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Calcium ferrite (CaFe 2 O 4 )-type Li x Mn 2 O 4 was prepared via high-pressure and soft chemical synthesis method. The framework structure of CaFe 2 O 4 -type NaMn 2 O 4 was synthesized from the stoichiometric mixture of Na 2 CO 3 and MnO 2 annealed by 1273 K for 1 h under 4.5 GPa. Na/Li ion-exchange of the CaFe 2 O 4 -type NaMn 2 O 4 was carried out by soaking molten LiNO 3 at 633 K for 12 h. The electrochemical properties of the ion-exchanged CaFe 2 O 4 -type Li x Mn 2 O 4 were measured. The initial discharge profile in the voltage range from 4.0 to 1.0 V showed 458 mAh g −1 of the discharge capacity with two plateaus near 3.7 V and 2.7 V (vs. Li/Li + ). The discharge capacity was decreased with increasing the cycle number. After 30 cycles, the capacity was decreased to 375 mAh g −1 . When the range was set between 4.8 and 3.0 V, the discharge capacity was 113 mAh g −1 in initial, and 111 mAh g −1 after 50th cycle. The reference CaFe 2 O 4 -type LiMn 2 O 4 was prepared via one-step high-pressure synthesis and compared the electrochemical properties with the ion-exchanged sample. The initial discharge capacity of the one-step synthesized one was 108 mAh g −1 at 1.0 V (vs. Li/Li + ), which was 73% lower than the value of the ion-exchanged one.

(Cu, C)–Ba–O thin films have been deposited at low growth temperature of 450–570 °C by pulsed laser deposition method. A control of CO 2 gas pressure and the growth temperature, usage of BaCu y O x pellet target resulted in an expansion of twice c -axis length of BaCuO 2 structure (2c phase) and a significant rise of conductivity. Measurements of in-situ XPS suggest that the 2c phase should be (Cu, C)Ba 2 CuO x [(Cu, C)-1201]. The maximum temperature of onset of the superconducting transition and zero resistance state obtained so far were 60 and 47 K, respectively.

Transport properties of (Cu, C)Ba 2 CuO x [(Cu, C)-1201] thin films have been characterized by in situ temperature dependence of resistivity, without breaking vacuum from the deposition to the measurement. In in situ transport properties measurements, the obtained results reveal that (Cu, C)Ba 2 CuO x films exhibit T c > 20 K on the cased of conductivity at 290 K ( σ [290 K] ) > 4 × 10 2 S/cm and temperature coefficient of resistivity (TCR) > 1.5 × 10 −3 K −1 , and doping level of them should be in between under-doped and optimally-doped states. Their results suggest that there would be possible to further increases of T c , and XPS data suggest that (Cu, C)-system should have the excellent dopability in their charge reservoir and the possibility of low anisotropy.

HgBa 2 Ca n −1 Cu n O y (Hg:12( n − 1) n ) phases have the same T c independent of n and the same vortex melting line for n ⩾ 6. In these materials, there are two types of pancake pairs: those separated by the thick block of ( n − 2) inner CuO 2 planes, which are weakly coupled by the magnetic interaction, and, respectively, those separated by the thin HgBa 2 O x charge reservoir layer, which are much stronger coupled by the Josephson coupling. The vortex melting line common to all Hg:12( n − 1) n phases ( n ⩾ 6), separates two new vortex phases, pancake-molecule-glass, and pancake-molecule-liquid.

Superconducting (Cu, C)?Ba?O thin films have been epitaxially grown on (100) SrTiO3 at a low growth temperature of 500?600??C by pulsed laser deposition. The dependences of their crystallinity and transport properties on preparation conditions have been investigated in order to clarify the dominant parameters for carbon incorporation and the emergence of superconductivity. It has been revealed that the CO3 content in the films increases with increasing both the parameters of partial pressure of CO2 during film growth and those of growth rate and enhancement of superconducting properties. The present study has also revealed that the structural and superconducting properties of the (Cu, C)?Ba?O films are seriously deteriorated by the irradiation of energetic particles during deposition. Suppression of the radiation damage is another key for a high and uniform superconducting transition. By these optimizations, a superconducting onset temperature above 50?K and a zero-resistance temperature above 40?K have been realized.

The multilayered cuprates of HgBa 2 Ca n −1 Cu n O y (Hg-system) and Ba 2 Ca n −1 Cu n O 2 n (O, F) (F-system) ( n = 5–9) have been synthesized under high-pressure to investigate the variation of T c . The a - and c -parameters showed reasonable behavior: as the n increases from 5 to 9 the a -parameter approached that of an infinite layer CaCuO 2 (IL) and the average interval of c (or c /2) was close to the c -parameter of the IL. All the samples showed high T c values of about 100 and 80 K for Hg- and F-system, respectively. In addition, the T c was almost constant for n ⩾ 5 for both systems. We have shown that the T c variations can be explained using inhomogeneous charge distribution model as follows. The high T c value is maintained because the charge reservoir layer supplies enough carriers for superconductivity to the adjacent CuO 2 planes (OP) even for large n . The T c is independent of n because the carrier concentration of OP is insensitive to n for large n .

