x ≥ 0.37). The real-space bosons are responsible for both charge transport in semiconducting BaBiO3 and superconductivity in metallic BKBO, while the fermionic subsystem is responsible for the observed metal-insulator phase transition and appearance of the Fermi-liquid state when the percolation threshold is overcome (x ≥ 0.37). Bosons and fermions occupy different types of the octahedral BiO6 complexes, so they are separated in real space. This scenario fits well into a new quantum state of pair-density wave (PDW), actively discussed for copper-based HTSC.

The effects of high-pressure sintering on the critical current density J c in superconducting wires of (Ba 0.6 K 0.4 )Fe 2 As 2 and (Sr 0.6 K 0.4 )Fe 2 As 2 fabricated by the powder-in-tube technique were studied. The high-pressure sintering was conducted using the hot isostatic pressing (HIP) technique in a pressure up to 120 MPa. Local measurements on the magnetic induction distribution of the wire core in the critical state using magnetooptical imaging demonstrate that a uniform shielding current is flowing and intergranular couplings are very strong. Self-field J c up to 1 × 10 5 A/cm 2 is achieved in wires processed at 120 MPa and 700°C. A systematic measurement of J c in HIP-processed (Ba 0.6 K 0.4 )Fe 2 As 2 wires demonstrates that J c increases steadily with the pressure during the high-pressure sintering. On the other hand, the obtained J c depends sensitively on the temperature during the high-pressure sintering, and the duration of the high-pressure sintering also affects the value of J c .

The recent discovery of superconductivity in ${\mathrm{BaFe}}_{2}{\mathrm{S}}_{3}$ [H. Takahashi et al., Nat. Mater. 14, 1008 (2015)] has stimulated considerable interest in 123-type iron chalcogenides. This material is the first reported iron-based two-leg ladder superconductor, as opposed to the prevailing two-dimensional layered structures of the iron superconductor family. Once the hydrostatic pressure exceeds 11 GPa, ${\mathrm{BaFe}}_{2}{\mathrm{S}}_{3}$ changes from a semiconductor to a superconductor below 24 K. Although previous calculations correctly explained its ground-state magnetic state and electronic structure, the pressure-induced phase transition was not successfully reproduced. In this work, our first-principles calculations show that with increasing pressure the lattice constants as well as local magnetic moments are gradually suppressed, followed by a first-order magnetic transition at a critical pressure, with local magnetic moments dropping to zero suddenly. Our calculations suggest that the self-doping caused by electrons transferred from S to Fe may play a key role in this transition. The development of a nonmagnetic metallic phase at high pressure may pave the way to superconductivity. As extensions of this effort, two other 123-type iron chalcogenides, ${\mathrm{KFe}}_{2}{\mathrm{S}}_{3}$ and ${\mathrm{KFe}}_{2}{\mathrm{Se}}_{3}$, have also been investigated. ${\mathrm{KFe}}_{2}{\mathrm{S}}_{3}$ also displays a first-order transition with increasing pressure, but ${\mathrm{KFe}}_{2}{\mathrm{Se}}_{3}$ shows instead a second-order or weakly first-order transition. The required pressures for ${\mathrm{KFe}}_{2}{\mathrm{S}}_{3}$ and ${\mathrm{KFe}}_{2}{\mathrm{Se}}_{3}$ to quench the magnetism are higher than for ${\mathrm{BaFe}}_{2}{\mathrm{S}}_{3}$. Further experiments could confirm the predicted first-order nature of the transition in ${\mathrm{BaFe}}_{2}{\mathrm{S}}_{3}$ and ${\mathrm{KFe}}_{2}{\mathrm{S}}_{3}$, as well as the possible metallic/superconductivity state in other 123-type iron chalcogenides under high pressure.

