High-pressure Synthesis Method Research Articles

Magnetic tri-axial orientation in rare-earth-based cuprate superconductors

We report the development of a new high oxygen pressure synthesis method of orthorhombic and twin-free RE2Ba4Cu7Oy (RE247, RE = rare earth elements) superconductors and their tri-axial orientation using by a modulated rotation magnetic field. By the new synthesis method using quartz ampoule and a chemical reaction generating additional source of oxygen pressure in it, we have successfully fabricated RE247 (RE=Y, Er) polycrystals in the almost same synthesis conditions with those using a high oxygen pressure furnace. Furthermore, tri-axial orientation of these RE247 powders has been successfully accomplished using a modulated rotation magnetic field. Although our experimental studies on the magnetic orientation were performed in epoxy resin, high degrees of in-plane orientation less than 6° were achieved. Especially for RE=Y, the degree of in-plane orientation was found to be less than 1.5°, and high effectiveness of this tri-axial orientation technique was shown in principle.

Tailoring the shapes of FexPt100−x nanoparticles

FexPt100−x nanoparticles of varying composition have been synthesized with various shapes andsizes using a high pressure synthesis method which allows control of synthesisconditions, in particular the reaction temperature. Tailoring the shapes and sizes ofFexPt1−x nanoparticles allows one to control a variety of properties that are relevant to the manypotential applications of metallic nanoparticles. Shape and composition can be used to controlcatalytic activity and to achieve high packing density in self-assembled films. Variation ofboth nanoparticle size and shape has been achieved by using various different solvents. Thesolvents used in the nanoparticle synthesis can influence the product because they can playa role as surfactants. Using solvents of various types it has been possible to synthesizeFexPt100−x nanoparticles with a variety of shapes including spherical, rod-like, cubic, hexagonal andhigh aspect ratio wires. Control of nanoparticle shape opens the door to their being used invarious technological applications for which spherical nanoparticles are ineffective.

Abnormal Magnetoresistance on Non-superconducting NdFeAsO1-y

The emergence of superconductivity in Fe-based oxypnictides has attracted much attention. To determination of the cause of the inhibition of superconductivity in the nonsuperconducting oxypnictides is crucial for further increasing superconducting transition temperature. Non-superconducting oxypnictides can also be useful for the future development of the Josephson device using these materials. Thus, the transport properties of non-superconducting oxypnictides should be studied. A typical phenomenon indicative of the temperature dependence of resistivity is the appearance of a peak at around 150K. The formation of a spin density wave (SDW) is strongly suggested at around this temperature. Below this temperature, the reported temperature dependence of resistivity varies. Some of reported ones show logarithmic divergence and others show no divergence. The common tendency is a large magnetoresistance below the temperature giving the peak of resistance. It remains to be determined which tendency reflects an intrinsic property. To answer this question, we prepare two types of samples with the same nominal composition and almost the same synthesis conditions. With these samples, we measured magnetoresistance and conclude that both tendencies reflect the true electronic property of non-superconducting oxypnictides. Polycrystalline samples were prepared by the highpressure synthesis method described in ref. 3. We selected two samples designated #080515 and #080520 for the transport study. The lattice parameters of #080515 and #080520 are a 1⁄4 3:967 A and c 1⁄4 8:570 A, a 1⁄4 3:967 A and c 1⁄4 8:576 A, respectively. The oxygen content of #080515 estimated by neutron diffraction analysis was NdFeAsO0:95, which is larger than the nominal value. The difference is probably due to the possible oxidation of the starting material (Nd, Fe, or As) or oxygen gain during the synthesis. Although the oxygen content of the sample #080520 was not estimated, judging from the lattice parameters, the difference in oxygen content between the two samples is small. For resistivity measurement, we adopted the four-terminal method. Using a Quantum Design Physical Property Measurement System (PPMS), we applied a magnetic field of up to 14 T perpendicular to the electric current, which is a 7.5Hz square wave excitation of 1mA. The voltage drop parallel to the excitation current was measured, and resistance was calculated. We show the X-ray diffraction (XRD) patterns of #080515 and #080520 in Fig. 1. These two samples are almost identical in their XRD patterns. Figure 2 shows the temperature dependence of resistivity. In contrast to that shown in the XRD pattern, the absolute values and temperature dependences of the resistivities of these two samples are markedly different. The difference results from the small difference in oxygen content between the samples. The resistivity of #080515 is 60% larger than that of #080520 at 300K. Although the resistivity of #080515 has a divergent tendency at a low temperature, that of #080520 show no clear upturn at a low temperature. In both samples, we show the peak of the resistivity at around 140K. Above this temperature, the temperature dependences of the resistivities of the two samples are similar. Below 140K, magnetoresistance becomes prominent, although the position of the peak itself is insensitive to magnetic field. We plot ðRH R0Þ=ð 0H R0Þ, where 0H is the magnetic field, RH is the resistance under the magnetic field, and R0 is the resistance under a zero magnetic field, in Fig. 1. ðRH R0Þ=ð 0H R0Þ is almost qualitatively equivalent to each other within an error of 10%. The general tendency of the magnetoresistance obtained by this measurement is consistent with those in other reports. There is a peak at around 150K and below it an abnormal magnetoresistance is observed. Two typical temperature dependences below 150K are reproduced. #080515 shows a logarithmic-like upturn at a low temperature but #080520 shows no such an upturn. Our major finding is the common temperature dependence of ðRH R0Þ=ð 0H R0Þ in these two samples. Because magnetoresistance sharply starts at around 150K near the peak position, it is easy to imagine that it relates to the origin of the 150K anomaly. This anomaly is usually interpreted as an indication of the emergence of SDW triggered by structural phase transition. Anti-ferromagnetic instability was also pointed out by band calculation. In te ns ity [ ar bi tr ar y un it]

