A safe, simple and easily scaleable one-step sintering method is proposed to fabricate newly discovered superconductors of SmO1-xFxFeAs. Superconducting transition with the onset temperature of 54.6 K and high critical fields Hc2(0) >=200 T were confirmed in SmO1-xFxFeAs with x = 0.3. At 5 K and self field, critical current density Jc estimated from the magnetization hysteresis using the whole sample size and the average particle size reached 8.5x10^3 and 1.2x10^6 A/cm^2, respectively. Moreover, the Jc exhibited a very weak dependence on magnetic field. Microstructural characterizations revealed that the whole sample Jc improvement could be achieved by either perfect texture or optimization of fabrication process in this strongly-layered superconductor. Our results clearly demonstrated that one-step synthesis technique is unique and versatile and hence can be tailored easily for other rare earth derivatives of REFeAsO superconductors.
We report on the synthesis and microstructural studies of fluorine based iron doped superconductors. We have successfully synthesized the fluorine based new superconducting material LaO1-xFxFeAs by choosing comparatively lower temperature and longer synthesis duration. The superconducting transition temperature that we have achieved is 27.5 K which is observed at doping level of x=0.2. The structural microstructural characterizations have been done by employing XRD, SEM and TEM techniques. The SEM and TEM micrographs reveal the layered structure.
We present data of multi harmonic magneto-dynamic experiments. In particular, we performed ac magnetic susceptibility experiments on layered pnictide-oxide quaternary compound NdOFeAs doped with fluorine. The experiments allow measure the critical temperature and probe the flux dynamic behavior using the third harmonic component of the ac susceptibility of a NdF0.16FeAsO0.84 bulk sample as a function of temperature and frequency of the applied ac magnetic fields. Measured signals are connected with the non-linear superconducting flux dynamic behavior and are characterized by a flux critical st…
We report on the synthesis and structural/ microstructural studies of iron based fluorine doped LaOFeAs superconductors. We have successfully synthesized fluorine doped superconducting LaO1-xFxFeAs materials by choosing lower temperature (1150^0C) and longer synthesis duration (60 hours) as compared to the standard values of these employed in the pioneering first contribution [Kamihara et al 2008 J Am Chem Soc 130 3296]. Decrease of lattice parameters as determined by x-ray diffraction confirm the substitution of fluorine. The superconducting transition temperature is 27.5 K which is observed …
We demonstrate that Ta sheathed SmO1-xFxFeAs wires were successfully fabricated by the powder-in-tube (PIT) method for the first time. Structural analysis by mean of x-ray diffraction shows that the main phase of SmO1-xFxFeAs was obtained by this synthesis method. The transition temperature of the SmO0.65F0.35FeAs wires was confirmed to be as high as 52 K. Based on magnetization measurements, it is found that a globe current can flow on macroscopic sample dimensions with Jc of ~3.9x10^3 A/cm^2 at 5 K and self field, while a high Jc about 2x10^5 A/cm^2 is observed within the grains, suggesting …
A series of polycrystalline SmO1-xFxFeAs bulks (x=0.15, 0.2, 0.3 and 0.4) were prepared by the conventional solid state reaction. Resistivity, susceptibility, magnetic hysteresis, critical current density and microstructure of these samples have been investigated. It is found that critical transition temperature Tc increases steadily with increasing fluorine content, with the highest onset Tc=53 K at x=0.4. On the other hand, the superconductivity seems correlated with lattice constants; that is, Tc rises with the shrinkage of a-axis while resistivity increases with the enlargement of c-axis. …