Spintronics holds the promise of novel functionality and higher device performance, but a massive challenge is to find semiconducting materials with good electronic properties that are also ferromagnetic. Dilute magnetic semiconductors (DMS) such as Mn-doped GaAs have great potential but are notoriously difficult to make, only stabilizing in thin films in most cases. Recently, a promising new class of DMS materials based on the chemistry and structure of iron-based superconductors has been discovered, including the compound (Ba,K)(Zn,Mn)${}_{2}$As${}_{2}$. These materials can be synthesized in bulk form, providing an unprecedented opportunity to study the mechanism of ferromagnetism in semiconductors. In this work, the authors present detailed temperature-dependent characterization of the atomic and magnetic structure of (Ba,K)(Zn,Mn)${}_{2}$As${}_{2}$ using x-ray and neutron pair distribution function techniques, establishing the existence of an unexpected structural distortion on a short length scale and surprisingly robust short-range ferromagnetic correlations that persist even at room temperature. These results fill in important gaps in the experimental understanding of DMS materials and provide valuable guidance to their theoretical description.

Soon after the discovery of Fe based superconductors, attempts of wire fabrication started using a powder-in-tube (PIT) technique, because their high transition temperature and extremely high upper critical field bring the hope of high field applications. Although the transport critical current density, J c , reported in the early stage was disappointingly low, it has been rapidly improved during the past one year to the orders of 10 4 and 105 A/cm2 by optimizing various processing parameters of the PIT technique. This paper reports one of the works which brought such rapid progress. (Ba,K)Fe2As2 superconducting wires were fabricated by an ex situ powder-in-tube (PIT) process using a melt processed precursor material. The paper also discusses the influence of Ag addition, critical current irreversibility, critical current anisotropy of the tape sample, and finally future prospect in the development of Fe based superconducting wires.

The Co-Ba-K catalysts supported on alumina ceramic substrates were prepared. All the catalysts were characterized by X-ray diffraction and thermogravimetry/differential scanning calorimetry. The catalytic activities were evaluated by a soot oxidation reaction using the temperature-programmed reaction system. The catalytic activities of Co 3 O 4 , Ba(NO 3 ) 2 , Co-Ba, and Co-Ba-K catalysts were studied, and the effect of the contact mode on the soot onset ignition temperature and soot oxidation rate was also discussed. The soot onset ignition temperature is 373 °C for Co-Ba catalysts with molar ratios of 1:2, 1:1 and 2:1, which is the same as that of pure Co 3 O 4 . The Co-Ba catalysts containing KNO 3 can greatly lower the soot onset ignition temperature value. The catalytic activity of pure Co 3 O 4 and Ba(NO 3 ) 2 is affected by catalyst–soot contact intensity. The soot onset ignition temperature is not affected by contact intensity for the catalysts with proper Co-Ba-K ratios. The soot oxidation rate is greatly accelerated when the Co-Ba-K catalysts and soot are in the tight contact mode.

We fabricated (Ba,K)Fe2As2 superconducting wires and tapes using the powder-in-tube method and hot isostatic pressing (HIP). HIP wires and tapes showed a high value of transport critical current density (J c) exceeding 100 kAcm−2 at T = 4.2 K and the self-field. Transport J c in the HIP wire reached 38 kAcm−2 in a high magnetic field of 100 kOe. This value is almost twice larger than the previous highest value of J c among round wires using iron-based superconductors. Enhancement of J c in the wires and tapes was caused by improvement of the drawing process, which caused degradation of the core, formation of microcracks, weak links between grains, and random orientation of grains. Details of the effect of the improved fabrication processes on the J c are discussed.