It has recently been found that the T c of TlBa 2 Ca 2 Cu 3 O y (Tl-1223) is equivalent to that of Hg-1223, known as the highest T c superconductor at present. Measurements of resistivity, Hall effect, and thermoelectric power were carried out on Tl-1223 having various doping levels from high over-doping to slight over-doping. As-synthesized materials were prepared under high pressure and deoxidized by post-annealing under various conditions. The results were compared with the data for under-doped Hg-1223 reported by Fukuoka et al. The carrier concentration estimated from the thermoelectric power in both over-doped Tl-1223 and under-doped Hg-1223 showed a simple bell-shaped T c behavior. It was also observed that the Hall effect behavior of over-doped Tl-1223 resembles that of over-doped Hg-1223. These results strongly suggest that the highest T c values for the Tl and Hg systems are nearly identical at the same carrier concentration per CuO 2 plane.

必要試料量がnlレベルであるキャピラリー電気泳動法により，高温酸化物超伝導体中のTlの価数分析法を開発した．四ホウ酸ナトリウム十水和物を泳動液に用い，アコイオン自体に紫外吸収を示すTl(I) はTl＋として印加電圧25.0 kVで泳動させ，波長215 nmでUV法により直接検出した．塩酸に溶解させているTl(III) はTlCl63－として印加電圧－30.0 kVで泳動させ，波長242 nmで直接検出した．共存イオンはイミダゾールを用い，間接紫外吸光法により定量した．実試料は，Tl系高温酸化物超伝導体0.20 mgを0.01 MのHClに溶解させて用いた．測定した2種類の試料はともに97％ がTl(III) という結果になった．本法を用いることで従来の方法よりも必要とする試料量を約20分の1に下げることができた．

Single crystals of multi-layered Ba 2 Ca 4 Cu 5 O 10( O , F )2 superconductor(F-0245) have been grown under a high pressure of 4.5 GPa . Single crystals with in-plane length of 500μm were typically obtained and flat shiny areas with more than 1 mm 2 were also observed on the surface of fractured samples. Tc values for these samples were determined by electrical resistivity measurements. These values were found to change from 70 K to 85 K by change of oxygen and fluorine contents in the starting mixture. The temperature dependence of resistivity showed characteristic of under-doped cuprate superconductors.

A layered cuprate film, (Cu,C)Ba2Can−1CunOx (n=1; (Cu,C)-1201), consisting of the charge reservoir block and the infinite layer was prepared by sputtering BaCu0.75Ox target on a (1 0 0) SrTiO3 substrate. The effects of the substrate temperature (Ts) and CO2 concentration (Cco2) in the discharge gas on the crystallinity of the films were systematically examined. The (Cu,C)-1201 film oriented along c-axis formed on the (1 0 0) SrTiO3 substrate. The φ-scan X-ray measurement of the films showed four-fold symmetry. The Cco2 and Ts strongly affected the crystallinity of the (Cu,C)-1201 film. The deposition conditions for a (Cu,C)-1201 film with a single-crystalline phase were as follows: discharge gas, Ar+CO2 (C co 2 =2–8 vol %); Ts 520–560°C and gas pressure, 1.33 Pa. Oxygen annealing of the (Cu,C)-1201 films in a sputtering chamber at near 15 Pa during the cooling process down to 100°C generated uncompensated electrical charges (holes), resulting in low resistivity. Metallic conduction down to 50 K was observed for a film deposited in Ar+CO2 gas (C co 2 =3 vol %); at a Ts of 530°C.

Single crystals of multi-layered superconductors of Ba2Can−1CunO2n(O,F)2 (F-02(n − 1)n, n = 3 and 4) have been grown under a pressure of 4.5 GPa. Crystals were obtained by cooling samples with nominal compositions of Ba2Can−1CunO2nF2 (n = 2, 2.5, 3 and 4) across the melting point. The crystals are thin plate-like shapes with typical sizes of 500 µm in plane length and 30 µm in thickness. The crystals are found to show cleavage, which will be convenient for surface sensitive measurements. The F-0223 and F-0234 crystals showed Tc of 90 K and 70 K, respectively after oxygen annealing. The temperature dependence of resistivity showed pronounced underdoped behaviour. Composition analysis showed that a ratio of Ba:Ca:Cu is close to the stoichiometric composition one. We think that the F-system is a rare multi-layered cuprate that can largely grow under high pressure and its crystals are quite valuable to study both high-Tc superconductivity and the multi-layered system.

Polycrystalline samples of Ba 2 Ca 3 Cu 4 O 8 (O 1-y F y ) 2 (0234F) with a variety of T c (55-105 K) were synthesized under high pressure. The dynamic range of the T c 50 K in an underdoped region, has been found to be remarkably wide. We also found that plate-like single crystals of 0234F (∼1 mm 2 in plane area and 30 μm in thickness) grow when samples with a nominal composition of y ∼ 1.0 are heated at high temperature (∼1150 °C). Cleavage was observed for the crystals. The 0234F will be a convenient material for investigations of physics of the multi-layered superconductors and/ or the underdoped state that has a key for understanding high-T c superconductivity.

