*1PO3-90 Superconductivity at 76 K in Hg-1222 cuprate: (Hg,M)Sr₂(Ln,Ce)₂Cu₂Oz (M = Ti, V, Cr, Mo, W, Re; Ln = Sm-Er)

E. Kandyel, A. Yamomoto and S. Tajima, SRL/ISTEC, 10-13 Shinonome, 1-Chome, Koto-ku, Tokyo 135-0062 Japan

Presenting Author: E. Kandyel

Since the discovery of superconductivity in (Ln,Ce)₂(Ba,Ln)₂Cu₃O₁₀, several layered cuprates with 1222-type structure have been reported, such as: MSr₂(Ln,Ce)₂Cu₂O_z (M = (Tl,Pb), (Pb,Cu), Nb, Ta, Al, Ga). Some of them show superconductivity with T_c’s between 10-43 K after annealing under high oxygen pressure.

It is well known that, Hg-based superconducting family show the highest T_c’s among all known HT_c-superconducting families. Thus, it is interesting to prepare Hg-1222 compounds which may show higher T_c compared with known 1222 compounds. We systematically synthesized (Hg,M)-1222 cuprates, (Hg,M)Sr₂(Ln,Ce)₂Cu₂O_z under 2 GPa at 1100° C. Single or nearly single-phase samples are successfully obtained for M = Ti, V, Cr, Mo, W and Re, and for Ln = Sm-Er. All synthesized samples, except for the compound with Cr, show bulk superconductivity with large Meissner volume fractions. T_c is found to increase with increasing valence of the cation M and with decreasing ionic radius of Ln. The maximum T_c of 76 K is obtained for (Hg_0.75W_0.25)Sr₂(Gd_0.75Ce_0.25)₂Cu₂O_z. To the best of our knowledge, this T_c is the highest one ever reported for 1222-type superconductor.

*This work was supported by the New Energy and Industrial Technology Development Organization.

1PO3-91 Reaction mechanism in the high pressure synthesis of Hg-cuprates : an in situ synchrotron diffraction study

Pierre Bordet 1, Sylvie LeFloch 1, Catherine Bougerol-Chaillout 1, Alain Prat 1, Benoît Antérion 1, and Mohammed Mézouar 2. 1 Laboratoire de Cristallographie CNRS, BP166, 38042 Grenoble Cedex 9, France. 2 ESRF, BP220, 38043 Grenoble Cedex, France.

Presenting Author: P. Bordet

The high pressure-high temperature (HP-HT) synthesis technique is of growing importance for the discovery of new HTSC materials. However, it is still based on a trial-and-error strategy, and little is known about chemical reactions in HP-HT conditions.

In order to improve the HP-HT process, the reaction mechanism has to be understood. Therefore, we have undertaken for the first time an in situ study of the HP-HT synthesis by using synchrotron x-ray diffraction.

Three experiments were carried out at the ESRF ID30 beam line, using high energy photons (78 keV) and two-dimensional detectors. HP-HT conditions were obtained by using a Paris-Edimbourgh type cell. The reactions were followed by taking diffraction images every 30 s. The laboratory conditions (pressure of 3-4 GPa, temperature up to 1100°C, gold capsule, graphite furnace) were carefully reproduced.

The experiments focused on the synthesis of Hg-1201 and Hg-1223. In both cases, single phase materials were obtained. New intermediate phases were observed during the synthesis, and identified later on quenched samples. For Hg-1223, a peritectic decomposition into Hg-1234 and liquid (Hg-1212) was observed at higher temperatures, which could provide a way for single crystal growth. The results obtained using this fascinating new technique will be detailed at the conference.

1PO3-92 TEM Study on a New Ca-Cu-O Phase in HgBa₂Ca₂Cu₃O_8+s Synthesized Under High Pressure

J.H. Du, Dong Su, H.M. Shao, and J.S. Zhu, National Laboratory of Solid State Microstructures, Department of Physics, Nanjing University, Nanjing 210093, P.R. China

Presenting Author: D. Su

A Transmitted Electronic Microscopy (TEM) study was performed in the samples of HgBa₂Ca₂Cu₃O_8+s synthesized at high pressure and high temperature. A new Ca-Cu-O phase with a monoclinic structure (This result is similar to that got by X.-J.Wu et. [1]) has been found. It belongs to a space group P₂₁/c, with lattice parameter: a=5.38Å,b=5.85Å,c=16.25Å, and b =104.6. Based on the TEM observation, the structure of new phase has been studied and the twin structure of it has been determined with (1 0 0) twin plane. And the mechanism for formation of the new phase is discussed in this paper.

[1] Physica C 228 (1994) 292-298.

*1PO3-94 High-pressure synthesis and superconducting properties of (Cu,Cr)-12(n-1)n and (Cu,V)-12(n-1)n series of phases

Eiji Takayama-Muromachi, Andrei T. Matveev, Shan Yu, and Nikolai D. Zhigadlo, National Institute for Research in Inorganic Materials, 1-1 Namiki, Tsukuba, 305-0044 Japan

Presenting Author: E. Takayama-Muromachi

We prepared homologous series of Cr- and V-based cuprate superconductors under high pressure condition. The (Cu,Cr)Sr₂Ca_n-1Cu_nO_2n+3 phases exist at 6 GPa for a wide range of n, n=1-9, while the (Cu,V) Sr₂Ca_n-1Cu_nO_2n+3 phases for n=3-7. They have M-12(n-1)n-type structures with M=(Cu,Cr) [or (Cu,V)] with a stacking of planes, SrO-(Cu,Cr)O-SrO-CuO2-(Ca-CuO₂)n-1. The highest T_c for the former series is 103K at n=3 and that for the latter is 107K at n=4. In the charge reservoir layers, Cu and Cr (or V) atoms are placed randomly giving simple tetragonal lattices. These phases show very high J_c values under magnetic field which may be related to the partial occupation of the Cu atom and the random arrangement of Cu and Cr (or V) in the charge reservoir layer.