We succeeded in the synthesis of high-Jc MgB2 bulks via high energy ball-milling of elemental Mg and B powder at ambient temperatures. Alternatively to longtime mechanical alloying technique, the mixed powder was ball-milled for only 1h and the completed reaction is achieved by subsequent annealing. The correlations among synthesis parameters, microstructures and superconducting properties in MgB2 bulks were investigated. Samples were characterized by XRD and SEM, and the magnetization properties were examined in a SQUID magnetometer. The high- Jc, approximately 1.7*106A/cm2(15K, 0.59T), and i…
We study the effect of synthesis temperature on the phase formation in nano(n)-SiC added bulk MgB2 superconductor. In particular we study: lattice parameters, amount of carbon (C) substitution, microstructure, critical temperature (Tc), irreversibility field (Hirr), critical current density (Jc), upper critical field (Hc2) and flux pinning. Samples of MgB2+(n-SiC)x with x=0.0, 0.05 & 0.10 were prepared at four different synthesis temperatures i.e. 850, 800, 750, and 700oC with the same heating rate as 10oC/min. We found 750oC as the optimal synthesis temperature for n-SiC doping in bulk MgB2 i…
High-pressure (HP) synthesis and sintering are promising methods for manufacturing of the bulk MgB2 superconductive material. The available high-pressure apparatuses with 100 cm3 working volume can allow us to use the bulk MgB2 for practical applications such as electromotors, fly-wheels, bearings, etc. We have found that the Ta presence during HP synthesis (especially) or sintering process (in the form of a foil that covered the sample and as an addition of Ta powder of about 2-10 wt.% to the starting mixture of B and Mg or to MgB2 powder) increases the critical current density (jc) in the ma…
The iron-based superconductor FeTe$_{1-x}$Se$_{x}$ has attracted considerable attention as a candidate topological superconductor owing to a unique combination of topological surface states and bulk high-temperature superconductivity. The superconducting properties of as-grown single crystals, however, are highly variable and synthesis dependent due to excess interstitial iron impurities incorporated during growth. Here we report a novel physicochemical process for pumping this interstitial iron out of the FeTe$_{1-x}$Se$_{x}$ matrix and achieving bulk superconductivity. Our method should have…
Here, we report the successful synthesis of electron- (Ni) and hole- (K) doped bulk BaFe2As2 compounds by means of mechanical alloying (MA) process. The MA technique allows one to obtain amorphous phase BaFe2As2 with a homogeneous distribution of doping atoms at room temperature without continuous heating. We found the optimum time for high-energy milling is in the range between 1-1.5 hours. Using pre-synthesised FeAs and NiAs precursors, we successfully obtained BaFe2-xNixAs2 and Ba1-xKxFe2As2 superconducting bulk samples after short-range heat treatment. This method can be easily scaled acco…
Exploratory synthesis efforts for iron-based superconductors (FeSC) have been driven by hopes of improving superconducting critical temperatures (TCs), providing high-quality samples for in-depth studies of intrinsic properties, and exploring potential superconductivity in similar families of materials. This manuscript summarizes the synthesis routes that are used for producing FeSC and their undoped parents, in single crystal and polycrystalline forms. A few of the materials challenges are summarized.
Superconductivity has been realized in films of La$_{1-x}$Sr$_x$NiO$_2$. Here we report synthesis and characterization of polycrystalline samples of La$_{1-x}$Sr$_x$NiO$_3$ and La$_{1-x}$Sr$_x$NiO$_2$ ($0\le x\le 0.2$). Magnetization and resistivity measurements reveal that La$_{1-x}$Sr$_x$NiO$_3$ are paramagnetic metals and La$_{1-x}$Sr$_x$NiO$_2$ exhibit insulating behavior. Superconductivity is not detected in bulk samples of La$_{1-x}$Sr$_x$NiO$_2$. The absence of superconductivity in bulk La$_{1-x}$Sr$_x$NiO$_2$ may be due to the generation of hydroxide during reduction or a small amount …
The lanthanum copper oxide, La2CuO4, which is an end member of the prototype high-Tc superconductors (La,Sr)2CuO4 and (La,Ba)2CuO4, crystallizes in the "K2NiF4" structure in high-temperature bulk synthesis. The crystal chemistry, however, predicts that La2CuO4 is at the borderline of the K2NiF4 stability and that it can crystallize in the Nd2CuO4 structure at low synthesis temperatures. In this article we demonstrate that low-temperature thin-film synthesis actually crystallizes La2CuO4 in the Nd2CuO4 structure. We also show that the phase control of "K2NiF4"-type La2CuO4 versus "Nd2CuO4"-type…
