Single crystals of oxide superconductor YBa_2Cu_3O_χ have successfully been grown using a slow cooling method where a slight excess of CuO is used in order to make a partial melting condition. Two types of crystals are obtained: block crystals with the aspect ratio of about 0.5, and flake ones with that of about 0.1. The former displays a sharp transition m superconductivity above 90 K, whereas the latter shows a gradual one below 60 K. The former crystals are thought to be made in a condition that solid and liquid phase coexist and a peritectic reaction plays a main role. On the other hand, the latter crystals may be grown under a solution growth condition. Growth condition and mechanism are discussed using the results of microscope observation, SEM-EPMA and quenching experiments.
Single crystals of La-M-Cu-O system (M=Ba, Sr) have been grown by the top-seeded solution growth (TSSG) method with CuO as the solvent. Crystals of approximately 18φ×4 mm in size were obtained. A crystallographic phase diagram for the La_2O_3-CuO system has been derived by means of differential thermal analysis, quenching technique and X-ray diffraction. Single crystal of LaSrFeO_4 has also been grown by the floating zone method, being used as an initial seed crystal.
High T_c superconducting thin films of Ba-Y-Cu-O have been prepared on MgO (100) substrate using ion beam sputtering (IBS) method. After post-deposition oxygen annealing at 920〜940℃, the films exhibited sharp superconucting transitions with T_c endpoint of 79 K. Also annealed films consist of strongly preferred grains with the c-axis perpendicular to the plane of substrate. In this paper we studied the relationship between the superconducting properties and the annealing conditions whereas the latters had a great influence upon the nucleation and growth processes of the 1 2 3 phase. Quite a small amount of Mg diffused from substrates degrades the transition temperature of the annealed films by about 10 K lower than that of bulk ceramics superconductor.
A new compound Er_2Ba_2Cu<1+χ>Pt<1-χ>O_8 (χ≒0.1) was discovered as single crystals. X-ray crystal structure analysis revealed that the crystal structure is orthorhombic (space group: Pcmn) with cell dimensions of a= 10.287 (3) Å, b=5.659 (1) Å and c=13.157 (3) Å, The crystal contains double zig-zag chains composed of Cu, O and Pt ions running parallel to the b axis. A Iarge diamagnetic transition was observed below 80-90 K in the aggregates of the single crystals. However we can not draw, at present, a definitive conclusion as to whether the new compound is really the superconductor or not. Further investigation on the magnetic and electrical properties are now in progress.
Oxygen deficiency of Y-Ba-Cu-O was determined by in situ observation of weight loss in hydrogen atmosphere with thermogravimetry (TG). Oxygen stoichiometry for various phases was found to be as follows: orthorhombic phase (YBa_2Cu_3O_7.0), tetragonal phase (YBa_2Cu_3O_6.23) quenched at liquid nitrogen temperature from 930℃, tetragonal phase with charactor of insulator (YBa_2Cu_3O_6.0) quenched at 645℃ in vacuum (10^-4 mmHg). Amount of oxygen defects of YBa_2Cu<3_χ>Co_χO<7-δ> increases with increasing Co-contents whereas T_c decreases, indicating the valence of Co-ion above 3. Phase transition temperature depends on partial oxygen pressure.
Straight and bent SnO_2 whiskers were grown by oxidizing Sn. Straight whiskers obtained are classified into four types growing in the , ,  and  directions. Bent whiskers are composed of some coherent element whiskers among three types of straight whiskers growing in the ,  and  directions. They usually have a common (011) surface on which isosceles triangular mounds and many steps are seen. The growth direction of the whiskers is easily identified from the orientation of the triangular mound and of the step found on the (011) plane.
Morphology of magnesium particles prepared by evaporation method in argon gas of different purities was studied by electron microscope. As the purity of argon gas became higher, the ratio c/a was increased as well as the value of a, where a and c are respectively the side length and the thickness of hexagonal plates. It was confirmed from the morphology of particles that the purity of argon gas was improved by the gettering action of magnesium particles.