The effects of residual carbon in precursors on phase formation of single Tl–O layer superconductors of TlBa 2 Ca n −1 Cu n O y ( n =3 and 4) have been investigated. The samples were prepared from Tl 2 O 3 and precursors of Ba 2 Ca n −1 Cu n O 2 n +1+ δ (C x ) ( n =3 and 4) with various residual carbon contents ( x =0.02–0.19). Even a small amount of carbon promotes the formation of double Tl–O layer phases of Tl 2 Ba 2 Ca n −1 Cu n O y ( n =3 and 4). Using the carbon reduced precursor ( x =0.02), a TlBa 2 Ca 2 Cu 3 O y phase is synthesized directly in a silver-sheathed tape without such elements as Pb, Bi and Sr.

TlBa 2 Ca n −1 Cu n O y ( n =3: Tl-1223 and n =4: Tl-1234) have been found to have comparable T c with Hg-system which is known to show the highest T c in superconductors. Samples were synthesized under a pressure of 3.5 GPa using precursors with small residual carbon concentrations. We found that starting composition of Tl and synthesis temperature also affect the T c . Polycrystalline samples showed T c of 133.5 (Tl-1223) and 127 K (Tl-1234) after the post-annealing in nitrogen flow, respectively. Composition analysis suggested that suppression of the substitution of Tl for Ba- and Ca-site enhances the T c .

A TlBa2Ca2Cu3Oy (Tl-1223) superconductor with an ideal composition has a much higher Tc than the established value (~120 K). The intrinsic Tc arises by suppression of Tl substitution for Ba and Ca sites, which inherently occurs in samples prepared by conventional methods. The substitution of Tl was suppressed by preserving the samples in a heavily over-doped state (Tc~100 K) which was realized by a high-pressure (solid and oxygen) synthesis method. In addition, we found several synthesis conditions for which we could obtain high-Tc samples with good reproducibility. Residual carbon in the precursor was found to be harmful for superconductivity, so that it had to be reduced as much as possible before the high-pressure synthesis. The synthesis temperature and starting concentration of Tl, which also affect Tc, had to be controlled properly to enhance Tc. Samples show that Tc≥130 K by post-annealing in a reducing atmosphere at 650-700 °C for 0.5 h to 12 h. The sample prepared with the starting composition of Tl0.75Ba2Ca2Cu3.25Oy had an almost ideal grain composition and showed a Tc of 133.5 K. This Tc is comparable with that of HgBa2Ca2Cu3Oy (Hg-1223) which is known to have the highest Tc in superconductors.

Single phase samples with the composition of (Cu, M)Ba2Ca3Cu4Oy(CuM-1234; M=C,Al,Tl,Mg,Zn) have been synthesized using high pressure technique. We have measured the pressure dependence of superconducting transition temperature (Tc) through insitu resistivity measurements up to 8 GPa for these samples, reproducibly. These samples indicated almost the same Tc-enhancement by applied pressure, in spite of their different ambient Tcvalues. The enhancement values of 8-10 K at 8 GPa pressure for these samples are found to be comparable to those of Hg-system and (B,C)-system.

We have synthesized the single phase samples of CuxC0.1Ba2Ca3Cu4Oz(x=0.2∼0.9). Transport and magnetic measurements and iodometric titration analysis were carried out for these materials. From these results we discuss the correlation between Tc, the Hall number, copper valence and oxygen content. The effect of the substituted M ions on Tcin (CuC, M)-l234 (M=Ni,Zn,Al,TI,Mg) is also discussed. We propose a unique selective carrier-doping mechanism in (Cu,C)- and (CuC,Mg)-1234 systems.

(Cu,C)–Ba–O thin films have been epitaxially grown on (100) SrTiO 3 at 500 °C by pulsed laser deposition. Their crystallinity and transport properties have been investigated in order to clarify dominate deposition parameters for carbon-incorporation and superconductivity. The present study has revealed that the growth rate positively correlates with CO 3 content and superconducting properties. In addition, the results suggest that suppression of the radiation damage from energetic particles during deposition is an important factor in obtaining a high and sharp superconducting transition temperature. The work has shown that process parameters can be optimized for growth rate, CO 3 content and minimal radiation damage allowing a superconducting onset temperature of 50 K and zero resistance temperature above 40 K to be realized.

We have succeeded to prepare Tl -1223 samples with a maximum Tc above 130K at ambient pressure using a conventional sealed quartz tube method. We found that, by adequately controlling the starting composition, it is possible to control the maximum Tc from ~120K to 130K. In order to seek the key factors for a drastic increase in the Tc, we carried out the measurements of the thermoelectric power, powder X-ray diffraction and neutron diffraction for these samples. As a result, it is found that the characteristics in the Tl -1223 samples with high Tc show essentially similar to those in the Hg -1223 with the highest Tc and are different from those in the Tl -1223 samples with low Tc. The details of the synthesis conditions, the transport properties and the refinements of the crystal structure will be presented.

