Akira Oishi

Microstructures of a -axis oriented YBCO films made by hybrid plasma sputtering

Microstructures of a -axis oriented YBa 2 Cu 3 O 7− x films made by newly developed de 100 MHz hybrid plasma sputtering were investigated using transmission electron microscopy (TEM). The films deposited on (110) NdGaO 3 and (100) SrTiO 3 substrates were found to grow in a perfect epitaxial fashion and with clear interface. The plan view of the TEM image showed that both films were comprised of two kinds of grains having the c axis aligning along two perpendicular directions in the plane with equal probability. The structures of the grain boundary, however, were found to be very different for the two films from the plan views. The film on NdGaO 3 showed a lot of twist boundaries, while the film on SrTiO 3 consisted of many symmetrical tilt boundaries and basal-plane-faced tilt boundaries. The type of grain boundary is determined by the anisotropic growth rates of the film between c direction and a-b direction.

TEM Studies on Microstructure of a-Axis Oriented YBCO Films

The microstructure of a-axis oriented YBCO films made by newly developed dc-100MHz hybrid plasma sputtering was investigated using the transmission electron microscopy. The films employed in this study were grown on (110) NdGaO3 and (100) SrTiO3 substrates and were confirmed to have an excellent crystallinity by X-ray diffraction and Rutherford backscattering measurements. The interface between the film and the substrate was found to be very sharp for both films. From the plan view of the TEM image, both films were found to consist of two kinds of grains having the c-axis aligning along two perpendicular directions in the plane with equal probability. For the film on NdGaO3 substrate, many twist boundaries which has a (100) boundary plane parallel to the surface could be observed, while the film on SrTiO3 had only symmetrical tilt boundaries and basal-plane-faced tilt boundaries, which have (013)(0 \(\bar 1\)3) and (001)(010) planes as boundary plane respectively. The difference can be explained from the anisotropic growth rates of the film between c direction and a-b direction.

Single Phase a-axis YBCO Films Epitaxially Grown on NdGaO3

YBa2Cu3O7−x (YBCO) thin films on NdGaO3 (110) have been prepared using a newly developed DC-94.92MHz hybrid plasma magnetron sputtering. The hybrid plasma was generated by applying a negative bias voltage to the RF cathode. The YBCO films showed an excellent crystallinity with the a-axis being perpendicular to the plane of the substrate. A full width at half maximum (FWHM) value of 0.027° in the rocking curve through the (200) peak and χmin of 3.8% in the Rutherford backscattering channeling measurement were achieved. The interface between the film and the substrate was found to be very sharp by cross-sectional transmission electron microscopy (TEM). The surface of the films were also very smooth.

New Substrate La1−xNdxGaO3 for High-Tc YBa2Cu3Ox Epitaxial Films

La0.66Nd0.34GaO3(LNGO) single-crystalline boules were successfully grown by the Czochralski method. The boules have no crack and few twins. The structure of LNGO is orthorhombic with the lattice constants; aO=5.49lA, bO=5.492A, cO=7.766A. The length of cell-edges along both and are 3.883A, which are close to the length of b-axis or a third of c-axis length for YBa2Cu3Ox(YBCO). YBCO films grown on a (110) plane of these substrate were epitaxial. The crystallinity of the films was very good; the value of FWHM for YBCO (200) peak was 72sec (0.020deg.), which is comparable with that of the substrate.

Superconducting Properties of YBCO Thin Films Deposited on Grainboundary Free Y2O3 Substrates

Y2O3 single-crystal was grown by Verneuil method. The crystallinity (FWHM004 = 61”) is comparable or superior to the other commercial substrates for superconducting films. The crystalline structure is cubic, and there is no phase transition in the range of 77 – 2,570K. The dielectric constant of Y2O3 substrate is smaller than 9, which is comparable to MgO. Not only c- axis, but also a-axis oriented YBCO film have been grown on Y2O3 (001) substrates by control of substrate-temperature like MgO, and SrTiO3. The width of the interface between YBCO and Y2O3 is less than 100A, which indicates the interface is very sharp and stable.

Superconducting Properties of YBa2Cu3OX Films on Y2O3 Single Crystal

The c-axis oriented YBa2Cu3OX(YBCO) film has epitaxially grown on Y2O3(100) substrates by laser deposition for the first time. The orientation of YBCO is parallel to Y2O3 . The critical temperature at zero resistance is 86.2K with a transition width of 1.2K. The critical current densities at 5K was estimated to be 1.4 x107, and 2.0 x106A/cm2 without and with a magnetic field of 5Tesla, respectively.