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 mate-rials with unusual structures or compositions.

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Local structure of infinite layered superconductor Sr₁-xLa_xCuO₂ in low temperature was investigated by EXAFS, X-ray diffraction and Raman spectroscopy. EXAFS showed that the Cu-O bond distance slightly expanded in a range <0.1Å with lowering temperature down to 20K.
The expansion was remarkable below Tc(onset)=43K. Tetragonal lattice parameters shrank with lowering temperature but the shrinkage of a-parameter seemed to be almost saturated below Tc(onset). Oxygen atoms may slightly shift their positions above and below the CuO₂ plane. Raman spectrum of Sr₁-xLa_xCuO₂ superconductors were Raman active although infinite layered structure should be Raman inactive from its symmetry. Resonance Raman peaks were observed at 151cm_-1 and 304cm_-1 in a usage of 4880Å Ar ion laser. Its energy of 2.54eV almost corresponds to that of the exitation between lower and upper Hubard bands. The peak intensities increased with lowering temperature even above Tc(onset). The intensity change may also be related to the change observed with both X-ray absorption and diffraction in local structure with temperature. The CuO₂ plane may buckle as reported in atomic pair distribution function refinement of neutron diffraction data on (Nd.Ce)₂CuO₄ in low temperature.

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SrCu₂O₃ and Sr₂Cu₃O₅ containing two-leg and three-leg S=1/2 ladders made of antiferromagnetic Cu-O-Cu linear bonds, respectively, were synthesized at high pressure, and their crystallographic and magnetic properties were investigated. Susceptibility of the 2-leg ladder system, SrCu₂O₃, showed a thermal excitation from the nonmagnetic ground state with a large spin gap of 420 K, while Sr₂Cu₃O₅ containing 3-leg ladders had a finite susceptibility at the lowest temperature reflecting its gapless nature in the spin excitation spectrum. SrCu₂O₃ has thus been found to be the first 2-leg ladder compound having a well-defined spin gap.

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A cupric oxide carbonate superconductor with a T_c of 92K has been synthesized under high pressure of 6GPa. A single phase sample with a large Meissner volume fraction of 20% is obtained when a mixture with a nominal composition (Ca_0.3Sr_0.7)₃Cu₂ C_0.75 O_y encapsulated with an oxidizer of KClO₄ is treated at 1473K and 6GPa for 30 minutes. The phase crystallizes basically in tetragonal structure with α=3.851Å and c=10.941Å, while an orthorhombic supercell of α×4α×2c forms, most probably as a result of ordering of carbon vacancies along the b-axis. An irreversibility line was measured under magnetic fields up to 5T.

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The perovskite solid solutions, LaFe_1-xCu_xO₃ and LaFe_1-xCu_xO_3-z were prepared under high oxygen pressure and the phase relations and electrical properties were investigated. In the system of LaFe_1-xCu_xO₃, orthorhombic type LaFeO₃ changed to rhombohedral type LaCuO₃ at x=0.6. The electricresistivity of the rhombohedral phase was lower 2 or 3 order in the magnitude than that of the orthorhombic one. In LaFe_1-xCu_xO₃, the oxygen nonstoichiometric samples showed the rhombohedral structure in all x range with metallic conductivity and Pauli paramagnetism. The Seebeck coefficient measurement showed the dominant carriers for x <0.8 are electron, and hole for x>0.8. The perovskite LaFe_1-xCu_xO_3-z is able to have a large amount of oxygen vacancy, where a cubic perovskite like phase having the disordered arrangement is realized.

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We measured complex susceptibilities of Sr-doped YBa₂Cu₃O_7-d superconductors, YBa_2-xSr_xCu₃O_7-d (x=0-1.0) and determined the onset temperature of the superconducting transition. The samples were synthesized by the modified polymerized complex method. With increasing x, the onset temperature decreased, although the depletion was not large as those for Sr-doped YBa₂Cu₄Oy. Measurements of the phonon Raman spectra have revealed that with increasing x the frequencies of the Ba, Cu(2) and apex oxygen O(4) vibrational modes along c-axis change. Besides, at about 570 cm^-1, a small growth of a peak was observed with increasing x, which may be caused by oxygen disorder in the CuO chains. But no appreciable changes in hole density were found from optical absorption spectra.