We report synthesis and superconductivity at 3.7K in PrO0.5F0.5BiS2. The newly discovered material belongs to the layered sulfide based REO0.5F0.5BiS2 compounds having ZrCuSiAs type structure. The bulk polycrystalline compound is synthesized by vacuum encapsulation technique at 7800C in single step. Detailed structural analysis has shown that the as synthesized PrO0.5F0.5BiS2 is crystallized in tetragonal P4/nmm space group with lattice parameters a = 4.015(5) Å, c = 13.362(4) Å. Bulk superconductivity is observed in PrO0.5F0.5BiS2 below 4K from magnetic and transport measurements. Electrical …
Superconducting properties of bulk, dense, pure MgB2 and doped (Mg1-xAx)B2 samples with A = Na, Ca, Cu, Ag, Zn and Al were studied for compositional ranges 0 < x < 0.20. The effect on pinning properties and critical current were investigated, particularly for A = aluminium. The samples were sintered and/or synthesised at high pressure - high temperature in a cubic multi-anvils press (typically : 3.5-6 GPa, 900-1000C). They were characterised by x-ray diffraction, scanning electron microscopy and their superconducting properties were investigated by a.c. susceptibility, magnetisation (VSM and S…
The sound velocity is measured in polycrystalline MgB2 synthesized from the elements, and the bulk modulus and the Debye temperature are calculated. The conversion of an elastic wave into electromagnetic radiation is investigated in the mixed state.The dynamic parameters of the vortex lattice are estimated. This paper was published in Low Temp. Rhys., 2002, v.28, N3, p.270-274
Polycrystalline samples and submillimeter size single crystals of Na-doped Ca2CuO2Cl2 have been synthesized under high pressure. A series of experiments showed that the Na content depends not only on the pressure during the synthesis but also on the synthesis temperature and time. From a comparison of the Na-CCOC data with those of structurally related La214 cuprate superconductors we concluded that chlorine at the apical site is less effective that oxygen in supplying charge carriers to the CuO2 plans. As a result, the coupling between the CuO2 planes is weakened, the transition temperature T…
We have synthesized the single-phase polycrystalline samples of Sn1-xAgxTe, Ag-doped topological crystalline insulator SnTe, with a range of x = 0-0.5 using a high-pressure synthesis method. The crystal structure of Sn1-xAgxTe at room temperature is a cubic NaCl-type structure, which does not vary upon Ag substitution. Bulk superconductivity with a transition temperature of 2.4 K was observed for x = 0.15-0.25, and the optimal Ag content was x = 0.2. The Sn1-xAgxTe superconducting phase will be useful for understanding the superconductivity nature and mechanisms of the carrier-doped SnTe syste…
We report the synthesis of single phase Bi3O2S3 sample and confirm the occurrence of bulk superconductivity with transition temperature at 5.8 K. The Bi3O2S3 super-conductor is categorized as the typical type-II supercon-ductor based on the results of both temperature and mag-netic field dependences of magnetization. Hall coefficient measurements give evidence of a multiband character, with a dominant conduction mainly by electron-like charge carriers. The charge carrier density is about 1.45 X 1019 cm3, suggesting that the system has very low charge carrier density.
We have synthesized bulk Mg(B$_{1-x}$C$_x$)$_2$ from a mixture of elemental Mg, B, and the binary compound B$_4$C. Carbon incorporation was dramatically improved by a two step reaction process at an elevated temperature of 1200 $^o$C. This reaction process results in a solubility limit near x$\sim$0.07. We found that impurities in the starting B cause an additive suppression of T$_c$. We combine these data with T$_c$ and H$_{c2}$(T=0) data from CVD wires as well as plasma spray synthesized powders and present a unifying H$_{c2}$ and T$_c$ versus x plot.
