The effect of YBa 2Cu 3O 7− x target properties on the superconducting characteristics of laser ablation deposited thin films

Abstract

Pulsed-laser deposition has been demonstrated to be an advantageous technique for producing high-quality superconducting YBCO thin films. In this technique, the quality of the YBCO thin films is strongly dependent on various processing conditions such as substrate temperature, laser energy density, ambient oxygen pressure, and pulse repetition rate, all of which have been previously investigated. However, it has been also found that the laser target is one of the key factors in the fabrication of high-quality YBa 2Cu 3O 7− x (YBCO) thin films. In the systematic identification of this effect, nine different YBCO targets have been studied. Both the YBCO targets from various sources and the corresponding YBCO thin films deposited under optimized conditions have been characterized and compared by their structure, composition and electronic properties. This investigation has indicated that impurity phases (liquid phase, 211 and CuO) in the targets play different roles, though the sintered targets as a whole were stoichiometric. The superconducting transition temperature ( T c) of YBCO thin films decreased as the liquid phase (BaCuO 2CuO, which is yttrium deficient) in the YBCO bulk target increased. T c of the thin films may also be decrease with the presence of the 211 phase in the targets, however, the CuO phase in the YBCO target may actually increase T c of the thin films.