ELSEVIER PhysicaC 265 (1996) 1-4 PHYSICA Effect of thallium oxide, T1203 on the formation of superconducting HgBaCaCuO films A. Brazdeikis a,,, A.S. Hodstrbm a, I. Bryntse b a Department of Physics, Materials Physics, Royal Institute of Technology, S-IO0 44 Stockholm, Sweden b Department of Inorganic Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden Received8 March 1996;revisedmanuscriptreceived17 April 1996 Abstract We show that a small doping of T1203 in the bulk material significantly promotes the formation of superconducting HgBaCaCuO films during encapsulated post-annealing. We also demonstrate that by using this method good quality superconducting HgBa2CaCu206+ s films can directly be prepared using Hg-free thin film precursors. As-prepared films display a strong (001) texture, layer-by-layer growth surface morphology and exhibit superconducting transition tempera- tures, Tc,zero'S as high as 117 K as determined from magnetic and electric transport measurements. 1. Introduction Interest in Hg-based superconducting cuprates [1-2] as candidates for thin film applications has increased rapidly after reports on high critical current densities of the order of 105 A/cm 2 at 110 K in thin HgBa2CaCu20 ~ (Hg-1212) films [3] and the devel- opment of grain-boundary junctions and SQUIDs operating above 110 K [4]. There are, however, severe challenges associated with the development of thin HgBaCaCuO films. In particular, the high toxic- ity and volatility of Hg greatly complicates the use of vacuum deposition. Methods which have been successfully used to produce superconducting HgBa- CaCuO films include magnetron sputtering and laser * Correspondingauthor. Fax: +46 8 249131; c-mail: audrius@matphys.kth.se. ablation from single or multitargets [5-13] followed by high temperature post-annealing. All these meth- ods utilize thin precursor films which are typically deposited at low substrate temperatures and contain both HgO and stoichiometric amounts of BaO, CaO and CuO. The best superconducting films are ob- tained by using a two-target laser ablation and thus mixing on an atomic scale HgO and Ba2CaCu2Ox through layered deposition and subsequent post-an- nealing [8]. All efforts [5,13] to use Hg-free thin film precursor methods have failed to produce both super- conducting and electrically conducting films. Clearly, there is a need for other synthesis methods to be explored. In this paper, we show that a small amount of Tl20 3 significantly promotes the formation of super- conducting HgBaCaCuO films when added to the bulk material during encapsulated post-annealing. The presented technique enables the use of a rather 0921-4534/96/$15.00 Copyright© 1996ElsevierScienceB.V. All fights reserved PII S0921-4534(96)00272-9