The pressure dependence of the superconducting transition temperature, T c ( P ) has been measured up to 8 GPa for (B 1− x C x )(Ba 1− y Sr y ) 2 Ca 2 Cu 3 O z ( x =0.3, y =0.25; x =0.35, y =0.3) and B 0.8 C 0.2 (Ba 0.75 Sr 0.25 ) 2 Ca 3 Cu 4 O z . Large enhancement of T c under pressure was observed in the BC-1223 system. In nearly optimally doped B 0.65 C 0.35 (Ba 0.7 Sr 0.3 ) 2 Ca 2 Cu 3 O z , T c ( P ) is observed to increase from 119.6 K at ambient pressure to 133.0 K at 8 GPa. The enhancement of T c under pressure in BC-1234 was observed to be smaller than that in BC-1223. The results were discussed compared with those in the Hg-based system.

The hot press method was employed for the synthesis of a new family of the high T c superconductor (CuTl)Ba 2 Ca n −1 Cu n O 2 n +4− y . By varying the starting composition of the samples, the optimum preparation conditions for the Cu 1− x Tl x Ba 2 Ca 2 Cu 3 O 10− y ( x =0.25–0.75) phases were studied. The highest T c (121 K) sample of (Cu 0.3 Tl 0.7 )-1223 was obtained by hot press sintering at 1000°C for 3 h. Highly oriented (Cu 0.3 Tl 0.7 )-1223 samples along the c -axis were obtained by the same way.

Single crystals of CuBa 2 Ca 3 Cu 4 O y (Cu-1234) with dimensions up to 200×100×20 μ m 3 have been synthesized under high pressure using a belt type anvil apparatus. The impurity of Au, emanating from Au capsule, was found in the crystals by SEM–EDS analysis. These crystals showed superconducting transition temperature ( T c ) ranging from 105 K to 68 K and are lower than that of Au-free polycrystals ( T c =118 K). The T c values are found to decrease linearly with Au content at a substantially high rate of 7.0±0.4 K%, indicating the substitution of Au ions for Cu-sites. Superconducting anisotropy γ as estimated from the resistivity data of Cu-1234 single crystal just above T c (=102 K) has been found to be higher ( γ =5.8) than that for the Au-free polycrystals.

The surface nature of CuBa/sub 2/Ca/sub 3/Cu/sub 4/O/sub 12-/spl delta// (Cu-1234) superconducting ceramics has been characterized by photoemission spectroscopy, and an improvement of their surface electronic structure for high performance contacts has been attempted, In photoemission spectra of the specimens which had been scraped by a diamond file in vacuum, a shift of Ba core signals towards the higher binding energy side and reduction of valency of Cu were observed. This indicates that the surfaces of the conventionally treated Cu-1234 should easily lose oxygen from the vicinity of (BaO)/(CuO/sub 2-y/)/(BaO) blocks. Due to this degradation, a high contact resistivity was observed on interfaces between Au and such surfaces. The annealing in ultra-high vacuum at a low temperature below 150/spl deg/C under atomic oxygen or O/sub 3/ beams developed an intrinsic surface-electronic-structure. Due to the treatment, contact resistivity as low as 1/spl times/10/sup 18/ /spl Omega/ cm/sup 2/ was reproducibly achieved.

We report that the incorporation of hydroxide ions (OH)- significantly enhances the superconducting transition temperature (Tc) in the LnFeAsO-based superconductors (Ln1111: Ln = La, Ce and Pr). For La1111, Tc of the (OH)- incorporated sample synthesized using high-pressure technique becomes 35 K, which is higher by 7 K than the typical optimally-doped La1111 superconductors. Similar enhancement in Tc is also observed for Ce1111 and Pr1111. 1H-NMR measurement have confirmed the existence of hydrogen atoms in the samples. Accompanying the (OH)- incorporation, the lattice parameters are largely contracted, down to the values which have never been attained by any other dopings/substitutions., 8 pages, 5 figures, 1 table, Appl. Phys. Lett. to be published

The developments of high performance magnetic materials are required in various applications such as high sensitive magnetic sensing and hyperthermia in cancer treatment. Recently, Co-doped TiO2 has been received considerable attention as a candidate for such materials because of their ferromagnetic properties at room temperature. On the other hand, the phase-separated glasses and the derived glass-ceramics having unique micro-nano structure are utilized for various applications. In this study, the phase separated glass-ceramics in CoO-TiO2-SiO2 system with Al2O3 addition were prepared by melt-quenching process. The as-quenched samples consisted of the TiO2-rich phase and the SiO2-rich one which were formed by a nucleation-growth mechanism of phase separation. From the results of XRD measurements, the samples were found to have a TiO2 crystalline phase and a SiO2-rich glassy phase. The samples showed the magnetic property, which were regarded as a mixture of ferromagnetic and paramagnetic phases. The samples also showed the electric conductivity at room temperature. However, the conductivity of the sample decreased with increase of the Co content, and the temperature dependence of the conductivity of the ferromagnetic samples was different from the other ones. As a result, the Co ions in the phase-separated glass-ceramics in TiO2-SiO2 system were found to affect on both the magnetic and the electric conductive characteristics.