Dense, crack-free and uniform nanocrystalline La 2−x A x Mo 2 O 9−δ (A = Ca, Sr, Ba, and K; x = 0, 0.05) (LAMOX) films were successfully synthesized on polycrystalline Al 2 O 3 substrates by a modified sol–gel method. Pure LAMOX phases with an average grain size of 200–300 nm were obtained when the annealing temperature was about 650 °C. The cell parameter of nanocrystalline LAMOX films is larger than that of the corresponding microcrystalline samples. The conductivity of the nanocrystalline pure La 2 Mo 2 O 9 film reaches 0.07 S/cm at 600 °C, much higher than that of the corresponding bulk materials. The 2.5%Ca, Sr, Ba, and K-doping can suppress the phase transition occurred at 580 °C in pure La 2 Mo 2 O 9 and enhance the low-temperature ionic conductivity. Furthermore, the activation energy of conductivity in the nanocrystalline La 2 Mo 2 O 9 films decreases to about 0.6 eV in comparison with 1.0 eV in the bulk ones. The increase of unit cell free volume resulted from the intrinsically larger cell parameter of nanocrystalline grains may be mainly responsible for the enhancement of conductivity and decrease of activation energy.

Die Strukturen der bekannten Diindide AIIIn2 (AII = Ca/Sr: hexagonal, Raumgruppe P63/mmc, a = 489.2(2)/500.9(2), c = 773.9(4)/803.6(3) pm, Z = 2, R1 = 0.0254/0.0277, CaGa2-Typ; AII = Ba: orthorhombisch, Raumgruppe Imma, a = 522.0(2), b = 850.4(3), c = 852.0(3) pm, Z = 4, R1 = 0.0265, KHg2-Typ) enthalten In-Tetraederraumnetze als charakteristische Strukturelemente. Gemas der Interpretation als klassische Zintl-Phasen zeigen die berechneten Zustandsdichten Pseudo-Bandlucken. Von den Tetraindiden last sich nur BaIn4 (tetragonal, Raumgruppe I4/mmm, a = 497.0(3), c = 1198.3(3) pm, Z = 2, R1 = 0.0187, BaAl4-Typ) mit dem erweiterten Zintl-Konzept erklaren, die nicht elektronenprazisen isotypen Alkalimetallindide KIn4 und RbIn4 (a = 492.8(3), c = 1257.5(4) pm, R1 = 0.0289) zeigen die strukturellen Auswirkungen einer Depopulation der hochstbesetzten Zustande. Die Monoindide AIn von Ca, Sr und Ba kristallisieren in drei unterschiedlichen neuen Strukturtypen. In CaIn (tetragonal, Raumgruppe I4/mmm, a = 737(2), c = 840.1(12) pm, Z = 8, R1 = 0.0825) liegen isolierte In4-Quadrate vor. SrIn (orthorhombisch, Raumgruppe Fdd2, a = 1023(3), b = 2614(7), c = 840(2) pm, Z = 32, R1 = 0.1185 und BaIn (orthorhombisch, Raumgruppe Cmcm, a = 815.8(4), b = 1248.1(7), c = 557.8(2) pm, Z = 8, R1 = 0.0623) enthalten dagegen in Ubereinstimmung mit dem Zintl-Konzept dreibindige In-Atome, die zu Schichten (SrIn) bzw. Leitern (BaIn) verknupft sind. Beide Verbindungen lassen sich auch strukturell als reduziertes BaIn2 verstehen, ihre Zustandsdichten zeigen wie die der Diindide Pseudo-Bandlucken. Binary Indides AInx (x = 1, 2, 4; A = Ca, Sr, Ba, K, Rb) - Studies on Structural Chemistry and Chemical Bonding The crystal structures of the known diindides AIIIn2 (AII = Ca/Sr: hexagonal, space group P63/mmc, a = 489.2(2)/500.9(2), c = 773.9(4)/803.6(3) pm, Z = 2, R1 = 0.0254/0.0277, CaGa2 type; AII = Ba: orthorhombic, space group Imma, a = 522.0(2), b = 850.4(3), c = 852.0(3) pm, Z = 4, R1 = 0.0265, KHg2 type) contain 3D In tetrahedral networks. In accordance with their interpretation as classical Zintl compounds, the calculated density of states show pseudo band gaps. Among the tetraindides only BaIn4 (tetragonal, space group I4/mmm, a = 497.0(3), c = 1198.3(3) pm, Z = 2, R1 = 0.0187, BaAl4 type) can be explained with the extended Zintl concept; the electron deficient isotypic alkaline metal indides KIn4 and RbIn4 (a = 492.8(3), c = 1257.5(4) pm, R1 = 0.0289) show the structural consequences of the depopulation of the highest occupied states. The monoindides AIn of Ca, Sr und Ba crystallize with three different new structure types: In CaIn (tetragonal, space group I4/mmm, a = 737(2), c = 840.1(12) pm, Z = 8, R1 = 0.0825) isolated squares In4 are present. In contrast, SrIn (orthorhombic, space group Fdd2, a = 1023(3), b = 2614(7), c = 840(2) pm, Z = 32, R1 = 0.1185 and BaIn (orthorhombic, space group Cmcm, a = 815.8(4), b = 1248.1(7), c = 557.8(2) pm, Z = 8, R1 = 0.0623) show - in accordance with the Zintl counting rules - three bonded In2- atoms, which are connected to form layers (SrIn) and ladders (BaIn) respectively. Both compounds can be structurally regarded as reduced BaIn2, their total density of states like those of the diindide, exhibit pseudo band gaps.

