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Here we report a new versatile technique to manufacture MgB2 massive samples, called reverse advance internal magnesium diffusion (r-AIMI). The idea focuses on the goal of obtaining dense bulk or wire samples depending on synthesis conditions. In respect to the traditional AIMI procedure, in which a central Mg rod is covered with a B corona, here a Mg tube is filled with B powder and clad in a Ti external sheath, which is quite similar to the traditional (powder in tube) technique. After cold deformation, during which several intermediate low temperature heat treatments are necessary in order to relax the Ti sheath and Mg tube, samples are reacted at high temperature and ambient pressure to form a dense MgB2 core. The MgB2 phase results are totally disconnected from metallic sheath, and can be easily extracted and characterized. Critical current density measurements show values exceeding 106 A cm−2 below 1.5 T at 20 K. In the last part of the paper, we show the effect of final heat-treatment performed under high pressure to eliminate the present void and connect the external sheath to the internal MgB2 core and so permitting the electric transfer necessary for power applications of wires.

Superconducting coils are designed for the generation of specified magnetic fields (low, intermediate, or high). To function in different field regimes, it is important to analyze the pinning mechanics and the types of pinning centers in the superconductor in a precisely defined magnetic field. Correct identification of pinning centers would allow for the formulation of approaches to increase the critical current density and critical magnetic field, ultimately making it possible to reduce the cost of producing superconducting coils (with smaller amounts of wire needed). This paper will present a method to analyze pinning centers in MgB2 superconductor wires in low, intermediate, and high magnetic fields at 4.2 K, 20 K, 25 K, and 30 K. This method allows us to elucidate the influences of doping, isostatic pressure, and reduction of the wire diameter on individual pinning centers in a specific magnetic field. In this article, we also show a method to analyze the types of pinning centers and their impact on the engineering critical current density (Jec). This method not only allows for the identification of the types of pinning centers, but also identifies which type allows for a shift in the Jec criterion of 100 A/mm2 to enable higher magnetic fields.

The effect of wire diameter reduction on the critical current density of pristine MgB2 wire was studied. Wires were treated by a hot isostatic pressing method at 570 °C and at pressures of up to 1.1 GPa. It was found that the wire diameter reduction induces an increase of up to 70% in the mass density of the superconducting cores. This feature leads to increases in critical current, critical current density, and pinning force density. The magnitude and field dependence of the critical current density are related to both grain connectivity and structural defects, which act as effective pinning centers. High field transport properties were obtained without doping of the MgB2 phase. A critical current density jc of 3500 A mm−2 was reached at 4 K, 6 T for the best sample, which was a five-fold increase compared to MgB2 samples synthesized at ambient pressure.

Hot axial and hot isostatic pressing was applied for single-core MgB 2 /Ti tapes. Differences in transport current density, n -exponents and critical current anisotropy are discussed and related to the grain connectivity influenced by pressing. The magnetic Hall probe scanning measurements allowed observing the isolated regions for axially hot pressed sample attributed to the longitudinally oriented cracks introduced by pressing. The highest current densities were measured for the tape subjected to hot isostatic pressing due to improved connectivity.

Novel magneto-resistive memory effect is demonstrated, which appears in lithographically patterned Y-shaped, three-terminal nanostructures, consisting of three nanowires joined in one point, formed in the epitaxial layer of a ferromagnetic (Ga,Mn)As semiconductor. The effect, in which the zero-field resistance of a pair of nanowires depends on the direction of the previously applied magnetic field, results from a rearrangement of magnetic domain walls, contributing an extra resistance, between different pairs of nanowires in the structure. Two-state behaviour of the nanostructure resistance provides its usefulness for applications in non-volatile memory devices.