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Phonon Raman spectra of the modulation-free Bi_1.2 Pb_0.8 Sr₂ Ca_1-y, Y_yCu₂O_z(0.2≤y≤0.8) have been investigated both in polycrystalline and single crystal forms. Polarized Raman spectroscopic measurements of single crystals made it possible to clarify some controversies on the Raman mode assignments for Bi₂ Sr₂ CaCu₂ O_8+d (Bi2212), most notably in high-frequency three prominent oxygen modes observed at 290, 460 and 630cm_-1, which we assigned to A_gO_Bi+B_1gO_Cu, A_g O_Bi and A_g O_{ap _??_ x}, respectively. The energies of the three oxygen modes show drastic change with a decrease of the hole concentration: (1)A_g O_Bi+B_1g O_Cu. mode is shifted towards higher frequencies, (2)A_gO_Bi mode hardly varies for y<0.6, while softens for y>0.6, and A_g O_{ap _??_ x} mode is shifted towards lower frequencies. The observed changes in these oxygen modes are similar to those observed for the modulated Bi₂ Sr₂ Ca_1-y Y_y Cu₂O_z. We propose that the Y/Ca substitution both in the modulated and modulation-free Bi2212 systems induced a hole filling on the CuO₂ plane, which can explain the behaviour of the oxygen modes observed in their Raman spectra.

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The compositional range and the structure of the solid solution of the Pb-added 2212 phase
has been studied in Bi₂Sr_3-xCa_xCu₂Pb_yO_z heated in Ar at 795°C to 822°C. The monophasic compositional range increases as x decreases. For x=1.25 monophasic products with y≤0.6 can be obtained. The structure symmetry changes from tetragonal in y≤0.3 to orthorhombic in y≥0.4. The monophasic compositional range and the Pb-compositional dependence of the lattice parameters in the Pb-added 2212 phase are remarkably different from those in Bi_2-yPb_ySr_1.5Ca_1.5Cu₂O_z reported so far. Tc decreases as y increases.

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Refining behavior due to a small mechanical force and re-formation process of the 2223 phase on heating have been examined for the samples with a nominal composition of Bi_1.8Pb_0.4Sr₂Ca₂Cu_3.2O_z by XRD, TEM, ED, AFM and TG-DTA. The 2223 phase is brittle and easily cleaved at Bi-O double layers in its crystals by a small mechanical force, resulting in changing into the superfine powder with a thickness of 1/2c. On heating the ground powder at 500°C to 800°C in air, various phases were formed from the superfine powder.

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Pining characteristics due to the precipitates of the "3321"(Sr_2.5Bi_0.5Pb₃Ca₂CuO_z) phase have been studied in the Bi-2223 phase in the Bi-Pb-Sr-Ca-Cu-O system by mainly XRD and magnetic measurements. The precipitation of the "3321" phase was controlled by changing annealing temperature and annealing time in air. On annealing at 750°C for 10min and 1h, the larger hysteresis loops in M-H curves were observed in comparison with the initial one before annealing. However, the hysteresis loops became smaller with increasing precipitation of the "3321 " phase. Furthermore, the 2223 phase annealed at 400°C and 500°C, in which no precipitation of the "3321 " phase was observed, exhibits larger hysteresis loops.

