Jiro Tsujino

Superconducting YBa 2 Cu 3 O x films prepared on YSZ polycrystalline substrates by rf thermal plasma evaporation

As-grown YBa 2 Cu 3 O x films prepared on single crystal (100)MgO substrates by rf thermal plasma evaporation have the advantages of a high deposition rate of 730 nm/min, a large area deposition over 300 cm 2 , and a high J c of 6.8 × 10 5 A/cm 2 (77 K, O T), as reported in previous papers. 1,2 We report in this paper about the preparation of YBa 2 Cu 3 O x films on yttria-stabilized zirconia (YSZ) polycrystalline substrates for a practical application using this technique to synthesize these films on flexible (metal or flexible polycrystal) substrates. Films prepared on YSZ polycrystalline substrates grew with a c -axis orientation at a relatively high deposition rate and exhibited a zero resistance temperature ( T cO ) of 88 K and a critical current density J c of 3500 A/cm 2 (77 K, O T). Films prepared on flexible YSZ polycrystalline tapes with a length of 100 mm were also grown with a c -axis orientation and exhibited TcO ) over 77 K.

Growth Mechanisms of YBa2Cu3O\ssmbix Films Prepared by RF Thermal Plasma Evaporation

YBa2Cu3Ox films prepared by rf thermal plasma evaporation exhibited spiral growth in a wide range of deposition conditions from observations by atomic force microscopy (AFM). However, surface morphology, for example, step width (λ), grain size, and grain shape, varied with deposition conditions. Because surface morphology is affected by growth mechanisms, growth mechanisms can be elucidated by analyzing the change in morphology with deposition conditions. In this study, we investigated the relationship between λ and deposition conditions from a viewpoint of supersaturation. As a result, λ increased with increasing substrate temperature and decreasing raw powder feeding rate, decreasing supersaturation in both cases. In addition, the change in λ and growth rates was explained well by the change in supersaturation using a model based on the BCF theory.

Growth mechanisms of YBa2Cu3Ox films prepared by RF thermal plasma evaporation

We prepared YBa2Cu3Ox films on (100)MgO and (100)SrTiO3 substrates by rf thermal plasma evaporation, and investigated growth mechanisms of these films by observation of the surfaces using an AFM technique. As a result, 2-D nucleation and further coalescence between vicinal grains were observed in the initial stage of growth. In the films prepared for deposition time of 3 min, the different complex growth modes including spiral. growth, “birth & spread” growth, and 2-D growth were observed, which might be due to high growth rate over 55 nm/min of this process.

Optical spectroscopic study of the radio-frequency oxygen thermal plasma evaporated YBa2Cu3O7-x

Optical emission spectroscopy of the rf thermal plasma evaporated YBa 2 Cu 3 O 7− x has been investigated. The deposited films with the nearly stoichiometric composition could be obtained by using Y-rich powder. From the optical emission spectra, O, Y, Y + , Ba, Ba + , Cu, and YO as the emitting species were observed. The excitation temperature was lower for Y + than for the other dissociated elements. The relative intensity for YO of a suboxide became larger with a lower plasma torch. It is thought that the deposited film that is poor in Y results from YO sticking to the substrate rather than Y or Y + .

Step Growth of YBa 2 Cu 3 O x Films Prepared by RF Thermal Plasma Evaporation

We prepared YBa2Cu3Ox films on (100)SrTiO3 substrates by RF thermal plasma evaporation, and investigated growth mechanisms by observation of the surface using AFM and so on. About the films prepared for deposition times of 5 – 180 sec, 2D multiple nucleation was shown in the films for 5 sec and growth modes changed from 2D nucleation, and lateral growth in the initial stage further to spiral growth with deposition times. Accordingly it was considered that supersaturation of this process is high enough to occur frequent 2D nucleation but not clear about the reason why transition from 2D nucleation to spiral growth occur. However, since little tilt between vicinal grains are observed in the film for 30 sec, coalescence of these grains in the initial stage may be an origin of the spiral growth. Moreover, we tried to summarize growth process from initial stage to thick films in this method.

Synthesis of YBCO films on (100)YSZ by rf flash plasma evaporation

Rf flash plasma evaporation is a novel deposition technique which includes the following steps, injecting raw material powders into very high temperature radio-frequency plasma, evaporating fed powders, and deposition onto the substrate surface. We have tried to deposit YBa2Cu3O7-x films on (100)YSZ substrates by using this method. Iijima et al. obtained very high Jc YBa2Cu3O7-x films on an in-plane aligned YSZ intermediate layers on polycrystalline Ni-based alloy substrates by pulsed laser deposition method.[1] Now we are investigating an optimum condition for synthesis of the applicable high Jc YBa2Cu3O7-x films by this unique rf flash plasma evaporation method. In this work we report the obtained relation between the growing crystal orientation and the basic two processing parameters of the substrates’ temperatures and the raw material powder feeding rates. Films were analized by XRD, SEM, and Jc measurements by the conventional four-probe method. We found the results that the films tended to have c-axis orientation as the deposited substrate temperature increased and the raw material powder feeding rates became lower. And we have already had the results that the films tended to have in-plane aligned c-axis orientation as the substrates’ temperatures were higher.[2] Accordingly, these two basic processing parameters of the substrate temperature and the raw material powder feeding rate were turned out to be very important for synthesis of good high quality crystalline YBa2Cu3O7-x films with high Jc. So far we have obtained Jc of 6.6×104 A/cm2 at 77K,0T, but 2.6×104 A/cm2 at 77K,0T, in this work.

Synthesis of Superconducting Oxide Film on Metal Substrate by Radio-Frequency Plasma Flash Evaporation

Radio-frequency plasma flash evaporation is a new deposition technique which includes the following steps, injecting raw material powders into very high temperature radio-frequency plasma, evaporating the fed powders, and deposition onto the substrate surface. We tried to deposit YBa2Cu3O7-x on (100)MgO substrates by this technique and obtained the high Jc films with 6.8×105A/cm2 at 77K,0T. In order to obtain long high Tc superconducting tape wire and large area magnetic shielding, we first attempted to synthesize high Tc superconducting films on metal substrates by this technique. For the first step, we make an attempt to deposit a YSZ intermediate buffer layer on hastelloy substrate by this technique and YBa2Cu3Oy-x on it successively.