Kenichi Tsukada

Metal organic deposition of epitaxial Y123 films using a low-cost vacuum technique

Epitaxial YBa/sub 2/Cu/sub 3/O/sub 7/ (Y123) films were obtained by metal-organic deposition (MOD) using a simple, low-cost vacuum technique without gas flowing. The total pressure and oxygen partial pressure in the furnace were controlled to be 10 kPa and 10 Pa, respectively, by evacuation with a rotary pump followed by refilling with a mixture of O/sub 2/ and N/sub 2/ (O/sub 2/ content: 1000 ppm). XRD analyses exhibited that c-axis-oriented epitaxial Y123 films have successfully been obtained on CeO/sub 2/-buffered YSZ (100) (CbZ) and CeO/sub 2/-buffered sapphire (012) (CbS) substrates. In-plane alignments of these films were as high as that of the CeO/sub 2/ buffer layer. The film on the CbZ demonstrated a high critical current density J/sub c/ of /spl sim/2.1 MA/cm/sup 2/ at 77 K all over the film; the fluctuation of J/sub c/ being within /spl plusmn/10% of the average. Inductive T/sub c/ measurement showed a very sharp peak with T/sub c/=90.5 K. Inductive-J/sub c/ and T/sub c/ of the Y123 film on CbS were 1.1 MA/cm/sup 2/ and 89.6 K, respectively, whereas the T/sub c/ of the Y123 film on LaAlO/sub 3/ was lower than 77 K owing to the occurrence of the a-axis grains.

Synthesis and Properties of Highly Conductive Thin Films as Buffer Layer from Sol-Gel Process

We prepared epitaxial growth SrRuO3 thin film on LaAlO3 (001) (LAO) single crystal substrate and highly oriented BaTiO3 ferroelectric thin film on the epitaxial SrRuO3 thin film. A homogeneous precursor solution for preparing SrRuO3 thin film was prepared with Sr(O—i—C3H7)2 and Ru(NO)(NO3)3 as starting materials, and 2-methoxy ethanol as solvents. The as-coated thin films were heat treated at temperatures from 723 to 1273 K for 1 h in air. SrRuO3 grew epitaxially on LAO(001) substrate, which were confirmed by XRD theta-2theta method and XRD pole figure analysis. The crystallographic relationship of the film and substrate was SrRuO3(001) parallel to LAO(001) and SrRuO3[110] parallel to LAO[100]. A homogeneous precursor solution for preparing BaTiO3 thin film was prepared with Ti[O—n—(CH2)3CH3]4 and Ba(OCOCH3)2 as starting materials, and acetic acid, 2-methoxy ethanol. SrRuO3 coated LAO substrates were coated by spin-coating method with the coating solution. The as-coated thin films were heat treated at temperatures from 973 to 1173 K in air. It was confirmed that the thin films were growing orientated for c-axis by measurement of XRD theta-2theta method.

Preparation of Double-Sided YBCO Films on LaAlO 3 by MOD Using Commercially Available Coating Solution

The 5-cm-diameter double-sided YBa 2 Cu 3 O 7 (YBCO) films were prepared by metal organic deposition (MOD) using a commercially available metal-naphthenate coating solution. Firstly, YBCO film was prepared by MOD on one side of a double-side-polished 5-cm-diameter LaAlO 3 substrate. Secondly, another side was similarly coated with YBCO by MOD. After the latter processing, degradation of average J c value in the first side was not observed; but the fluctuation of critical current density J c slightly increased. The double-sided YBCO films showed average J c values of 0.8-1.0 MA/cm 2 at 77 K and microwave surface resistances R s (12 GHz) of 0.86-1.07 mΩ at 70 K.

Fabrication of Double-Sided YBa 2 Cu 3 O 7 Films on CeO 2 -Buffered Sapphire Substrates by MOD Process

Double-sided YBa 2 Cu 3 O 7 (YBCO) films were successfully prepared on 50-mm-diameter CeO 2 -buffered sapphire substrates by metalorganic deposition (MOD) process using an acetylacetonate coating solution. Mapping analysis of superconducting current densities (J c ) at 77.3 K revealed that J c values of the double-sided films indicated in excess of 2 MA/cm 2 in the center parts with a small decrease of J c at the outer side of the specimens. The J c values of one side (A) are higher than those of the other side (B). Microwave surface resistance (R s ) of sides A and B of the film exhibited 0.57 and 0.60 mΩ, respectively, at 70 K (12 GHz). The difference in the R s values should be attributed to the slight difference in the J c values, which arose from the surface morphology of the CeO 2 buffer layer and heat treatment conditions during the firing process in MOD.

Ferroelectric Properties of (001)- and (106)-Oriented SrBi2Ta2O9 Epitaxial Thin Films

Epitaxially grown SrBi2Ta2O9 (SBT) thin films with (001) and (106) orientations were prepared on La-doped SrTiO3 (001) and (110) substrates, respectively, by coating-pyrolysis process. When the films were annealed in air, their epitaxy was poor and no significant difference was observed in the P-E characteristics for the films that have different orientations. By contrast, the crystallinity and epitaxy of the films increased with decreasing oxygen partial pressure, p(O2), of annealing atmosphere. Using these high quality epitaxial films, we observed a distinct difference in P-E hysteresis curves, which reflects the orientation of the films. After postannealing of these films in O2 to compensate for possible oxygen deficiency, which might have been introduced into the SBT films owing to low p(O2) annealing, the anisotropy of the ferroelectric response was maintained and almost the same P-E loops were obtained.