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The effect of a combination process with intermediate pressing and sintering on critical current density, Jc, has been studied for the high-Tc Bi system with the nominal composition of Bi_1.6 Pb_0.5 Sr_2.0 Ca_2.0 Cu_3.0 O_z . The Jc of the plate samples has increased drastically from 200 to 2000 A/cm2 by repeating this process more than one time . A micro-hardness Hv, has been measured as a function of the depth from the sample surface . The Hv in the sample has the maximum value of about 80 on the surface and decreases to 50 at depth below 2mm . From the estimation of experimental data, it has been found that the Jc increases exponentially with the Hv.

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Bi(Pb)-Sr-Ca-Cu-O superconducting tubes with different length were fabricated to examine the influence of the length/diameter rate to the magnetic shielding property. As the length/diameter rate increased, the shielding magnetic flux density, at which the flux started to penetrate into the tube center, increased and became constant at length/diameter rate above 1.7. Subsequently, the simulation of the magnetic shielding property was carried with the critical state model. As a result, the simulation result was agreed with the determination result at length/diameter rates above 1.7. However, at length/diameter rates below 1.7. there was differential to the simulation result and the determination result. This is attributed that the tube was not considered as the infinite length tube. Furthermore, the simulation was carried with the Biot-Savart's law. As a result, simulation result of the magnetic shielding property of the tube which contained the short tube, agreed with the determination result smartly.

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Possibility of joining of supercondoctor bulks through laser treatment was discussed. A 4.0×4.5×2.0 mm Bi system bulk was used as the material to be joined. Paste of powder of the same phase, which was dispersed in various kinds of solvents such as distilled water, nitric acid (5wt%), ethyl alcohol and 2-butoxyethyl acetate, was used as the medium material. Two pieces of bulk filled with the medium material between them were installed on a jig system and settled on an X-Y table, followed by laser beam irradiation. A 200 W output CO₂ laser beam accompanied by oxygen gas blow was irradiated onto the medium along the contact line at a speed 10mm/min. The specimen pasted with 2-butoxyethyl acetate show Tc(on) in electric resistance after laser irradiation. SEM images of the joint after laser irradiation reveal improvement of crystallinity. Those results indicate the possibility of connection of superconducting bulks through laser treatment.

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Bi-Pb-Sr-Ca-Cu-O superconducting films were prepared on poly- or single crystal MgO substrate by sol-gel method. For the starting solution, we used acetates-solutes propionic(C₂H₅COOH) or butyric acid(C₃H₇COOH) with or without the addition of aqueous ammonia. The films were prepared by repeating the process of coating and decomposition(at 700°Cfor30 min) 3-10 times and by fin ally sintering at 855°C for 12h. The increase of CH₂ number of solvent and the addition of NH₃⋅H₂O increase the values of pH and viscosity of the solution. These increases make a film twice thickerthan the film obtained from propionic acid solution. For the film sample prepared using butyric acid solution with 6 vol% of NH₃⋅H₂O, the percentage of high-Tc phase was determined by XRD(002) lines to be 40%, which was higher by 7% than that of the film prepared using propionic acid solution. The highest value of Tco(77K) was obtained for the film using butyric acid-NH₃⋅₂0 system.

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We prepared Bi-Pb-Sr-Ca-Cu-O superconducting films on single crystal MgO substrate by sol-gel method. As the starting solution, we used the propionic or butyric acid solution prepared by solving acetates or 2223 phase powder. MgO substrate was coated with the starting solution using a spin coater and heated for 30min at 700°C. This process was repeated several times and the film was heated at 855°C for less than 24h. The film samples obtained from acetates-solute butyric acid were soaked in water or acetone in order to study their effect on Tc_o. The Tc_o of sample soaked for 24h in water was lower by 5K than that of sample before soaking(Tc_o=77K). For the films obtained from 2223 oxide-solute propionic acid, the percent of 2223 phase increased from 0 to 30% when the sintering duration at 855°C increased from 1 to 12h.

