ELSEVIER Physica C 265 (1996) 283-294 PHYSICA ® Properties of cobalt-doped YBa2CU3OT_ thin films Brian Moeckly *, Kookrin Char Conductus, Inc., 969 West Maude Ave., Sunnyvale, CA 94086, USA Received 28 March 1996; revised manuscript received 15 May 1996 Abstract We show that the properties of YBa2(Cul_xCOx)307_ ~ films (x = 0 to 0.14) deposited by pulsed laser ablation are sensitive to the growth conditions. We describe the behavior of T c, p(T), Jc(T), and X-ray measurements as a function of cobalt content and deposition parameters. Over a range of deposition parameters for which these properties of undoped YBa2Cu30 7_ ~ are hardly altered, the values for cobalt-doped films may vary greatly. We explain this behavior in terms of the way cobalt is incorporated into the films, thereby altering their structural and transport properties. 1. Introduction In order to learn about the physics and the struc- ture/property relationships of the high-T c cuprate YBa2Cu 307_ ~ (YBCO), it has been crucially impor- tant to study the effect of introducing dopant ele- ments into the structure. These substitutions have included primarily the rare and alkali earths for Y and Ba, transition and noble metals for Cu, and halogens for O. Incorporation of even small amounts of some of these dopants can severely alter the carrier concentration and the normal-state properties as well as destroy superconductivity. These effects should depend not only on which dopant material is chosen and on which lattice sites it occupies but also on how uniformly the dopant atoms are arranged in the crystal structure and how they bond to or affect the arrangement of oxygen, the element in undoped YBCO whose content and distribution drastically * Corresponding author. Fax: + 1 408 523 9999. alters this material's structural and transport proper- ties. The nature of doped YBCO can therefore be quite sensitive to the technique used in sample preparation. There is also a growing cognizance that progress in the technological development of the high-T c compounds, while heretofore substantial, stands to benefit from using doping techniques as a method to tailor materials for use in specific applications. For example, in the thin-film arena, it is possible that the use of dopants may improve the growth habit, mor- phology, stability, noise properties, or current-han- dling capability of passive or active devices. These results may be achieved through the dopant's ability to alter the material's defect structure and transport mechanisms. It has become clear that the control of interfaces between YBCO and other materials is critical in obtaining useful films, multilayers, and junction structures [1,2]. Doped YBCO may be useful in controlling or altering this material's intrinsic inter- faces (i.e., grain boundaries, twin boundaries, etc.). 0921-4534/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved PII S0921-4534(96)00330-9