Heterogeneous sonochemical method was applied for synthesis of novel superconducting nanocomposites consisting of magnetic (and/or nonmagnetic) nanoparticles embedded into the bulk of ceramic superconductors. In addition to in-situ production of the efficient pinning centers, this synthesis method considerably improves the interbrain coupling. Significant enhancement of the magnetic irreversibility is reported for Fe2O3 nanoparticles embedded into the bulk of MgB2 superconductor. Nonmagnetic Mo2O5 nanoparticles also increase pinning strength, but less than magnetic Fe2O3. Detailed magnetizatio…
BaFe2As2 (Ba-122) and (Ba0.6K0.4)Fe2As2 (K-doped Ba-122) powders were successfully synthesized from the elements using a reaction method, which incorporates a mechanochemical reaction using high-impact ball milling. Mechanically-activated, self-sustaining reactions (MSR) were observed while milling the elements together to form these compounds. After the MSR, the Ba-122 phase had formed, the powder had an average grain size < 1 μm, and the material was effectively mixed. X-ray diffraction confirmed Ba-122 was the primary phase present after milling. Heat treatment of the K-doped MSR powder at …
Bulk MgB2 samples were prepared under different synthesis conditions and analyzed by scanning and transmission electron microscopy. The critical current densities were determined from the magnetization versus magnetic field curves of bulk and powder-dispersed-in-epoxy samples. Results show that through a slow cooling process, the oxygen dissolved in bulk MgB2 at high synthesis temperatures can segregate and form nanometer-sized coherent precipitates of Mg(B,O)2 in the MgB2 matrix. Magnetization measurements indicate that these precipitates act as effective flux pinning centers and therefore si…
Bulk polycrystalline NbC samples are synthesized through solid state reaction route in an evacuated sealed quartz tube. Studied NbC samples are crystallized in NaCl-type cubic structure with space group Fm-3m. To control cell parameters and minute un-reacted phases, different samples are synthesized with various heat treatments. Finally phase pure NbC is achieved. The grain size of the as systemized material being seen from SEM (scanning electron microscopy) is non-uniform of around 3-10μm size. Crystal structure and lattice parameters of samples have been calculated by Rietveld analysis of ro…
One of the most important properties of very recently reported FeSe based superconductors is the robustness of their superconductivity under applied magnetic field. The synthesis and control of superconductivity in FeSe based compounds is rather a difficult task. Synthesis and physical property characterization for optimized superconductivity of FeSe1/2Te1/2 at 13 K is reported here. The compound crystallized in a tetragonal structure with lattice parameters a = 3.8008(10) and c = 6.0187 (15) A. Magnetization measurements indicated bulk superconductivity with lower critical field (Hc1) of arou…
Enhancement of the superconducting transition temperature in Mn-doped CaKFe4As4 processed by the high gas-pressure and high-temperature synthesis method
Compounds of Sr1-xLaxFe2As2 were synthesized by solid state reaction at 1273 K, under pressures of 2 or 3 GPa. The Sr1-xLaxFe2As2 phase was dominant up to x = 0.5, and superconductivity was observed at $x \ge 0.2$. A maximum critical temperature Tc of 22 K, and a maximum shielding volume fraction of ~70 % were obtained at x = 0.4. This is the first experimental demonstration of electron-doped superconductivity in 122-type iron pnictides, where electrons were doped through aliovalent substitution at the site of the alkaline earth metal. The optimal Tc was slightly higher than that for the Co-do…
We have prepared powder samples of NaxCoO2 x yH2O using a new synthesis route. Superconductivity was observed in Na0.3CoO2 x 1.3H2O between 4 and 5K as indicated by the magnetic susceptibility. The bulk compressibilities of Na0.3CoO2 x 1.3H2O, Na0.3CoO2 x 0.6H2O and Na0.3CoO2 were determined using a diamond anvil cell and synchrotron powder diffraction. Chemical changes occurring under pressure when using different pressure transmitting media are discussed and further transport measurements are advocated.
The iron oxyarsenide TbFeAsO0.85 was synthesized by a high-pressure method. A high-quality polycrystalline sample was obtained and characterized by measurements of magnetic susceptibility and electrical resistivity. Bulk superconductivity with Tc of 42 K was clearly established without an F doping usually conducted to tune on superconductivity in the iron oxypnictide.
