THE EFFECT OF YBA2CU3O7-X TARGET PROPERTIES ON THE SUPERCONDUCTING CHARACTERISTICS OF LASER-ABLATION DEPOSITED THIN-FILMS

Pulsed-laser deposition has been demonstrated to be an advantageous te chnique for producing high-quality superconducting YBCO thin films. In this technique, the quality of the YBCO thin films is strongly depend ent on various processing conditions such as substrate temperature, la ser 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 fab rication of high-quality YBa2Cu3O7-x (YBCO) thin films. In the systema tic identification of this effect, nine different YBCO targets have be en studied. Both the YBCO targets from various sources and the corresp onding YBCO thin films deposited under optimized conditions have been characterized and compared by their structure, composition and electro nic properties. This investigation has indicated that impurity phases (liquid phase, 211 and CuO) in the targets play different roles, thoug h the sintered targets as a whole were stoichiometric. The superconduc ting transition temperature (T-c) of YBCO thin films decreased as the liquid phase (BaCuO2-CuO, which is yttrium deficient) in the YBCO bulk target increased. T-c of the thin films may also decrease with the pr esence of the 211 phase in the targets, however, the CuO phase in the YBCO target may actually increase T-c of the thin films.