(Ba,K)-feldspars occur with cymrite as thin layers of massive fine-grained celsian interbedded with apatite, sulfides and barite, or diseminated in the thin-bedded barite-bearing siliceous and carbonate beds ranging in thickness from 0.15 to 0.40 m in three barite deposits in Zamora, Spain. The (Ba,K)-feldspars, which include celsian, hyalophane and K-feldspar, vary from 1.3 t o 96.4 mole % BaAl2Si2O8, but exhibit two discontinuities, at 8–24 and 40–92 mol.%. The associated cymrite shows 1.3–3 mol.% KAlSi3O8 in solid solution. Relict celsian has a similar K content, 1.2–2.8 mol.% KAlSi 3O8. The Ba-rich feldspars may have been deposited i) as an authigenic phase, or ii) by replacement of authigenic barite during a later diagenetic or metamorphic event. Cymrite and celsian were formed under low-grade dynamothermal metamorphism that affected Paleozoic sedex barite deposits of Zamora. Fluid-inclusion studies indicate 350 °–370°C and 1.5 kbars as conditions of equilibration. Those data, and the presence of vitrinite (350°C), indicate the upper limit of P–T reached. These conditions are close to the reaction curve for celsian + H 2O = cymrite. The stability field of cymrite confirms that this mineral can be stable in low-P – low-T metasedimentary environments. That reaction has geobarometric and tectonothermal importance.

We report the iron isotope effect on a transition temperature ( T c ) in an optimally-doped (Ba,K)Fe 2 As 2 ( T c = 38 K) and SmFeAsO 1− y ( T c = 54 K) superconductors. In order to obtain the reliable isotope shift in T c , twin samples with different iron isotope mass are synthesized in the same conditions (simultaneously) under high-pressure. We have found that (Ba,K)Fe 2 As 2 shows an inverse iron isotope effect α Fe = −0.18 ± 0.03 while SmFeAsO 1− y shows a small iron isotope effect α Fe = −0.02 ± 0.01, where the isotope exponent α is defined by T c ∼ M − α ( M is the isotopic mass). The results show that α Fe changes in the iron-based superconductors depending on the system. The distinct iron isotope effects imply the exotic coupling mechanism in the iron-based superconductors.