Low-temperature charge-carrier transport in simple magnetoresistive nanodevices, consisted of narrow constrictions of submicron width in the epitaxial layer of a ferromagnetic (Ga,Mn)As semiconductor, has been investigated and correlated with magnetic properties of the layer. The devices containing constrictions; revealed abrupt jumps of a reduced resistance that appeared when the sweeping magnetic field crossed the regions of the coercive field of the layer magnetization. In contrast, the non-constricted reference device displayed abrupt jumps of an enhanced resistance at the same values of magnetic field. We interpret the both features, whose positions on the magnetic-field scale reflect the hysteresis loop of magnetization, as manifestation of domain wall contribution to the (Ga,Mn)As layer resistance. The negative contribution of a domain wall to the resistance in the constricted device results most likely from the suppression of the weak localization effects by a domain wall located at the constriction. (Less)

In situ nano-SiC doped MgB2 wires were fabricated from MgH2 and B powders. Hydrostatic extrusion, followed by rotary swaging and two-axial rolling, were applied as the forming processes. The critical current Jc of MgB2 wires, made from MgH2 and B powders, was significantly improved by nano-SiC doping. Nano-SiC doping substantially increased the upper critical (irreversibility) field Bc 2 above 20 T. The maximum Jc values were measured for samples having 6 at.% SiC in low field and for those having 12 at.% SiC in high field, above 10 T. During the final sintering at 670 °C, the SiC decomposed and formed an Si-rich layer at the inner circumference of the Fe sheath. The composition of the core of SiC doped wires is more inhomogeneous in comparison to undoped ones, with MgO, Mg2Si and probably Mg2SiO4 as the major segregated phases. Strong segregation of Si within the MgB2 core was also observed. The highest Tc−mid = 39.3 K was measured for undoped wire. For the optimal SiC doping amount ~6 at.%, at high field, there was no difference in Jc between hydrostatically extruded and hydrostatically extruded plus two-axially rolled wire. This can be attributed to the beneficial effect of hydrostatic extrusion, which causes higher density of the core in comparison to traditional deformation processes.

From the beginning of the Mg–B system investigations, pressure was an important factor in procedures obtaining the bulk superconductors for application purposes: at hot isostatic pressing (HIP-ing), annealing under inert or active gas medium, i.e. argon with hydrogen and nitrogen, or for extrusion methods for wires manufacturing. MgB 2 reveals interesting properties. We present the current state of our technological efforts in improving the microstructure and superconducting properties of this material, with use of the high gas pressure and high temperature treatment of samples crystallized in crucibles made of BN and SiC. As the precursor we mainly use the commercial MgB 2 powder. The results of microstructure investigations and XRD analyses are presented.

A superconducting Hg0.7Re0.3Ba2Ca2Cu3O8+δ thick film on a polycrystalline LaAlO3 (LAO) substrate was obtained by a two-step method by screen-printing a Re0.3Ba2Ca2Cu3Ox precursor coating on the substrate followed by high-pressure gas firing in Hg vapour. Morphological observations have revealed that the adherent to the ceramic substrate film exhibited highly porous microstructure composed of plate-like crystallites characterized by a superconducting transition temperature of about 110 K. The major phases identified were a high-Tc (Hg,Re)-1223 phase and a low-Tc (Hg,Re)-1212 phase. Non-superconducting secondary impurity phases were also identified. Energy dispersion X-ray spectroscopy analyses at the substrate/film boundary showed a thin continuous layer of BaLa2O4 compound, the presence of which confirmed chemical interaction between the LAO substrate and (Hg,Re)–Ba–Ca–Cu–O film.

Single-core MgB2/Cu and MgB2/Fe/Cu wires and tapes have been made by the powder-in-tube method with the use of commercial MgB2 powder (Alfa Aesar) involving hydrostatic extrusion and two-axial rolling processes. High-pressure post-treatments such as cold isostatic pressing, double hydrostatic extrusion and uniaxial pressing were applied. The grain connectivity, Ic(B) curves, pinning in MgB2 grains, upper critical field, deformation homogeneity, compact density and preferable alignment crystallites for the [001] (c-axis) direction were all improved and enhanced by application of various high-pressure treatments for the MgB2 compound and composites. Hydrostatically extruded MgB2 wires have been shown to be better than rolled wires and are very promising for possible application in windings.