Superconductivity at 52 K in iron based F doped layered quaternary compound Pr[O1–xFx]FeAs

Here the authors report that by a high pressure synthesis method, superconductivity with an onset transition temperature at 52 K was discovered in a fluorine-doped quaternary iron-arsenide compound Pr[O1-xFx]FeAs, with the zero resistivity and Meissner transition appeared at 44 K and 50 K respectively. As the first non-cuprate compound that superconducts above 50 K, this discovery places these iron arsenide compounds to the second high temperature superconducting family explicitly.

Superconducting Properties of LaRu4As12Synthesized at High Pressure

We report on the systematic evolution of superconducting properties in filled skutterudite LaRu 4 As 12 ( T c = 10.3 K) from the resistivity and specific heat experiments. Ternary La-based filled skutterudite LaRu 4 As 12 is synthesized by the high pressure synthesis method. LaRu 4 As 12 shows a superconducting phase transition at 10.3 K. The electronic specific heat coefficient (γ) and phonon part of the specific heat coefficient (β) are γ= 57 mJ/K 2 mol and β= 0.734 mJ/K 2 mol for LaRu 4 As 12 . The upper critical field H c2 becomes ∼ 9.6 T. The upward deviation of the determined µ 0 H c2 curve from the BCS fitting suggests multiband effect in LaRu 4 As 12 .

A Resistive Transition between the Normal and Superconducting State of BaNi2P2Single Crystals

Transport properties have been investigated for the single crystals of the nickel-based phosphide with the ThCr 2 Si 2 structure, BaNi 2 P 2 which have been prepared by high pressure synthesis method. It has been proved that BaNi 2 P 2 is a rather conventional type II superconductor, which is an important clue to clear the high temperature superconductivity of the hole-doped A Fe 2 As 2 ( A =Ba, Sr, and Ca) that have the same crystal structure.

Preparation of Fe-Oxipnictides Superconductors: Solid-State Sintering, High Pressure Synthesis and Flux Method

We have fabricated the F-doped LaFeAsO superconductors via three fabrication processes; (1) solid-state sintering, (2) high pressure (HP) synthesis and (3) crystallization from flux solution. Samples prepared by these processes have unique features depending on the process such as a large volume and uniformity of the sintered pellet, variety of the compositions in the high pressured pellet and potential of growing large single crystal using fluxes. In particular, the HP synthetic process has a unique advantage that the compositional variations in the compounds were realized by a large temperature gradient within a short reaction time.

High-pressure synthesis of giant magnetostrictive PrxTb1−xFe1.9 alloys

Pr x Tb 1 − x Fe 1.9 (0⩽x⩽1) magnetostrictive alloys with cubic Laves phase have been synthesized by a high-pressure synthesis method. Crystal structure, magnetic properties, magnetocrystalline anisotropy, and the magnetostriction of PrxTb1−xFe1.9 (0⩽x⩽1) alloys are investigated. Composition anisotropy compensation is realized in Pr0.9Tb0.1Fe1.9 alloy, which shows low magnetocrystalline anisotropy and a large magnetostriction value (λ‖−λ⊥=1497ppm) at 13kOe at room temperature. These characters suggest that Pr0.9Tb0.1Fe1.9 alloy may be a promising candidate for magnetostriction application.