Surkhobite, a new mineral related to the members of the jinshajiangite-perraultite series, was approved in 2002 (IMA No. 2002-037) and later discredited (IMA decision 06-E). It is redefined here with a new formula and revalidated with the original name (IMA 07-A). It occurs as platy crystals up to 1 mm and grains up to 2 × 1 × 0.4 cm in the association with aegirine, microcline, albite, quartz, amphibole, annite, bafertisite, astrophyllite, zircon, fluorite, polylithionite, stillwelite, sogdianite, tadjikite in alkaline pegmatite at the massif Dara-i-Pioz, Tajikistan. Surkhobite is translucent, brownish-red, lustre vitreous, streak white, cleavage perfect on {001}; hardness is anisotropic: the minimum value H 1 = 250 kg/mm 2 , the maximum value H 2 = 482 kg/mm 2 ; Mohs’ hardness is 4½. Biaxial, negative, β= 1.858(10), γ= 1.888(10); 2 V = 65(5)°; α= 1.790 (calculated from 2 V ). Optical orientation: X = b , Z ∧ a = 34°. Dispersion is strong, r . Pleochroism: Y (orange) > Z (bright-yellow) ≥ X (yellow). Microtwinning on (001) is observed. D calc = 3.98 g/cm 3 ; D meas = 3.84(10) g/cm 3 . IR and Mossbauer spectra are given. Chemical composition is (electron microprobe combined with Mossbauer data, wt.%): Na 2 O 2.27, K 2 O 1.87, CaO 2.53, SrO 0.26, BaO 11.16, MgO 0.13, MnO 16.32, FeO 13.92, Fe 2 O 3 2.11, Al 2 O 3 0.02, SiO 2 27.17, TiO 2 16.14, Nb 2 O 5 2.14, ZrO 2 0.34, F 2.94, H 2 O (by Penfield method) 1.17, -O=F 2 –1.24, total 99.25. The empirical formula is ( Z = 2): Na 2.60 K 1.41 Ca 1.60 Sr 0.09 Ba 2.58 (Mn 8.17 Fe 2+ 6.88 Fe 3+ 0.94 Mg0. 115 Al 0.01 ) ∑16.115 (Ti 7.17 Nb 0.57 Zr 0.10 ) ∑7.84 Si 16.06 H 4.61 F 5.49 O 70.51 . The simplified formula, taking into account the crystal structure, is ( Z = 2): KBa 3 Ca 2 Na 2 (Mn, Fe 2+ , Fe 3+ ) 16 Ti 8 (Si 2 O 7 ) 8 O 8 (OH) 4 (F,O,OH) 8 . The crystal structure was refined on a single crystal to R = 0.043 with 3686 independent reflections ( F > 2σ). Surkhobite is monoclinic, C 2, a = 10.723(1), b = 13.826(2), c = 20.791(4) A, β = 95.00(1)°. Surkhobite is the Mn-dominant analogue of jinshajiangite and differs from perraultite in that Ca is ordered onto and is dominant in the site A (6). The strongest lines of the powder difraction pattern [ d , A ( I , %) ( hkl )] are: 10.39 (20) (002), 3.454 (100) (006), 3.186 (15) (321), 2.862 (15) (225), 2.592 (70) (008), 2.074 (40) (048).

The valences of Bi and O in superconducting Ba-K-Bi-O and Ba-K-M-Bi-O (M = Rb, La, Eu, In, Tl and Pb) and the related compounds NaBa 3 BiO 6 , Li 6 KBiO 6 , Bi 2 O 3 and BaO 2 were determined using XPS. The results show that there is no evidence for the existence of Bi 5+ in superconducting Ba-K-Bi-O and Ba-K-M-Bi-O, instead, there is evidence for the presence of charge separation: Bi 3+ and Bi (3+) −δ. Besides, the 01s XPS results suggest that some of the lattice oxygen are not in the normal 0 2- state but rather probably have a configuration consistent with 0 1- or 0 2- 2 .

Bi0.9−x Ba0.1K x FeO3 (x = 0, 0.01, 0.02) nanoparticles have been successfully prepared using sol–gel method. X-ray diffraction data revealed rhombohedral distorted perovskite structure for all samples. The magnetization and the leakage current density both increased with K doping. Space charge limited conduction was found to be the dominant mechanism in whole electric field for all the samples investigated by plotting log J versus log E. In addition, the band gaps of all nanoparticles were investigated and the values showed no obvious change with the increase of K content due to the interplay of oxygen vacancies and bond angle of Fe–O–Fe. The dielectric properties including the dielectric constant and loss were also investigated.