Superconductors comprising 5d transition metals of Ir and Pt have been widely explored because they have the potential of unique superconductivity caused by the strong spin-orbit interaction (SOI). We successfully synthesized BaIr2, the last Laves phase remaining unsynthesized in the MgCu2-type AM2 (A = Ca, Sr, Ba; M = Rh, Pd, Ir, Pt). BaIr2 was crystallized at 925 C under a pressure of 3.3 GPa via a solid-state reaction between Ba and Ir powders; it was found to have the longest a-lattice constant of 8.038(1) A among AM2. BaIr2 exhibited bulk superconductivity at a transition temperature (Tc)…
Using the apical oxygen doping mechanism, i.e. a partial substitution of divalence O for the monovalence Cl, a p-type oxychloride cuprate superconductor, Sr2CuO2+xCl2-y, was synthesized at high pressure high temperature. The x-ray diffraction refinement suggests the superconductor crystallizes into a 0201 structure with space group I4/mmm and lattice parameters being a=3.92A, c=15.6 A. The magnetic susceptibility as well as resistance measurements indicated that the bulk superconductivity with transition temperature 30K was achieved in the sample.
Intercalation of organic cations in superconducting iron selenide can significantly increase the critical temperature (Tc). We present an electrochemical method using beta-FeSe crystals (Tc ~ 8 K) floating on a mercury cathode to intercalate tetramethylammonium ions (TMA+) quantitatively to obtain bulk samples of (TMA)0.5Fe2Se2 with Tc = 43 K. The layered crystal structure is closely related to the ThCr2Si2-type with disordered TMA+ ions between the FeSe layers. Although the organic ions are not detectable by X-ray diffraction, packing requirements as well as first principle DFT calculations c…
We report on the synthesis and superconductivity of high-entropy-alloy-type (HEA-type) compounds TrZr2 (Tr = Fe, Co, Ni, Rh, Ir), in which the Tr site satisfies the criterion of HEA. Polycrystalline samples of HEA-type TrZr2 with four different compositions at the Tr site were synthesized by arc melting method. The phase purity and crystal structure were examined by Rietveld refinement of X-ray diffraction profile. It has been confirmed that the obtained samples have a CuAl2-type tetragonal structure. From analyses of elemental composition and mixing entropy at the Tr site, the HEA state for t…
Single-layer superconductors are ideal materials for fabricating superconducting nano devices. However, up to date, very few single-layer elemental superconductors have been predicted and especially no one has been successfully synthesized yet. Here, using crystal structure search techniques and ab initio calculations, we predict that a single-layer planar carbon sheet with 4- and 8-membered rings called T-graphene is a new intrinsic elemental superconductor with superconducting critical temperature (Tc) up to around 20.8 K. More importantly, we propose a synthesis route to obtain such a singl…
Very recent report [1] on observation of superconductivity in Bi4O4S3 could potentially reignite the search for superconductivity in a broad range of layered sulphides. We report here synthesis of Bi4O4S3 at 5000C by vacuum encapsulation technique and basic characterizations. Detailed structural, magnetization, and electrical transport results are reported. Bi4O4S3 is contaminated by small amounts of Bi2S3 and Bi impurities. The majority phase is tetragonal I4/mmm space group with lattice parameters a = 3.9697(2)Å, c = 41.3520(1)Å. Both AC and DC magnetization measurements confirmed that Bi4O4…
We report an easy single step synthesis route of title compound NdFeAsO0.80F0.20 superconductor having bulk superconductivity below 50 K. The title compound is synthesized via solid-state reaction route by encapsulation in an evacuated (10-3 Torr) quartz tube. Rietveld analysis of powder X-ray diffraction data shows that compound crystallized in tetragonal structure with space group P4/nmm. R(T)H measurements showed superconductivity with Tc (R=0) at 48 K and a very high upper critical field (Hc2) of up to 345 Tesla. Magnetic measurements exhibited bulk superconductivity in terms of diamagneti…
The synthesis and characterization of PVA (Poly Vinyl Acetate) doped bulk MgB2 superconductor is reported here. PVA is used as a Carbon source. PVA doping effects made two distinguishable contributions: first enhancement of Jc field performance and second an increase in Hc2 value, both because of carbon incorporation into MgB2 crystal lattice. The susceptibility measurement reveals that Tc decreased from 37 to 36 K. Lattice parameter a decreased from 3.085 A to 3.081 A due to the partial substitution of Carbon at Boron site. PVA doped sample exhibited the Jc values greater than 10^5 A/cm2 at 5…