Structure, thermal stability and magnetostrictive properties of PrFe x (1.5 ≤ x ≤ 3.0) alloys

Polycrystalline alloys PrFe x ( x = 1.5, x = 1.8, x = 1.9, x = 2.0, x = 3.0) have been prepared by arc-melting and subsequent high-pressure synthesis method. Their structure, thermal stability, easy magnetization direction and magnetostriction are investigated. Almost single Laves phase (MgCu 2-type) is found in sample with x = 1.9. Samples with x = 2.0, x = 3.0 consist of PrFe 1.9 phase with MgCu 2-type cubic structure and α-Fe phase. The Curie temperature (238 °C) and the decomposed temperature (408 °C) of PrFe 1.9 alloys are derived from M– T curves. The easy magnetization direction of PrFe 1.9 Laves phase lies along [1 1 1] axis at room temperature which is verified by Mössbauer spectrum. Furthermore, PrFe 1.9 alloy shows a large magnetostriction λ || – λ ⊥ = 1081 × 10 −6 at a magnetic field of 13 kOe.

Bi2ZnTiO6: A Lead-Free Closed-Shell Polar Perovskite with a Calculated Ionic Polarization of 150 μC cm-2

Bi2ZnTiO6, a lead-free analogue of PbTiO3, has been prepared by high-pressure solid-state synthesis methods. Structural analysis reveals that the tetragonal distortion (c/a ratio = 1.21) of Bi2ZnTiO6 is the largest reported for any d0 B site Pb or Bi based perovskite. Significant cation displacements result in a point-charge calculated polarization of 150 μC cm-2.

Tc dependence on the number of CuO2 planes in multilayered Ba2Can-1CunO2n(O, F)2 superconductors

Multilayered cuprates of Ba2Can-1CunO2n(O, F)2 (F-02(n-1)n) with n = 5 - 9 have been synthesized by using high pressure synthesis method in order to investigate the variation of Tc. The temperature dependence of susceptibility showed that the Tc (about 80 K) does not depend on n for n = 5 - 9. This result can be explained using the carrier imbalance model in multilayered cuprates. Charge reservoir layers supply most of the carriers to adjacent CuO2 planes (OP) and the OP keeps the Tc constant even for large n.

High pressure and high temperature synthesis and characterization of a new mixed valence perovskite oxide Eu 0.62K 0.38TiO 3

A new mixed valence perovskite oxide Eu 0.62K 0.38TiO 3 was synthesized using a high pressure and high temperature method. XRD analysis showed that the sample is single phase and has a cubic structure. EPR and Mössbauer measurements indicated that the Eu ions are in mixed valence state between +3 and +2 in the sample. The high pressure and high temperature synthesis method has some advantages.

Energetics and structural stability of Cs 3C 60

Using the ab initio pseudopotential total-energy method and the density–functional theory, we study the energetics of face-centered-cubic Cs 3C 60 which is a material of great interest as a possible high transition-temperature superconductor. At the optimized lattice constant the volume per C 60 is found to be smaller than the the most-stable hexagon-coordination A15 phase, while the total energy of the fcc phase is about 0.9 eV higher than the A15 phase. These results indicate that a low-temperature and high-pressure synthesis method might be a possible way to produce the fcc Cs 3C 60 phase. In addition, it is also found that the A15 Cs 3C 60 should show a phase transformation from a hexagon-coordination phase to a pentagon-coordination phase under hydrostatic pressure.

Electrochemical synthesis of superconducting magnesium diboride films: a novel potential technique

In the present investigation, we have discovered a new technology for the formation of superconducting magnesium diboride (MgB2) films as an alternative to the conventional high-temperature and high-pressure synthesis method. This involves the combination of electrical and chemical forces developed in an electrochemical complexing bath. The growth mechanism of the MgB2 films on the silver substrate has been revealed. The MgB2 films synthesized by this new innovative method have been characterized by using energy dispersive x-ray analysis, x-ray diffraction and scanning electron microscopy techniques. They have been tested for their reproducible and durable superconducting properties. This new method of synthesis of MgB2 films is environmentally friendly, has less energy inputs and is easy to handle. Hence, it will be the cheapest and key technology for large-scale applications of MgB2 films in a variety of superconducting devices.

