SM-BA-CU-O FILMS GROWN AT LOW-TEMPERATURE AND PRESSURE

We have fabricated Sm-Ba-Cu-O thin films at 550-850-degrees-C and at oxygen pressures of 1.2-6.0 x 10(-5) mbar in the presence of ozone. Various groups have reported on the existence of a solid solubility region in bulk Sm1+xBa2-xCu3Oy made at atmospheric oxygen pressure and 975-degrees-C. For these conditions, the superconducting transition temperature, T(c), is known to drop to zero as x is increased from 0 to 0.5. In contrast, we find hardly any decrease of T(c) in our films in the range 0<x<1 and 750-degrees-C < T(growth) < 800-degrees-C, with T(c)'s about 90 K, from which we conclude that the solid solubility is strongly reduced or absent at low oxygen/ozone pressure in this growth temperature range. For this range of composition and growth temperature, we also observe no change in the c-axis lattice constant. The growth temperature that is needed to obtain a film with T(c,0) above 80 K equals 750-degrees-C, which is roughly 100-degrees-C higher than in the case of Y-Ba-Cu-0 films grown under comparable conditions. These results are discussed using thermodynamic equilibrium data of RE1+xBa2Cu3Oy (RE=Y, Sm, La). At low temperature on a SrTiO3 substrate we observe an I-centered cubic phase.