Single-core MgB2 wires and tapes have been made by the powder-in-tube (PIT) method using commercial MgB2 powder (Alfa Aesar). Composites have been made using the two-axial rolling process in Cu and/or Fe/Cu sheaths. Alternative deformations by wire drawing, rotary swaging and cold isostatic pressing have been applied to PIT wires and tapes. Current–voltage characteristics and transport current densities in the self-field and in the external field were measured. It was found that the grain connectivity of ex situ MgB2 is affected by the applied sheath and the mode of deformation. Two-axial rolling has generated the highest powder density resulting in the best grain connectivity. The highest transport current densities of 8700 A cm−2 and 55 830 A cm−2 were measured for Cu and Fe/Cu sheathed square wires, respectively. Cold isostatic pressing at 1.5 GPa has increased current density and n-exponent, which suggests an improvement in grain connectivity. It was found that the external pressure improves the inter-grain connectivity but decreases the pinning in MgB2 cores.

In this article, we report the results of a study that shows the existence of pinning centers inside grains and between grains in NbTi wires. We accurately show the ranges of magnetic fields in which the individual pinning centers operate. The pinning centers inside grains are activated in high magnetic fields above 6 T. We show the range of magnetic fields in which individual defects, dislocations, precipitates inside grains and substitutions in the crystal lattice can operate. We show the existence of a new kind of high field pinning center, which operates in high magnetic fields from 8 to ∼9.5 T. We indicate that dislocations create pinning centers in the range of magnetic fields from 6 to 8 T. In addition, our measurements suggest that the peak effect (increased critical current density (J ) near the upper critical field (B )) could be attributed to martensitic (needle-shaped) α′-Ti inclusions inside grains. These centers are very important because they work very effectively in magnetic fields above 9.5-10 T. We also show that the α-Ti precipitates (between grains) with a thickness similar to the coherence length create pinning centers which work very effectively in magnetic fields from 3 to 6 T. In magnetic fields below 3 T, they act very efficiently in grain boundaries. The measurements indicate that the pinning centers created by dislocations only can be tested by transport measurements. This indicates that dislocations do not increase the magnetic critical current density (J ). Cold drawing improves pinning centers at grain boundaries and increases the dislocation density, and cold-drawing pinning centers are responsible for the peak effect.

MgB2 single-filament tapes and wires with Monel/Nb sheath were produced by the Powder in Tube (PIT)-technique using MA in-ex situ powder. This powder prepared by mechanical alloying (MA) of Mg and B was finally reacted to MgB2 at 700°C. The amount of MgB2 after annealing was about 91 wt%. Additionally 9 wt% MgO secondary phase was found. The primary crystallite size was about 25 nm. Critical current density measurements have shown relatively high values of Jc = 104 A/cm2 at 6.7 T for unsintered tapes in parallel magnetic field. Heat treatment at temperatures of up to 900°C could not improve these values, probably due to MgO hindering the sintering process.

Superconducting phases of 2212-type, with the general formula Tl2−xHgxSr2Ca1Cu2Oz, were synthesized from metal oxides in closed silica tubes at 880°C. The most phase-pure sample was obtained for x=0.7. A mixture with the nominal composition Tl1.3Hg0.7Sr2Ca1Cu2Oz, used in a single-crystal growth in a high-temperature high-pressure gas trap furnace (HTHP), gave plate-like crystals with a maximum diameter of 500 μm, having unit cell parameters which could be refined to a=3.796 A and c=28.433 A (space group I4/mmm). The structural details were investigated by X-ray single-crystal analysis (Rw=0.025). Both alkaline-earth metal sites in the structure are probably mixed, but with different Ca/Sr ratios. As previously reported, some copper entered the (Tl,Hg) site in the high-pressure synthesis, giving a resulting composition of (Tl0.8Hg0.7Cu0.5)(Sr1.7Ca0.3)(Ca0.7Sr0.3)Cu2O7.5 according to energy dispersive spectrometry (EDS) analysis and structural refinement. Tc (onset) for both powder and single-crystal samples, as prepared, was about 45 K, as determined by AC susceptibility.