Grain size and piezoelectric properties were investigated in (K, Na)NbO3 ceramics substituted with Ba for K and Na by 1 to 5 mol%, in anticipation of high piezoelectric properties. The grain size strongly depended on the A/B ratio in perovskite structure. The grain growth phenomenon was markedly similar to that of BaTiO3 semiconducting ceramics with donor additives. Piezoelectric properties were strongly affected by grain size. MnO additive was added to suppress grain growth anomaly, dense ceramic body formation and withstanding voltage enhancement. However, a manufacturing process, in which MnCO3 was directly mixed to other raw material powders, resulted in the formation of large pores ranging to 1 mm diameter in their ceramic bodies. The powder obtained by previously calcining the mixture of Nb2O5 and MnCO3 was used as a raw material for MnO addition, in order to prevent the formation of large pores. By adding 0.5 mol% MnO, grain growth anomaly was inhibited, and a uniform and dense ceramic body was consequently obtained without piezoelectric property degradation.

The perovskites La 0.8 A 0.2 MnO 3 (A=Sr, Ba, K, Cs) and LaMn 0.8 B 0.2 O 3 (B=Ni, Zn, Cu) were studied as catalysts for the oxidation of lean mixtures of hydrogen or propene in the temperature range of 200–450°C (hydrogen) and 150–550°C (propene), respectively. The catalytic features were correlated with the redox behavior of the oxides as revealed by temperature-programmed reduction (TPR) experiments. The highest activity for hydrogen oxidation was found over strontium, barium and copper substituted manganites, whereas in the case of propene oxidation the copper substituted perovskite showed substantially lower activity, which was assigned to the stronger bonding of the produced carbon dioxide to the copper centers. The results are discussed with regard to the concepts of suprafacial and intrafacial catalysis. Apart from the temperature control, the occurrence of one or another of the two mechanisms is imposed by the nature of the substituted cation.

The selective catalytic reduction of nitrogen oxides in the presence of oxygen and water vapor was investigated over perovskite-type mixed oxides La 0.8 A 0.2 MnO 3 (A=Sr, Ba, K, Cs) and LaMn 0.8 B 0.2 O 3 (B=Ni, Zn, Cu) with propene as the reductant, in the temperature range of 150–550°C. The catalysts were contacted with a reactant mixture containing 1000 ppm NO, 500 ppm C 3 H 6 , 5% O 2 and 5% H 2 O in helium at a space velocity of 14.4 cm 3 /g s. A maximum was observed in the conversion of nitrogen oxides to nitrogen with temperature in the range of 300–400°C. In the absence of propene, the activity of these perovskites for NO removal in the 300–550°C range increased from approximately 20% (with propene) to 40% (without propene). Water inhibited the NO x removal process as well, the conversion levels in the propene and water-free gas mixtures rising to about 50–55%. The removal of nitrogen oxides did not take place in the absence of oxygen. Two different reaction mechanisms were postulated: (i) the selective reduction with propene at 150–300°C; (ii) the direct decomposition, which is inhibited by the presence of propene and water, at 300–550°C. The nitrogen dioxide formed by the perovskite-catalyzed oxidation of nitrogen monoxide appears to play a key role in both mechanisms.

Currently available investigations of the isotope effect in Fe-based superconductors are all based on macroscopic resistivity and susceptibility measurements and results are highly controversial. Here we present an investigation of the Fe isotope effect in the (Ba, K)Fe2As2 superconductor by temperature-dependent EXAFS in the framework of Einstein model. This method separates the static structural isotope contribution and the local lattice isotope contribution. Results point out the isotope substitution has a negligible effect on inter-atomic distances. On the contrary, both the local vibrations of the Fe-As and the Fe-Fe bonds show strong iron isotope dependence, which is a marker of an “intrinsic” isotope effect. This bulk iron isotope contribution to the local lattice dynamics suggests the local phonons play an important role in the (Ba, K)Fe2As2 superconductor and a three-dimensional electron-phonon interaction should be considered to understand the superconducting mechanism of iron-based superconductors.