We report (63,65)Cu- and (19)F-NMR studies on a four-layered high-temperature superconductor Ba(2)Ca(3)Cu(4)O(8)F(2)((0234F(2.0)) with apical fluorine (F(-1)), an undoped 55 K superconductor with a nominal Cu(2+) valence on average. We reveal that this compound exhibits the antiferromagnetism (AFM) with a Neel temperature T(N)=100 K despite being a T(c)=55 K superconductor. Through a comparison with a related trilayered cuprate Ba(2)Ca(3)Cu(4)O(8)F(2)(0233F(2.0)), it is demonstrated that electrons are transferred from the inner plane (IP) to the outer plane (OP) in 0234F(2.0) and 0223F(2.0), confirming the self-doped high-temperature superconductivity (HTSC) having electron and hole doping in a single compound. Remarkably, uniform mixing of AFM and HTSC takes place in both the electron-doped OPs and the hole-doped IPs in 0234F(2.0).

We report the first superconducting tape using an iron-based superconductor (Sr,Na)Fe2As2 fabricated by the powder-in-tube (PIT) technique. Polycrystalline (Sr1−x Na x )Fe2As2 (x = 0.55), which we recently succeeded in synthesizing, was used as the starting powder. First, a silver (Ag) tube was groove-rolled into a square wire. The wire was then flat-rolled into tape form, followed by uniaxial cold pressing. The heat-treated tape exhibits a sharp superconducting transition at 34.5 K. Large transport critical current densities (J c) of over 1.0 × 104 A cm−2 are achieved at 20 K under a magnetic field of 2.5 T. J c at 4.2 K, as estimated from magnetic hysteresis curves, is 1.0 × 105 A cm−2 in 2.0 T, which is comparable to the transport J c reported for (AE,K)Fe2As2 (AE = Ba or Sr) tapes. SEM-EDX observations indicate that some Ag and As-rich material is present between (Sr,Na)Fe2As2 grains, even though no Ag was added to the starting powder. This Ag and As-rich material may strengthen grain connectivity and help to improve the transport J c.

(Sr1−xNax)Fe2As2 is a family of the so-called '122 system' of Fe-based superconductors. So far, samples with a limited composition range, i.e. polycrystalline samples for 0 ≤ x ≤ 0.42 with a maximum transition temperature (Tc) of 26 K and a single crystal with x = 0.5 and Tc = 35 K, have been synthesized. Here, we report the synthesis of single-phase polycrystalline samples of (Sr1−xNax)Fe2As2 for a wide range of x from 0 to 0.70 using a stainless-steel pipe-and-cap method. The susceptibilities in the normal and superconducting states were measured as a function of x, and an overall superconducting phase diagram was obtained. As x increased, the structural and anti-ferromagnetic phase transition temperature decreased, and superconductivity began to emerge around x = 0.35. Tc exhibited a dome-like composition dependence with a maximum onset Tc of 36.5 K for x = 0.55. The Rietveld refinement of the powder x-ray diffraction pattern at room temperature for x = 0.55 revealed structural parameters such as the lattice parameters a = 3.857(1) A and c = 12.564(1) A, an Fe–As bond length lFe–As = 2.394(1) A, an As–Fe–As bond angle αAs–Fe–As = 107.3(1)°, and an As height from the Fe layer hAs = 1.419(1) A.

We report the synthesis, superconducting properties and X-ray diffraction of a single-phase “1223” superconductor, i.e. Hg0.75Ba2Ca2.05Cu3.2O8+δ having a Tc of 102 K (as-synthesized sample) and 133 K (oxygen-annealed sample). The X-ray diffraction patterns of the 102 K phase and the 133 K phase both indicate a nearly perfect single phase, corresponding to the crystal structural arrangement of the Hg-1223 compound. The as-synthesized sample has the lattice constants a=3.848(1) A and c=15.779(0) A . A slight contraction in the c-axis is observed for oxygen-annealed samples. The resulting oxygen nonstoichiometry appears to play an important role in the enhancement of Tc from 102 to 133 K.

We have prepared V2O3 thin films on Al2O3 (0001) substrate by RF magnetron sputtering using oxygen radical and V-metal target, and studied their electronic structures by X-ray absorption spectroscopy (XAS) and X-ray photoemission spectroscopy (XPS). The as-deposited V2O3 thin films deposited at 600 °C exhibits high crystallization by oxygen radical irradiation during deposition. The electrical resistivity decreases with increasing deposition temperature, and this result is due to decreasing electron scattering. The crystal field splitting (10Dq) of the V2O3 thin film estimated from the fitting of the V 2p XAS spectrum is larger than that of the bulk crystal. In the XPS spectrum of the valence band region, the density of state (DOS) of the orbital in the V 3d state increases at around the Fermi level. These results contribute to the lattice distortion between the thin film and the substrate.

