Thin films of Tl 2 Ba 2 CaCu 2 O 8 (Tl-2212) were grown on LaAlO 3 (001) single crystals by excimer laser ablation using Tl-free Ba 2 CaCu 2 O x targets and subsequent ex situ thalliation. The thalliation process of the film precursor (Ba 2 CaCu 2 O x ) took place in an Al 2 O 3 crucible containing the precursor and Tl-2212 powder. The procedure was carried out at a temperature T a = 820-870 • C and under a reduced oxygen pressure p(O 2 ) = 20-400 Torr. The resulting Tl-2212 films were characterized by XRD, AES, EDAX, ECP, Raman spectroscopy and a.c. susceptibility measurements. The films exhibited epitaxial, c-axis-oriented growth with critical temperatures T c = 98-106.5 K, transition widths T c = 0.5-1 K, and critical current densities at 77 K of j c = (1.2-3.5) × 10 6 A cm −2 . EDAX measurements showed that the films were as a rule somewhat Tl and Ba deficient but Ca rich (Tl 1.7 Ba 1.9 Ca 1.1 Cu 2 O 8 ). AES depth profiling revealed a noticeable depth dependence of the Ca and Ba distribution, though the combined concentration of these elements (Ba + Ca) was fairly constant throughout the whole film thickness. It is postulated that cation disorder (Ba Ca substitution) is responsible, at least in part, for the high critical current density observed in the Tl films. These point defects would contribute to the strong pinning of the flux lines in the films by creating a dense network of pinning centres.

The uniformity of the structural and superconducting properties of lame-area thin films of YBa3Cu-0, IYBCO) deoosited bv RF maanetron swtterina --.on-(OOl) faces of LaA103 single crystals have been investigated king XRD, AES,-SEM, EDAX, Raman spectroscopy and an inductive a.c. method. The YBCO films were deposited over areas up to cz 23 x 23 mm2, and were cz 160&2100 A thick The films were highly c-axis oriented, exhibited Tm = 89 & 1 K, and IC = 1.7-2 f 0.5 x IO6 A c m 2 at 77 K across the entire film area. Raman spectra showed that oxygenation of the films was z ? 6.83, and the degree of epitaxy was q = 88%. EDAX measurements showed a very uniform distribution of Y, Ba and Cu across the film area. Local changes in mosaic spread and the c-axk length, observed near the edges of the films, corresponded with the measured variations in the critical current density &). Reproducible sputtering conditions have been determined for the growth of high-quality large-area YBCO superconducting films.

High-quality SA and S/I/S epitaxial heterostructures (S = YBaaCusO,, I = %TO3) have been grown in situ on LaA103 and SrTi03(OOl) single crystals, by the single-chamber pulsed laser deposition technique. YBa2Cu30, and SrX03 layers were deposited sequentially, at a substrate temperature Th = 760 OC, and an oxygen pressure p(02) = 300 mTorr. Structural data showed that the Srli03 layer, grown either on a YBCO film or sandwiched by two YBaCuO films, was strained in the (001) plane and exhibited an elongation of the lattice parameter in the [OOl] direction. This behaviour was consistent with the epitaxial growth of the SA and S/WS structures as revealed by the MEED and ECP patterns. Ion milling in conjunction with AES analysis showed that the thicknesses of the interfacial regions were 535 A, and resulted from residual roughness of the substrates. The critical temperature (TJ and critical current density (io) of the multilayers at 77 K, as determined by an inductive AC method, were found to be To = 89.5 and 90.5 K. and jo = 3 and 5 x lo6 A for trilayers and bilayers, respectively.