The properties of single crystals and thin/thick layers of high-T c superconductors (HTS, up to 135 K) made under equilibrium (p, T) conditions of vapour and oxygen are presented. The special high gas pressure apparatus combined with a method of avoiding impurities from the outer volume of the crucible was designed and successfully applied in high pressure experiments. This apparatus was used successfully in experiments with active gases such as oxygen and nitrogen, as well as chlorides, heavy metals, sulphur, fluoride, potassium, sodium and oxides, whch all produce very high partial pressure. As a result we obtained large single crystals of the mercury family of HTS compounds. The obtained single crystals and thin layers reveal a high chemical stability, which suggests their possible future application as superconducting microelectronic devices. The method presented has been successfully applied to obtain other compounds, e.g. (the HgTI-HTS family), YBCO, infinite layer and FeS 2 applied for modern thin layer photovoltaic cells.

Here we report a few methods of avoiding formation of the CaHgO 2 phase during annealing and crystallization of mercury based superconducting ceramics. These methods are based on the following principles : rapid temperature raise to pass the temperature range at which CaHgO 2 easily forms, combined temperature and pressure quenching, diluting gas carrier concentration and processing highly reactive fine-grain-size powder made by the sol-gel method. The report is supported with observations made by the XRD, SEM and high-pressure DTA methods. Some of the observed reactions between the crystallized HTS materials and the various crucible materials are reviewed. This is important because processing the mercury based HTS materials encounters problems caused by high reactivity of mercury vapours. It results in limited corrosion resistance of crucibles and substrate plates. The choice of BaZrO 3 is suggested as the corrosion resistant crucible material.

We report investigations on chemical reactions among flux containing Hg, Ba, Ca, Cu, O and crucibles made of Al/sub 2/O/sub 3/, Y/sub 2/O/sub 3/ and BaZrO/sub 3/. Our research work on oxide superconductors containing mercury allowed us to compose the first approach of p-T-x conditions of synthesis. We obtain quite large (up to 2/spl times/2 mm/sup 2/), flat single crystals. We present the results of our investigation of the influence of p-T-x conditions on reactions between the batch and the various crucibles. XRD patterns and morphology study by SEM and EDX analysis are shown. We conclude that the BaZrO/sub 3/ crucible is the most neutral for the crystallization process.

We report the first measurements of the in-plane transport properties of single crystals of the four-layer superconductor HgBa 2 Ca 3 Cu 4 O 10+σ with a transition temperature of 130 K. In the normal state the temperature dependence of the electrical resistivity and the Hall coefficient indicates that these crystals are underdoped. For the cotangent of the Hall angle we found a T 2 dependence. In the mixed state, the following form holds for a universal correlation between hall resistivity ϱ H and electrical resistivity ϱ : ϱ H ≈ ϱ n , with n = 1.75.

We report the first measurements of the in-plane transport properties of single crystals of the four-layer superconductor HgBa2Ca3Cu4O10+δ with a transition temperature of 130 K. In the normal state the temperature dependence of the electrical resistivity and the Hall coefficient indicates that these crystals are underdoped. For the cotangents of the Hall angle we found a T2 dependence.

Crystals of Hg0.5Pb0.5Ba2Ca4Cu5O12+δ were measured on an X-ray four-circle single-crystal diffractometer and the crystal structure was refined to R = 0.033. The onset of the superconducting transition of the crystals ranges from 101 K-115 K. The space group is P4/mmm and lattice parameters of the five-layer material are a = 3.8529(3) A, and c = 22.172(2) A . Hg is partially substituted for Pb and heavy atoms are shifted away from the origin by ∼0.38 A . Stacking faults of 1234 or 1256 material are manifest in the Fourier maps, and the amount was refined to 4.4%. These stacking faults induce an additional electron density at the ideal O(4) site and mask a possible oxygen occupancy at ( 1 2 , 1 2 , 0 ). However, electron density is observed at a distance of 0.6 A from ( 1 2 , 1 2 , 0 ), suggesting a shift of the excess oxygen atom from its ideal position. Bondlengths and distances show systematic changes with increasing number n of CuO2 layers. Changes occur mainly in the rock-salt type layer, whereas the CaCuO2 units remain stable over the whole H-12(n−1)n series.

We evaluate the effects of high pressure during annealing on the structural and superconducting properties of Ag-doped FeSe bulks. The results obtained in this work indicate that the annealing at high pressure increases the critical temperature, upper critical field and irreversibility field due to the improved uniformity and grain connectivity.

