In the previous investigation, the development of REBa2Cu3Oy coated conductor (REBCO-CC) was promoted by using multi insulative buffer layer to restrain metallic element diffusion from the metallic tape substrate and to improve crystal orientation. Consequently, depositing of high-cost Ag layer to stabilize and protect from damage due to quenches are needed, and then it is difficult for production of REBCO-CC to lowering of overall cost. Recently, Doi et al suggested the novel REBCO-CC without Ag stabilizing layer structure, which substituted conductive buffer layer such as Nb:SrTiO3 and Nb:TiO2 for insulative buffer on Ni-electroplated Cube-textured Cu tape.
On the other, we suggested the production method of REBCO film via low-temperature molten alkaline hydroxide, is called “KOH flux method”. The KOH flux method can grow the biaxially crystal-aligned REBCO film on single crystalline substrate at below 500°C. Therefore, it is prospective technique for production of REBCO-CC to cost lowering. Moreover, recently we succeeded in the low-temperature fabrication of LRE–Ni–O (LRE = La, Nd) compounds by KOH flux method. The LRE–M–O compound has a conductive property in particularly case, accordingly, applying LRE–M–O layer to conductive buffer layer is expected. Conclusively, we can suggest that the novel technique for production of whole REBCO-CC by using low-temperature KOH flux method to fabricate conductive buffer layer and REBCO layer are established. In this report, we discussed correlation between depositional condition and obtaining phase, orientation for LRE–M–O films.
For preparing starting materials, LRE2O3 (LRE = La, Nd) and M–O powders were weighed with molar ratios of LRE : M = 1 : 1 and 2 : 1 respectively, and calcined at 1000°C for 24 h. Starting materials, KOH of 400 wt% to starting materials and LaAlO3 single crystalline substrate were put into alumina crucible, and heat-treated at 400–700°C for 12 h. All steps were performed at ambient pressure. After cooling to room temperature, the film and powder samples were extracted from the flux, and the obtained samples were washed by ultrasonic cleaning with distilled water and ethanol to eliminate the KOH and K2CO3. The grown phase, orientation, and lattice parameters were determined by X-ray diffraction (XRD) with a CuKa source. Surface morphology was obtained by optical microscope and scanning electron microscope (SEM).
In the case of La–Ni–O films, the LaNiO3 phase was synthesized at various depositional conditions, although phase stability and orientation deteriorated with increasing fabrication temperature. On the others, Nd–Ni–O films showed that the Nd2NiO4 phase was obtained mainly above 500°C in both Nd : Ni mixture ratios