Effects of oxygen partial pressure and substrate temperature on the in situ growth of the Ba1−xRbxBiO3 films by laser ablation

Abstract

Effects of oxygen partial pressure and substrate temperature as well as the Rb content in the target on the in situ growth of Ba1−xRbxBiO3 (BRBO) films prepared by laser ablation are studied. The optimal target composition for growing the superconducting films in the present study is Ba:Rb:Bi=0.6:0.8:1.0. Oxygen partial pressure plays an important role in controlling the doping of Rb into the BRBO phase and hence the growth of the superconducting films. For the Ba0.6Rb0.8BiO3 target the superconducting films can be grown at 410–485 °C in 1–50 mTorr of O2 and the optimal pressure is about 20 mTorr, under which Rb is readily doped into the BRBO phase. Meanwhile the best film with Tc (onset) of 27.5 K and Tc (zero) of 25 K is grown at 475 °C in 20 mTorr of O2. The (100) preferred orientation is present in most of the superconducting films, while the (110) orientation is dominant in the films grown in 30–40 mTorr of O2 at 430–450 °C which are about 100 °C higher than those reported previously. For the superconducting films thicker than 0.6 μm the cracking is commonly observed and the lower the growth temperature the greater the cracking. The degradation of the Tc of the BRBO film on exposure to air (moisture) can be attributed to the surface contamination which may also be one of the causes for the semiconductive behavior of electrical resistivity in the normal state.