In this study we show that dominant point pinning mechanisms in SiC doped MgB2 wires can be obtained by annealing in high isostatic pressure. The results indicate that the point pinning centers increase the critical current density in medium and high magnetic fields, but not at low magnetic fields. In addition, our study shows that dominant pinning mechanism changes from point to surface type with increase of magnetic fields. An MgB2 wire heat treated in a high pressure of 1.4 GPa shows a high critical current density of 100 A mm−2 in 13 T at 4.2 K. Scanning electron microscope studies show that high isostatic pressure increases the density of the MgB2 material, eliminates voids, allows for small Si precipitates and homogeneous distribution of Si precipitates. Transport measurements E - B and E - I show that the MgB2 wires manufactured by Hyper Tech Research did not heat up after transition into a normal state. This is important for applications in coils.

Crystals of Hg0.8Pb0.2Ba2Ca3Cu4O10.14 were measured on an X-ray four-circle single-crystal diffractometer and the crystal structure was refined to R = 0.023. The space group is P4/mmm and the lattice parameters are a = 3.8530(5) A , and c = 18.968(3) A . Lead is incorporated at the Hg site, but it is shifted slightly from the origin in the z = 0 plane. A model of Pb4+ clusters in the basal plane is proposed, which is in agreement with recent TEM results. A reduction of electron density at the Hg site is attributed to the substitution by Cu or CO3 groups. Stacking faults of 1223 or 1245 material are manifested in the Fourier maps, and it was possible to refine the amount to 3.8%. However, these stacking faults induce additional electron density at the O(4) site ( 1 2 , 1 2 0 ), and cause an overestimation of the excess oxygen content, if it is not corrected carefully. The bondlengths are distances are in agreement with those of other members of the Hg-12(n−1)n series, and show systematic changes with increasing number n of CuO2 layers. The effect of stacking faults on the diffraction of all members of the Hg-12(n−1)n family is discussed, and a method for their determination is given.

Single crystals of the Hg 1− x Pb x Ba 2 Ca n −1 Cu n O 2 n +2+ δ (x = 0 and 0.2) and infinite-layer CaCuO 2 compounds have been grown using a high gas pressure. The Hg 0.8 Pb 0.2 -1234 single crystals of a size up to 0.5×0.5×0.05 mm 3 have a T c onset of 129 K. Sing le crystals of the CaCuO 2 of a size up to 2×1×0.05 mm 3 have been obtained without stabilizing additives of Sr or Li. The T c onset varies between 70 and 100 K. X-ray structural refinements have been performed on the CaCuO 2 and Hg-1234 single crystals. HRTEM investigations proved a high quality of the crystal structure of the Hg-12 ( n -1) n crystals.

A comparison of fast-neutron irradiation effects on the irreversibility line (IL) and the intragrain critical current densities ( J c ) in the 90 K and the 60 K phase of YBa 2 Cu 3 O 7- x (123) and in YBa 2 Cu 4 O 8 (124) ceramics is presented. The 124 compound shows a transition into the reversible regime at distinctly lower temperatures and fields than the 90 K phase of 123. However, the IL of 124 lies above the one of the 60 K phase. Upon irradiation we observe a pronounced shift of the position of the IL to higher fields and temperatures for the 60 K phase of 123 and for the 124 compound. The IL remains almost unchanged in the 90 K phase of 123 at the relatively low fluences employed so far. We also observe an increase of J c after irradiation. The values of the J c enhancement as well as their temperature and field dependence vary considerably among these compounds.

In this paper we present the results of critical current (I c) measurements of MgB2 wires made with two different set-ups of the four-point probe method: current sweep type—constant magnetic field and increasing current, and field sweep type—constant current and rapidly increasing magnetic field. Results from magnet field sweep type measurements can be interpreted by a new physical concept—a jump of the electric field in low magnetic fields. This physical concept can be correlated with damages in the Nb-barrier existing in the MgB2 wire and be employed as a detection scheme. The damage in Nb barrier reduces critical current density (J c) and complicates the study on critical temperature (T c), upper critical field (B c2), irreversible magnetic field (B irr), pinning force (F p), and pinning centers in superconducting MgB2 wires. Our proposed method to detect damages in Nb barrier would benefit efforts in development and applications of MgB2 wires.