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The ingredients of Y₂O₃, BaCO₃, and CuO were treated by a hybridization milling apparatus, pressed at 500kg/cm² and calcined at 925°C for 2 days, followed by annealing at 500'C for 7 days. The milling effects on the samples were inferred from the analysis of the X-ray peaks and SEM observation. It has been clarified that the ingredient materials is very well mixed by milling for 20 minutes, so that the calcined sample may be very good superconductor.

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To assess the alignment of Bi₂Sr₂CaCu₂O_x crystallites for silver sheathed tapes, we analyzed quantitatively the crystallographic textures by using the crystallite orientation distribution functions (ODF). The tapes were prepared from the calcined or completely sintered powder by the powder-in-tube method which involved tubing, drawing, rolling and sintering process. The ODF's were determined from measured incomplete pole figures using the series-expansion method. The c-axis in heavy rolled specimens was inclined slightly from the normal direction of the tapes toward the rolling direction. In the tapes prepared from the calcined powder, the heavy drawn specimens showed a strong preferred orientation in the a -b plane such as (001)[110]. In the case of the sintered powder, heavy rolling led to the remarkable development of textures. The results imply that the ON analysis is necessary for preparation of oxide superconductor tapes.

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Particle shape and particle strength in addition to the powder material, particle size distribution and inter-particle characteristics have great influence upon tap density, densification mechanisms and compressibility of a powder and therefore upon density distribution inside a compact. An attempt is made to investigate the effect of those powder characteristics on constitutive behavior during compaction of powder and thus to incorporate them into constitutive equations developed in the past. Since tap density appears to be a good measure to represent the characteristics of the powder, a new expression that include it is proposed, and the densification mechanism is discussed. It is thus shown by experiment on various copper powders that when the powder is of a narrow size distribution the parameters included in the equation are uniquely determined regardless of the particle shape, i.e dendrytic, irregular or spherical. When particle sizes are widely distributed, on the other hand, they are not determined uniquely. Some of the parameters are the same for all the powders, but they differ from powder to powder and according to the compaction stage.

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Relation between three point bending strength of mullite ceramics and their defects is studied. From SEM analysis of specimens after three point bending test, origin of fracture was mainly due to pores exsisting in specimens. Position of pores depended on specimens and shapes of pores were irregular shapes.Stresses loaded on defects are about 80-90% of bending strengths. Experimental equation of the relation between stress and defect is σ=1420/C^1/2, while σ= 1070/C^1/2 is obtained by Griffith's theoretical equation in case of sphere defect . Maximum mainstress is calculated by FEM on the assumption that shape of defect are oval (radius ratio: a/b). The maximum main stress of oval defect changed about ± 30% in comparison with that of sphere defect in the range of a/b = 0.5-2.0.

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The dimensional changing behavior of the system Fe-2wt%.Cu-0.8wt%C-0.75wt% zinc stearate under an atmosphere of endothermic gas was investigated. The decrease of heating rate causes shrinkage and the decrease of cooling rate causes expansion. On the other hand, the influence of the dew point on dimensional change is also in accordance with tendency of heating and cooling rate. It became clear by two model experiments that the compacts shrink with carburizing during heating and expand during cooling.
In this way, dimensional change depends on carburization, but the behavior observed during heating differs from that during cooling. Authors proposed the new "carbon transfer theory ". When this theory was applied to various sintering phenomena, experimental results could be explained well. In order to solve problems during the sintering process, it must be important to consider the stage where carbon transfer occurrs.

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Ferromagnetic resonance measurements at 34 GHz were carried out to study the magnetic anisotropy field of the acicular Fe particles in the commercially available particulate metal tapes for audio recording. The value of the average anisotropy field due to the acicular shape of the oriented particles has been determined to be 603 kA/m assuming the saturation magnetization (M) of 1.72 T, 80% of bulk Fe. The axial ratio of the acicular particles is 4.8, which is in good agreement with the observed value by TEM. The linewidth of 400 kA/m along the tape length direction is four times as large as that of video Co-y-Fe₂O₃, tapes, which is due to a large distribution of the Fe particle axis.

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