Artificially stacked structures of [(infinite layer CaCuO 2 ) k /(superconducting (Cu, C)Ba 2 CuO x :(Cu, C)-1201) l ] m were fabricated on SrCuO 2 buffer layer by means of sequential deposition of each block using pulsed laser deposition. Smooth and epitaxial growth all over the deposition cycles of (Cu, C)-1201 and CaCuO 2 were confirmed by streak patterns of in situ RHEED. In comparison with (Cu, C)-1201 single layer films, the artificial stacking resulted in a rise of superconducting properties, T c - onset and T c ( ρ =0) up to 95 K and 65 K, respectively.

Critical current densities (Jc) and irreversibility fields (Hirr) have been estimated for (B,C)(Sr,Ba)2Ca2Cu3O9 (Tc=119K) and Ba2Ca2Cu3O6(O2.yFy) (Tc=109K) from magnetization measurements. The Jc and Hirr for (B,C)(Sr,Ba)2Ca2Cu3O9 have been considerably enhanced compared with the related materials of BSr2Ca2Cu3O9 and BSr2Ca3Cu4OII. It demonstrates that properties of the sample was strongly modified by the chemical control of Ba and/or carbon substitutions. On the other hand, 0223F system showed rather low Jc and Hirr in spite of the short spacing between CUO2 layers. 0223F system should be improved the Jc and Hirr performances by a chemical (a carrier doping) control.

Single-phase samples of (Cu1-xMx)Ba2Ca3Cu4Oy (M=CO3, SO4, NO3) have been prepared by a high-pressure technique. At least about 56% and 24% of Cu site was found to be substituted successively for groups of CO3 and SO4 (or NO3), respectively. The c-axis length of (Cu1-xCx-1234 decreased linearly with increasing x. Carbon content x of (Cu1-xCx)-1234 is able to be estimated by the relation between the c-axis length and the carbon content x. Tc of (Cu1-xCx)-1234 for x 0.46. High-temperature X-ray diffraction analysis has revealed that Cu-1234 is decomposed above about 600 °C.

The single crystal of CuBa2Ca3Cu4O12-y (Cu-1234) was grown under high-pressure. The single crystal with maximum size of 250×150×30μm3 was obtained at 1150°C for 30 hours under a pressure of 4. 5GPa. The lattice parameters were a=3. 860(1)A and c=17. 942(1)A with the space group of P4/mmm. The refinement of the crystal structure with R=0. 044 showed that the Cu-vacancy between two Ba-O layers was 27%. The composition was measured by SEM-EDX(energy dispersive X-ray) system. The average values of cation ratio were Ba:Ca:Cu=2:3. 17:5. 07. The measurement of magnetization showed that Tc of the single crystal was 115K.

Samples with different fractions of structural modulation were synthesized in order to study the effect of a defective modulated structure on the critical temperature T c of Hg-1234. Electron microscopy revealed the existence of modulated and unmodulated Hg-1234 structures in these samples. Measurements of critical temperature T c on these samples revealed that the structural modulation significantly suppresses the T c . For the Hg-1234 sample without the structural modulation, the T c was found to be close to the highest T c for the Hg-1223 phase.

Nearly single phase polycrystalline samples of (Cu,Ag)Ba2Ca3Cu4Oy and CuxBa2Ca3Cu4Oy have been synthesized by a high-pressure synthesis method. The samples were characterized by X-ray diffraction analysis and electrical resistivity measurements. The magnetic field dependence of intragrain Jc for as-sintered and proton irradiated samples was estimated from measurements of magnetic hysteresis using Bean critical state model. Improvement of Jc by proton irradiation was observed at low temperature below 40 K. The intragrain Jc at 5 K and 5 T was enhanced from 105 A/cm2 to 106 A/cm2.

A high-Tc, nontoxic and low anisotropic superconductor CuBa2Ca3Cu4O12−δ (Cu-1234) has been synthesized by solid state reaction under high pressure using a pure precursor Ba2Ca3Cu4O9 and CaO2. In order to eliminate the carbonate and the hydroxide, we have used the precursor material Ba2Ca3Cu4O9 sintered above 920 °C and pure CaO2 prepared from CaO2 · 8H2O. Nearly single phase CuBa2Ca3Cu4O12−δ samples were successfully synthesized at 1000°C under 4 GPa. The sample has shown distorted tetragonal cell with the lattice constants of a=3.855(7) A and c=17.993(9) A, a superconducting transition(Tc) at 117 K and anisotropic parameter γ = ξ ab / ξc =1.6.

Annealing effect of the irreversibility fields ( H irr ) in (Cu,C)Ba 2 Ca 2 Cu 3 O y ((Cu,C)-1223) and (Cu,C)Ba 2 Ca 3 Cu 4 O y ((Cu,C)-1234) have been investigated. The samples prepared under high pressure were post-annealed in nitrogen gas in the temperature range of 400–500 °C. H irr of (Cu,C)-1234 was improved after annealing at 450 °C while T c remained almost constant. This suggests that carrier density of five-coordinated CuO 2 planes or conductivity of charge reservoir layers is changed by annealing while keeping that of four-coordinated CuO 2 planes almost constant. Both samples show H irr ≃4 T at 90 K by the post-annealing, which is quite attractive for practical application.