用ＸＰＳ和ＸＲＤ表征了Ｂａ－Ｋ－Ｂｉ－Ｏ超导体熔盐电结晶的阳极和阴 极产物，用ＳＥＭ分析了Ｂａ－Ｋ－Ｂｉ－Ｏ单生长形态。结果表明，阳极产物是Ｂａ－Ｋ－Ｂｉ－Ｏ超导体单晶，以台阶式方式生长。－Ｋ－Ｂ－

Systematic high resolution angle-resolved photoemission spectroscopic studies have been performed on the optimally electron-doped BaFe1.82Co0.18As2 (Tc=24 K) and hole-doped Ba0.6K0.4Fe2As2 (Tc=37 K) superconductors. The superconducting gap is nearly isotropic in momentum space. Utilizing different experimental geometries, the detailed electronic band structures were determined experimentally and compared with first principle LDA calculations. The overall bandwidth is reduced by a factor of 2. However, the low energy quasiparticle dispersions near zone corner exhibit stronger renormalization by a factor of 4–5. kz dependence was observed on the electron pockets at zone corner.

The composition of pulsed-laser-deposited Y-Ba-Cu-O and Ba-K-Bi-O thin films is shown to be strongly affected by target conditioning, gas pressure, and target-substrate distance. For both compounds, ablation from a freshly sanded target surface results in films with an excess of the more volatile elements. The concentration of these volatile elements in the films decreases until the system reaches a steady state after sufficient ablation from the target. Y-Ba-Cu-O film composition is also affected by oxygen pressure and target-substrate distance. Increasing pressure or distance results in relative copper and barium depletion in the central region of deposition, presumably due to differences in the efficacy of oxygen in scattering the different elements. This relationship between pressure, distance, and composition is shown to be significant for the growth of optimal superconducting Y-Ba-Cu-O thin films. The composition of Ba-K-Bi-O is also affected strongly by background gas pressure. Ba-K-Bi-O deposited in vacuum is potassium deficient in the film center. A background argon pressure of 1 Torr, however, increases the potassium concentration and results in films with uniform composition over a broad area. We argue that this effect is significant in explaining a successful growth method for superconducting Ba-K-Bi-O films.

Temperature-dependent X-ray absorption investigations were made on the Bi L 3 -edge in Ba 1~x K x BiO 3 with x"0.0 h, 0.4 and 0.5. For the superconducting samples (x"0.4 and 0.5) it has been found that the local structure di!ers from the ideal cubic in contrast to the neutron and X-ray di!raction data. The provided analysis of the EXAFS spectra indicates that the oxygen atoms move in double-well potential produced by the existence of two non-equivalent octahedral types of the oxygen environment of bismuth. The vibrations in such a potential lead to modulations of the Bi}O lengths with low frequency which is determined by the soft oxygen octahedron rotation mode frequency. This induces strong electron}phonon interaction and may be the reason for relatively high-temperature transition („ # &30 K) to the superconducting state. ( 2000 Elsevier Science B.V. All rights reserved.

We report that the (Ba,K)Fe2As2 crystal with Tc =3 2 K shows a pinning potential, U0, as high as 104 K, with U0 showing very little field dependence. The (Ba,K)Fe2As2 single crystals become isotropic at low temperatures and high magnetic fields, resulting in a very rigid vortex lattice, even in fields very close to Hc2. The isotropic rigid vortices observed in the two-dimensional (2D) (Ba,K)Fe2As2 distinguish this compound from 2D high-Tc cuprate superconductors with 2D vortices. The vortex avalanches were also observed at low temperatures in the (Ba,K)Fe2As2 crystal. It is proposed that it is the K substitution that induces both almost isotropic superconductivity and the very strong intrinsic pinning in the (Ba,K)Fe2As2 crystal.