Multifilamentary MgB2 wires were annealed under the high pressure of low-friction, solid state media such as BN and graphite powders. The idea was to replace the hot isostatic pressing in argon medium, which is beneficial to wires transport properties but is difficult for application on an industrial scale. The experimental results show that annealing in BN or graphite under 200 MPa leads to enhancement of the critical current, similar to that observed earlier for high pressure argon annealing. An unwanted effect of the process is the flattening of the round wires, which after the treatment yields an elliptical cross section with b to a ratio of around 85 ± 5%. Comparison of critical currents and microstructure of samples synthesized with different parameters are presented.

Unreacted MgB2 wires were made at Hyper Tech Research, USA by a continuous tube forming and filling method using mixtures of Mg and B with and without SiC powder additions. All of the wires underwent hot isostatic pressure (HIP) treatment at the Institute of High Pressure. The first part of the wire was annealed at a pressure of 1 GPa, and the second part was annealed at 0.1 MPa. In this work, we show the influence of high pressure on critical current density (Jc), pinning force (Fp), critical temperature (Tc), irreversible magnetic fields (Birr) and the Fp scaling and microstructure of MgB2 wires. The results obtained indicate that after annealing at high pressure, the MgB2 wires show increases of Jc and Fp in high magnetic fields (8 T–12 T); in SiC doped MgB2 wires, Fpmax shifts to higher magnetic fields. We also compared the Jc of the doped and undoped MgB2 wires (without HIP and with HIP). The scanning electron microscope (SEM) results show that HIP increases the density of MgB2 material and improves its uniformity.

Unreacted MgB2 wires fabricated from SiC-doped precursor material by Hyper Tech Research, Inc. have been used to make small-diameter (14 mm) superconducting coils. All coils made of 500 mm length wires were subjected to hot isostatic pressure (HIP) treatment. The critical current density (Jc) parameters of coils were compared to straight samples characteristics. Both types of samples have been measured in perpendicular magnetic field configuration for Jc and pinning force density (Fp) evaluation. No significant Jc difference between the long wires on coils and straight wires was found. These results suggest that the critical current (Ic) for coils can be determined for straight samples (25 mm). SEM analysis indicated that a small diameter of the coil does not influence the structure of in situ MgB2 wire. (Some figures may appear in colour only in the online journal)

Cost-effective MgB2 wires are highly sought after to replace the widely used NbTi conductors in superconducting magnets, e.g.?for magnetic resonance imaging (MRI). One method of choice for lowering conductor costs is to use a less expensive barrier and sheath material. From this point of view copper is a good candidate for the sheath, and additionally has other advantageous properties, e.g.?the best electrical and thermal conductivity at operating temperature. One major disadvantage of copper is its high chemical reactivity. This material reacts fast with magnesium and forms Mg?Cu alloys, removing the starting element necessary for MgB2 formation. To prevent this reaction, a special coaxial architecture was applied using ex?situ? MgB2 powder as a chemical barrier between the copper sheath and the in?situ? MgB2 powder core. The Glidcop? (dispersed strengthened copper) sheathed MgB2 wires with an ex?situ barrier have been fabricated by the conventional powder in tube (PIT) method. Besides avoiding the reaction of Mg and Cu, the barrier also contributes to the superconducting core fraction and increases the filling factor up to 50%. The Glidcop? sheathed wires with an ex situ?MgB2 commercial powder used as a barrier have been successfully drawn to a diameter of 1.2?mm and then a pressure-assisted heat treatment was applied. For our case of specified in?situ and ex?situ powders the pressure-assisted preparation of at least 0.15?GPa was found to be important for the densification of the ex?situ barrier.