Polycrystalline NiSe, NiTe, CoSe, and CoTe have been synthesized by two methods, i.e., (1) the solid-state reaction in an evacuated quartz ampoule (QA) and (2) the high-pressure (HP) technique (HP) in a Au capsule using a cubic anvil cell. All the obtained samples have the nickel arsenide-type hexagonal crystal structure, except CoTe (HP), and their estimated lattice parameters, a and c, show almost the same values within 0.8% in comparison between samples prepared by the QA method and those by the HP method. On the other hand, a distinct difference between samples prepared by QA and HP processes is found in the magnetization of NiSe and NiTe. In particular, for NiTe, the temperature dependence of magnetization indicates two transition temperatures at about 20 and 130 K in samples prepared by the HP process. However, samples of NiTe x (x = 0.5, 0.66, 0.82, 1, 1.22, and 2) and NiTe containing Au prepared by QA process do not show similar magnetic orders in the temperature range between 2 and 300 K. Also, samples of NiSe (HP) show magnetic transition at ∼20 K, while those of NiSe (QA) show a magnetic inflection point at ∼10 K. To the best of our knowledge the remarkable difference in magnetic properties caused by the method of synthesis has not been reported. In this paper, we present comparative experimental results of magnetic, electric, and specific heat measurements of samples prepared by the two methods. A possible explanation for such a substantial difference in magnetic interaction will be discussed.

Here we demonstrate the technique to stabilize the ErFeAsO-based superconductor with the smallest lattice constants in LnFeAsO1-y (Ln = lanthanide) series using hydrogen doping method. Polycrystalline samples were synthesized by heating pellets with nominal compositions of ErFeAsO1-y (1-y = 0.75 ~ 0.95) sandwiched between pellets of LaFeAsO0.8H0.8 compositions at 1100 {\deg}C under a pressure of 5.0 - 5.5 GP. The sample with lattice constants of a = 3.8219 {\AA} and c = 8.2807 {\AA} shows the highest superconducting critical temperatures (Tc) of 44.5 K and 41.0 K determined by onset transitions of resistivity and susceptibility, respectively. We discuss phase diagram of Ln dependence of Tc in LnFeAsO-based superconductors., Comment: 12 Pages, 5 Figures, Accepted for publication in EPL

A change of electronic structure of (Cu,Tl)Ba2Ca2Cu3Oy with reduction annealing has been studied by X-ray photoemission spectroscopy (XPS). By in situ measurement, photoelectron Fermi level is clearly observed. The change of XPS signals indicates that the treatment above 400°C should cause electron movement from CuO2 planes to Tl–O, which should result in a re-increase of hole content and improvement of superconducting properties.

We found a drastic improvement of Tc being higher than 130 K on (Cu,Tl)-based superconductor. This improvement was achieved by annealing under the oxygen-reducing conditions. Study of the annealing effect on the resistivity and Tc is reported.

The pressure dependence of Tc for (Cu0.5Tl0.5)Ba2Ca2Cu3Oy with various T onset (T c =95.3, 128.7 and 134.6 K) has been measured. The pressure coefficients (dTc/dP) for these samples were positive, even if sample was over-doped. The values of Tc enhancement ΔTc of 12–14 K at 8 GPa for the Tc=128.7 and 134.6 K samples were comparable to those for Hg-1223 and (B,C)-1223, while ΔTc for the T c =95.3 K sample was considerably small. For the T c =134.6 K sample, Tc increased to 147.0 K at 8 GPa.

(Cu, C)-1201 films have been grown on SrCuO2 buffer layer over SrTiO3 (100) by pulse laser deposition. Effects of the insertion of SrCuO2 buffer on growth mode of the 1201 phase has been investigated by comparing in-situ RHEED pattern of the films growth on SrCuO2 / SrTiO3, SrTiO3 and NdGaO3. (Cu, Q-1201 films directly grown on SrTiO3 and NdGaO3 exhibit diffusive streak patterns in the beginning of the film growth. On the other hand, the films on the buffer show sharp streaks in the beginning from the film growth on buffer, a-axis parameters of the films on SrTiO3 and NdGaO3 estimated by RHEED patterns drastically expanded from 3.90 ± 0.06 A and 3.93 ± 0.10 A at 10 nm thick to 4.07 ± 0.05 A and 3.99 ± 0.03 A at 40 nm thick, respectively. The films on 10 nm thick buffer gradually expanded from 3.95 ± 0.05 A at 10 nm thick to 4.01 ± 0.05 A at 40 nm thick. The films on 10 nm and 20 nm thick buffer layers showed the rises of superconducting onset temperature Tc-onset to 72 K and 62 K, respectively, whereas Tc-onset of the films directly grown on SrTiO3 was about 50 K. Due to the growth mode without misfit dislocations in the beginning of the film growth, the SrCuO2 buffer could strain the 1201 phase. These results indicated that the interfacial strain should be important Tc for (Cu, Q-1201 films, and superlattice based on it.

