Processing Study of Low-temperature Fabrication of EuBa2Cu3O7−δ Film by Transformation from EuBa2Cu4O8 Film Deposited Using the Molten Hydroxide Method

EuBa2Cu4O8 (Eu124) films were deposited on SrTiO3 (100) substrates using the molten hydroxide method and the eutectic composition of NaOH-KOH. The starting materials are a mixture of Eu2O3, BaO2 and CuO. The starting materials and SrTiO3 (100) substrates were put into molten NaOH-KOH at 475°C and kept for 12 h. After cooling in the furnace, substrates were extracted from solidified flux and washed using water and ethanol. The epitaxial Eu124 films obtained were heat-treated and decomposed at 550–825°C and P(O2)=2.0×10–1–1.0×10–5 atm in order to obtain the EuBa2Cu3O7−δ (Eu123) phase. Two-dimensionally aligned Eu123 film was formed on the SrTiO3 (001) substrate at 625°C using the decomposition process of Eu124 epitaxial film grown from molten hydroxide at 475°C. The transformation temperature from Eu124 to Eu123 decreased as the oxygen partial pressure during heat treatment decreased. Cu-rich particles and regions with a diameter of about a micron were precipitated on/in the Eu123 matrix of the decomposed film, and observed by SEM/EDS images. The films decomposed in P(O2)=10−4 atm at 625°C showed Tc=93 K by ρ-T measurement.