Tl and Hg based HTS layers are the key materials for electronic devices applications. We have reported fabrication method of thin films on SrTiO 3 and LaAlO 3 substrates with T c up to 134 K and J c over 10 6 A/cm 2 at 77 K, [1]. An important progress in optimization and reproducibility of the growth process was achieved by the knowledge of the phase equilibrium acting during high gas pressure annealing, realized by precise DTA. The thermodynamic data related to oxygen content in the system allowed us to choose the optimum process conditions. We have observed large differences in between Hg and Tl family crystallization process, related to the liquid phase composition and especially to their oxygenation state. For the Hg compounds the crystallization takes place on the surface between the liquid and vapor, while for Tl the whole growth is completed in the liquid phase. Therefore, the Tl compounds are much likely to be grown by the liquid phase epitaxy method. In the case of the Hg family superconductors growth, the effect of Mo substitutions was investigated in order to eliminate the surface growth problem, and to reduce the high Hg partial pressure in the crucible.

Synthesis and properties of high-T c superconducting (Hg 1−x Re x )Ba 2 Ca 2 Cu 3 O 8+δ (x=0.05÷0.2) single crystals and films obtained by high pressure gas method are presented. The influence of Re-doping on their microstructure and superconductivity is discussed. The powder of Ba 2 Ca 2 Ca 3 O y and ReO 2 was used to prepare the precursor material, which was mixed with HgO to prepare pellets for high pressure synthesis of single crystals. After homogenization at 860°C for 1 h crystallization from the melt occurred at temperatures between 1060 and 950°C with the cooling rate of 3–5 °C/h and 50 °C/min below 950°C. The Hg 1−x Re x Ba 2 Ca 2 Cu 3 O 8+δ films were prepared by depositing the precursor film by laser ablation and by liquid phase epitaxy (LPE) on the single-crystalline substrates of SrTiO 3 and LaAlO 3 . Precursor films were made by the deposition of 1–3 μm thick amorphous layers of Ba 2 Ca 2 Cu 3 O y + ReO 2 .

The in situ technique for producing MgB2 conductors consists of filling a mixture of Mg powder and B powder into a tube, deformation to the shape of the conductor, and reaction at the end of the process. To make tapes by the in situ method, a low cost and ductile sheath material is needed. Unfortunately precursor powder partially reacts with a lot of materials, such as Cu, Fe and Ni, which can be used as a sheath. In order to produce cheap, high-performance MgB2 conductors a barrier able to prevent this reaction is needed. In this study ex situ MgB2 is used as this barrier. This paper compares the effectiveness of the barrier in preventing reaction in Fe and Cu tapes heat treated under ambient pressure and under high gas pressure conditions. It was found that this barrier is effective at preventing reaction between Fe and B, and sufficient to prevent Cu–Mg reaction in the case of high pressure sintering. This novel technique allows one to obtain good Je values in a parallel field because of the possibility of achieving a high superconductor filling factor (in excess of 60%), which is usually very challenging in powder in tube (PIT) composite conductors with a diffusion barrier.

Single crystals of the HgBa 2 Ca n−1 Cu n O 2n+2+δ compounds have been grown using a high gas pressure. The Hg1234 single crystals have a T c of 129 K. X-ray and TEM investigations proved the high quality of the crystal structure. Single crystals of the CaCuO 2 infinite layer compound of a size up to several mm 2 have been obtained under a high gas pressure without stabilizing additives of Sr or Li. The T c of the as grown crystals is 70–80 K

The HgBa 2 Ca n−1 Cu n O 2n+2+δ ceramics have been synthesized for n=2 and 3 using a gas pressure technique. The kinetics of the formation reaction of Hg1223 has been investigated at high gas pressure. The X-ray and magnetization measurements confirmed the synthesis of Hg1223 and Hg1212 compounds with T c of 134 and 128K respectively.

Single crystals of HgBa 2 CaCu 2 O 6+δ (Hg-1212) and HgBa 2 Ca 2 Cu 3 O 8+δ (Hg-1223) were grown from the melt at an argon pressure of 10 kbar. Electron microscopy, as well as single crystal X-ray diffraction studies show that the crystals are well ordered. The EDS analysis indicates the presence of a minor amount of other cations replacing Hg, Ba and Ca in the structure. Refined fractional coordinates and thermal parameters are given for a crystal of Hg-1223 type. Magnetic and resistive measurements show a T c of 133 K for the Hg-1223 phase.