It was found that the Sr atoms of the above series of phases can be substituted partially by Nd and such a substitution affects T_c and J_c. The substitution effects on the superconducting properties will be discussed in details.

1PO3-95 Stability of Cu_1-xBa₂Ca_n-1Cu_nO_y under several atmosphere

Yasuharu Kodama 1, Akira Iyo 2, and Hideo Ihara 2. 1 National Industrial Research Institute of Nagoya, 1-1 Hirate-cho, Kita-ku, Nagoya 462-8510 Japan. 2 Electrotechnical Laboratory, 1-1-4 Umezone, Tsukuba 305-8568 Japan.

Presenting Author: Y. Kodama

Cu_1-xBa₂Ca_n-1Cu_nO_y (n = 3, 4, ...) superconductors have excellent features, for example higher T_c of 117K, low superconducting anisotropy, include no toxic elements, etc. But they synthesized under GPa order pressure condition. To use them as practical use, lower pressure synthesis method is required. To search a route to low pressure synthesis, we investigate the stability of Cu_1-xBa₂Ca_n-1Cu_nO_y under several atmsphere.

Sample of Cu_1-xBa₂Ca_n-1Cu_nO_y was synthesized by high pressure method using cubic anvil apparatus with nominal composition of Ba:Ca:Cu:Ag = 2:3:4:0.2. Stability was examined under Ar gas or Ar 80% + O₂ 20% mixture gas atmosphere, pressure of 5 - 50 MPa, with temperature of 400 - 700 ° C using O₂-HIP apparatus.

In the case of Ar 80% + O₂ 20% mixture gas with the pressure of 10MPa, superconducting diamagnetization was almost constant up to 450 ° C. Above 500 ° C, that was decreased with increasing temperature. At 660 ° C superconductivity was disappeared. Although T_c's were constant at 117K.

1PO3-96 Quasi-One-Dimensional Simple-Chain Compounds A_1-xCuO₂ (A=Sr,Ca,Ba) Synthesized at High Oxygen Pressure

Janusz Karpinski 1, Serguei Kazakov 1, and Gerhard I. Meijer 2. 1 Solid State Physics Laboratory ETH 8093 Zurich, Switzerland. 2 IBM Research Division, 8803-Ruschlikon, Switzerland.

Presenting Author: J. Karpinski

All high-T_c superconductors found so far contain two-dimensional (2D) CuO₂ planes. A possible way to modify CuO₂ planes is by an application of high oxygen pressure, which results in the quasi one-dimensional structure of edge sharing chains of CuO₄ squares. We have synthesized three members of the one-dimensional A_1-xCuO₂ family: Ca_0.83CuO₂, Sr_0.73CuO₂ and Ba_0.66CuO₂. Structures of these compounds contain square planar CuO₄ units forming edge-sharing infinite-chains. Sr, Ca or Ba atoms are incorporated between the CuO₂ layers. The Cu ions are coupled by 90° Cu-O-Cu bonds. The formal valence of Cu is +2.34, +2.54 and +2.66 for Ca_0.83CuO₂ Sr_0.73CuO₂ and Ba_0.67CuO₂ respectively. Since electrical resistivity measurements reveal that the materials are insulating, the holes are considered to be localized. Specific heat, elastic and inelastic neutron scattering of polycrystalline material and magnetic torque on single crystals have been measured. An aniferromagnetically ordered state of long-order 3D character exist at T<10K for all three compounds. The spin dynamics of Sr_0.73CuO₂, measured by inelastic neutron scattering, indicate that this ordered state coexists with dimerized singlet ground state.

1PO3-98 High-Pressure Synthesis of Oxyfluoride Superconductors, Sr₂Ca_n-1Cu_nO_2n+dF₂ (n=4,5)

Tetsuya Kawashima, and Eiji Takayama-Muromachi, National Institute for Research in Inorganic Materials, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan

Presenting Author: T. Kawashima

We have already reported the series of high-pressure stable oxyfluoride superconductors, Sr₂Ca_n-1Cu_nO_{2n± d}F₂ (02(n-1)n-F; n=2~5). However, detail investigation of n=4,5 members aren't carried out and their T_c aren't optimized. In this series, T_c is dependent on the oxygen and fluorine contents. To investigate this point in detail, we prepared the samples of n=4,5 members having different oxygen and fluorine contents under high pressure.

Starting materials for high-pressure synthesis were SrF₂, SrO₂, SrCuO₂, Ca₂CuO₃ and CuO. These materials were mixed in an agate mortar to obtain starting mixtures for high-pressure synthesis. The mixture was sealed in a gold capsule and allowed to react in a flat-belt-type high-pressure apparatus at 5.5 GPa, and at 1250 ° C for 3 hours, then quenched to room temperature.

In the presentation, we'll report about the data of lattice constants, the relation of T_c vs. oxygen (or fluorine) contents, optimized T_c value and so on.

1PO3-99 High Pressure Synthesis of Ca-doped Pr-123 Superconductors

K.Q. Li, Y.S. Yao, D.H. Cao, G.C. Che, S.L. Jia, Y.M. Ni, C. Dong, and Z.X. Zhao, National Laboratory for Superconductivity, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China

Presenting Author: K.Q. Li

New superconducting cuprates, Ca-doped Pr-123 system, have been synthesized successfully under high pressure. The compound crystalize in the tetragonal structure. Electrical resistivity and magnetic susceptibility measurement indicate the superconductivity with the transition temperature as high as 115K. This indicate that carrier-doping and proper synthesis route can effectively induce superconductivity in the Pr-123 system.