Transport properties of (Cu, C)-1201 thin films have been characterized by in-situ four probe method without breaking vacuum, subsequent to their growth by pulsed laser deposition, in order to clarify intrinsic transport properties. Owing to the in-situ measurements, degradation of contact resistance and normal state conductivity were successfully suppressed. Obtained results reveal the positive correlation between Tc and normal state conductivity δ at 290 K, and that between Tc and temperature coefficient of resistivity (TCR) at 290 K. The films exhibit Tc(ρ=0) > 20 K on the cases of δ[290 K] > 4 x 102 S/cm and TCR > 1.5 x 10-3 K-1. The high Tc with low conductivity of (Cu, C)-1201 films indicates the presence of extrinsic defects such as grain boundaries. The absence of saturation of Tc with an increase of TCR indicates doping level of the (Cu, C)-1201 films in this study should be in between under-doped to optimally-doped states. They suggest there would be some room for further increases of Tc.

We reported that maximum TC values for Tl system superconductors TlBa2Ca2Cu3Oy (Tl-1223) can be controlled by slightly varying the starting composition. From the DC magnetization measurements, we estimated intragrain critical current densities (JC) and irreversibility fields (Birr) of Tl-1223 samples with different maximum TC values (~130 K and 120 K). These results were compared with those values for previously reported optimally-doped Hg-1223. It is found that, in the Birr -T curve at temperatures above 77K, Birr values of the Tl-1223 samples with TC~130K shows slightly higher values than that of the Tl-1223 samples with low TC and Hg-1223 samples.

The crystal structure of the high-TC superconductor TlBa2Ca2Cu3O8+δ with different maximum TC values (~132, 126 and 120 K) is investigated by neutron powder diffraction measurements. The refined values of occupancy for the excess oxygen(δ) located in interstitial positions on the Tl–O layer, O(4), are 0.775(6), 0.751(16) and 0.813(25) for the samples with a maximum TC of ~132, 126 and 120 K, respectively. It is found that the Cu(2)–O(3) bond lengths of samples with higher TC are shorter, and the value of this bond length for the Tl-1223 sample with a TC of ~132 K is almost equal to that for Hg-1223 with a maximum TC of ~135 K. It is also found that the flatness of the CuO2 planes increases with increasing TC. It appears that the structural features of the CuO5 pyramids are among the factors contributing to the higher value of TC in cuprate superconductors.

Multilayered cuprates having crystallographically inequivalent CuO2 planes are worthful materials to realize the mechanism of high-Tc superconductivity as well as a stage to ascertain new phenomena. The material synthesis of HgBa2Can-1CunOy multilayered cuprates by employing high-pressure synthesis technique is demonstrated. A starting mixture with a composition ratio of Hg:Ba:Ca:Cu:O = 1:2:n-1:n:2n+2+? was synthesized by mixing the precursor of Ba2Ca2Cu3Oy (y~7.5) with an appropriate amount of HgO, Ca2CuO3, CuO and Cu2O (or Cu). The oxygen content of the mixture was adjusted incisively by ascertaining a ratio of CuO, Cu2O (or Cu) to obtain samples. Almost single-phase samples up to n = 6 were synthesized. The X-ray diffraction analysis of the grain-aligned sample with nominal compositions of n ? 7 revealed that the sample simultaneously comprises from n = 6 up to 16 phases.

We have proposed a T c vs n relationship for multilayered high- T c superconductors from the analysis of HgBa 2 Ca n -1 Cu n O y grain-aligned samples containing n =6 to 16 phases. The sample showed a large and sharp superconducting transition at 105 K in its susceptibility vs temperature curve. This means that multilayered HgBa 2 Ca n -1 Cu n O y can maintain a high T c at least up to n ≈16, otherwise many transitions would have been observed. It is generally believed that the highest T c decreases with n for n ≥4–5 for multilayered superconductors. We conclude that the highest T c is almost constant above about n =5 if the factors reducing T c , such as disorder, are eliminated for multilayered superconductors. This behavior can be explained using an inhomogeneous charge distribution model in multilayered cuprates.

The samples of Cu 1−x Tl x Ba 2 Ca 3 Cu 4 O 12−y (x=0∼0.5) system with low Tl concentration were prepared by a high pressure techniques. The Cu 1−x Tl x Ba 2 Ca 3 Cu 4 O 12−y (Cu 1−x Tl x -1234: x=0.4∼0.5) samples show Tc of 126 K and superconducting anisotropy of γ=4. Their Tc values are higher than those of parent materials of CuBa 2 Ca 3 Cu 4 O 12−y (Cu-1234) and TlBa 2 Ca 3 Cu 4 O 11 (Tl-1234) by 8 K and 4 K, respectively. The anisotropy of Cu 1−x Tl x -1234 system is close to the value (γ=3.5) of Tl-1234 and higher than that of Cu-1234 (γ=1.6.