Single-crystal growth of silver-lead oxide Ag5Pb2O6 from fused nitrates

Abstract Single crystals of silver-lead oxide Ag 5 Pb 2 O 6 have been grown from the fusion of a 5:2 stoichiometric mixture of silver nitrate Ag(NO 3 ) and lead nitrate Pb(NO 3 ) 2 at an ambient pressure. The high oxidation ability of nitrates has enabled the formation of Ag 5 Pb 2 O 6 at an ambient pressure, although Ag 5 Pb 2 O 6 has been conventionally prepared only by means of high-pressure synthesis methods.

Study on enhancement of Tc (⩾130 K) inTlBa2Ca2Cu3Oy superconductors

A TlBa2Ca2Cu3Oy (Tl-1223) superconductor with anideal composition has a much higher Tc than the established value(~120 K). The intrinsic Tc arises by suppression of Tlsubstitution for Ba and Ca sites, which inherently occurs in samples preparedby conventional methods. The substitution of Tl was suppressed by preservingthe samples in a heavily over-doped state (Tc~100 K) which wasrealized by a high-pressure (solid and oxygen) synthesis method. In addition,we found several synthesis conditions for which we could obtain high-Tcsamples with good reproducibility. Residual carbon in the precursor was foundto be harmful for superconductivity, so that it had to be reduced as much aspossible before the high-pressure synthesis. The synthesis temperature andstarting concentration of Tl, which also affect Tc, had to be controlledproperly to enhance Tc. Samples show that Tc⩾130 K bypost-annealing in a reducing atmosphere at 650-700 °C for 0.5 h to 12 h.The sample prepared with the starting composition ofTl0.75Ba2Ca2Cu3.25Oy had an almost ideal grain compositionand showed a Tc of 133.5 K. This Tc is comparable withthat of HgBa2Ca2Cu3Oy (Hg-1223) which is known to have the highestTc in superconductors.

Preparation and Fluorescence Spectroscopy of Bulk Monoclinic Eu3+:Y2O3 and Comparison to Eu3+:Y2O3 Nanocrystals

We report the laser spectroscopic characterization of bulk monoclinic Eu3+:Y2O3, which was prepared by a high-temperature, high-pressure synthesis method. The bulk monoclinic phase has sharp spectral lines without the line broadening and “secondary phase” of Eu3+:Y2O3 nanocrystals. The unusual optical properties of site A in this material have been determined to be intrinsic to the monoclinic phase and are not a result of surface effects in the nanocrystals. The 5D0 fluorescence lifetimes are longer in the nanocrystals than in the bulk material, indicating that there is no lifetime shortening in the nanocrystals due to quenching by the proximity of surface defects.

Magnetic properties and thermal stability of PrFe 2 compound

It is thought that Pr ions make a large contribution to the magnetocrystalline anisotropy and magnetostriction of Pr-Fe intermetallic compounds. It was estimated that the magnetostriction of PrFe 2 is larger than that of TbFe 2 at 0 K. In this paper, polycrystalline PrFe 2 was prepared by a high-pressure synthesis method. Its structure, magnetic properties and thermal stability were investigated. For a multi-phase specimen, the magnetostriction constant, λ ‖−λ ⊥, is 1030 × 10 −6, comparable to that of Terfenol-D and might be larger if the single phase PrFe 2 could be obtained. The PrFe 2 compound becomes unstable and decomposes into Pr and Fe above 630 K, so it cannot be obtained by high temperature method under normal atmosphere.

Preparation of (B1−xCx)(Sr1−yBay)2 Ca2Cu3O9 with Tc=119 K

Nearly single-phase samples of (B0.6C0.4)(Sr0.25Ba0.75)2Ca2Cu3O9 with Tc=119 K have been prepared by a high-pressure synthesis method. Samples were prepared from almost stoichiometric mixture of Ba2Ca2Cu3O7, Sr2Ca2Cu3O7, B2O3 and Ag2CO3. Partial substitution of Ba for Sr is important to prepare samples from stoichiometric compositions.

High-pressure synthesis as a promising method to search for new materials

Recent progress in materials search for new high-T c superconductors by using a high-pressure synthesis method is reviewed. Particularly through a series of studies exploring the alkaline earth copper oxide system it is demonstrated how the application of high pressure can affect the phase formation and thus can provide novel materials with unusual structures or compositions.