Study of correlation between the microstructure and phase inhomogeneities of Y-Ba-Cu-O epitaxial films and their DC and microwave properties

Abstract

The influence of various kinds of structure and phase inhomogeneity on electrical properties of YBCO thin films prepared by inverted cylindrical magnetron sputtering has been investigated. A simultaneous analysis of the changes in the microstructure and electrical parameters has allowed us to define the contribution of each kind of inhomogeneity in the restriction of the film's electrical parameters. It has been found that the transition temperature depends mainly on deviations of the c-axis lattice parameter from its optimum value, the critical current density depends mainly on the out of plane misorientation of the film domains and the microwave surface resistance depends mainly on the volume of the high-angle misoriented domains. By using atomic force and scanning tunnelling microscopy regions of YBCO films with modified properties around Cu-rich second phase particles were observed. It is suggested that superconducting properties of these regions are worse than the matrix due to Cu depletion. Usually the relative area of these inhomogeneities in our films is about 30% and can occupy up to 50% and, therefore, mostly determines the electrical properties of films. It is suggested that the processes of cation disorder deforming the film lattice play an important role in formation of structure and phase inhomogeneities in YBCO thin films.

10.1007/s11455-008-1002-1

“…However, the critical current density in bulk HTSCs (10 4 -10 5 A/cm 2 at T = 77 K) is significantly lower than that in yttrium-based epitaxial films (10 6 -10 7 A/cm 2 at T = 77 K) [3]. This is explained by the more perfect structure of such epitaxial films in comparison to the bulk HTSCs.…”

Nonlinear microwave properties of highTcthin films

“…As one can see, in both cases the film contains a noticeable number of a-axis oriented grains (shown in figure 32(c) in greater detail) and Y 2 O 3 precipitates. However, in the case of low ion energy sputtering the film is smooth and free of outgrowths, whereas in the case of high ion energy deposition the film is rough, Structural images of a magnetron-sputtered YBaCuO film on LaAlO 3 ((c), (d) and (e), TEM images) and a laser-ablated film on CeO 2 -buffered sapphire ((f), optical micrograph) substrates, taken after Kästner et al [47] (reproduced by permission of IOP Publishing Ltd and the authors), (g) AFM image of a YBCO film on YSZ-buffered sapphire substrate, [48] (reproduced by permission of the authors). contains a large number of outgrowths, and also pores and drenches develop throughout the thickness of the film.…”

“…Figure 32. TEM images of magnetron-sputtered YBaCuO films on CeO 2 -buffered sapphire substrate deposited with (a) low and (b) high ion beam energy, respectively, [46] (reprinted from Einfeld J et al 2001 Physica C 351 103, © 2001, with permission from Elsevier).Structural images of a magnetron-sputtered YBaCuO film on LaAlO 3 ((c), (d) and (e), TEM images) and a laser-ablated film on CeO 2 -buffered sapphire ((f), optical micrograph) substrates, taken after Kästner et al[47] (reproduced by permission of IOP Publishing Ltd and the authors), (g) AFM image of a YBCO film on YSZ-buffered sapphire substrate,[48] (reproduced by permission of the authors).…”

Transfer of mass in the growth of Y1Ba2Cu3O7 +Y2BaCuO5pseudo-crystals by a top-seeded growth process

“…It is necessary to grow crystals with a good structure in order to fabricate devices with a high critical current density. For example, the critical current density of epitaxial films Y 1 Ba 2 Cu 3 O 7−δ reaches 10 6 A cm −2 [3]. But j c is much lower in pseudo-crystals [4,5].…”