We report that single crystals of (Ba,K)Fe2As2 with Tc = 32 K have a pinning potential, U0, as high as 10^4 K, with U0 showing very little field depend-ence. In addition, the (Ba,K)Fe2As2 single crystals become isotropic at low temperatures and high magnetic fields, resulting in a very rigid vortex lattice, even in fields very close to Hc2. The rigid vortices in the two dimensional (Ba,K)Fe2As2 distinguish this compound from 2D high Tc cuprate superconductors with 2D vortices, and make it being capable of cearrying very high critical current.Flux jumping due to high Jc was also observed in large samples at low temperatures., Comment: 4 pages, 7 figures. submitted

We have succeeded in preparing the well-crystallized polycrystalline samples of Ba0.64(K1−xRbx)0.36BiO3 in a single process using molten KOH/NaOH eutectic mixture at a temperature as low as 270 °C. The value of Tc ∼ 30 K is almost independent on the Rb content x.

We found that the transport Jc of the ex-situ PIT processed (Ba,K)Fe2As2 (Ba-122) wire with single Ag sheath can be significantly enhanced by repeating the combined process of rolling and heat treatment. The transport Jc (4.2 K and 10 T) of 4.4 x 103 A/cm2 (Ic =15.7 A) was obtained for a thin tape of 0.3 mm in thickness, which is the highest value reported so far for the PIT processed 122 wires and tapes with a Ag sheath and processed by a conventional route. The measurement by a hybrid magnet showed that Jc-H curve maintains very small field dependence up to the strong magnetic field of 28 T as expected from the previously reported high Hc2 value. The core of the thin tape shows dense grain structure with less cracks and voids and indicates the development of c-axis alignment, although it is still incomplete. The researches to elucidate the origin of Jc enhancement and to have further improvement of transport Jc are now ongoing. The process is simple using a Ag single sheath and, therefore, more realistic technique for long length wire production., Comment: 8 pages, 7 figures

The extent of the vortex-liquid state in underdoped single crystals of the oxypnictide superconductors NdFeAs(O,F) and (Ba,K)Fe2As2 is investigated using specific heat (C-p) and Hall-probe magnetization experiments. In both materials, the vortex liquid lies entirely in the regime where the three-dimensional lowest Landau-level (3D-LLL) approximation is valid and both systems present a very small shift in the specific heat anomaly with increasing field. The irreversibility line, defined as the onset of diamagnetic response, is very rapidly shifted toward lower temperatures in NdFeAs(O,F) but remains close to the C-p anomaly in (Ba,K)Fe2As2. These measurements strongly suggest that a vortex-liquid phase occupies a large portion of the mixed-state phase diagram of NdFeAs(O,F) but not in (Ba,K)Fe2As2. This difference can be attributed to different Ginzburg numbers Gi, the latter being about 100 times larger in NdFeAs(O,F) than in (Ba,K)Fe2As2. The angular dependence of the upper critical field, derived from 3D-LLL scaling of the irreversibility lines, presents deviations from the standard 3D effective-mass model in both materials with an anisotropy being about three times smaller in (Ba,K)Fe2As2 (gamma similar to 2.5) than in Nd(F,O)FeAs (gamma similar to 7.5).

Instead of ordinal pure Ag, Ag-based Sn binary alloys (up to 7.5 at%Sn) with higher mechanical strength are used for the sheath material of ex situ powder-in-tube (PIT)-processed (Ba,K)Fe2As2(Ba-122) tapes. We found that the use of the Ag-Sn alloy enhances the densification and texturing of the Ba-122 core, resulting in higher transport, J c. Moreover, the optimum heat treatment temperature for a high J c can be lowered by around 100 °C due to the higher packing density of the Ba-122 core prior to the final heat treatment. We also found that the smoothness of the interface between the sheath and Ba-122 core is significantly improved by using the Ag-Sn binary alloy sheaths. These results show that the Ag-Sn alloy is promising as a sheath material in PIT-processed Ba-122 superconducting wires.