Texture and transport in spray pyrolyzed TlBa₂Ca₂Cu₃O₉ thick films

Abstract

The electron backscattering pattern technique has been applied to the microstructural investigation of Tl(1223) thick films formed by vapor-phase thallination of Ag-containing Ba–Ca–Cu–oxide precursors. For samples grown on polycrystalline YSZ, considerable biaxial alignment is found in localized, multigrain regions as wide a 100 μm or more. However, on scales above 1 mm the overall texture remains only uniaxial with the c-axes (i.e., [001]) aligned perpendicular to the plane of the substrate. On single-crystal KTaO3 an epitaxial relationship is evident which persists to the surface of a 3 μm thick film. Modest variations in the processing protocol yield films containing grains oriented with the c-axis in the plane, resulting in the degradation of transport properties. The data suggest a growth mode in which sparse nucleation occurs at the substrate followed by rapid lateral crystallization.

Tl-based superconductors for high-current, high-field applications

“…Results concerning the colony structure were confirmed recently by Tkaczyk et al [16] for similar Tl-1223/YSZ films investigated on microstructures of length scales below that reported for the x-ray data. They prepared three types of films differing in precursor thallination protocol, i.e.…”

“…The microstructure of the Tl-1223/YSZ films mentioned previously has been studied by Miller et al [69], Kroeger et al [18], Specht et al [19,20] and Tkaczyk et al [16]. SEM and TEM studies performed by Miller et al [69] revealed the brick-wall structure of these films on macroscopic scale non-epitaxial poly-crystalline thick-films, which may be partially responsible for the high J c values.…”

“…Substantially more efficient in this respect is the open approach. It has been shown that the single-layer polycrystalline T1-1223 films may be grown on poly-crystalline YSZ and Ag substrates with J c values above 10 5 A cm −2 at 77 K/0 T and above 10 4 A cm −2 at 77 K/0.5 T with a field orientation parallel to the crystal c-axis, B c [14][15][16][17].…”

“…The very detailed microstructure studies of polycrystalline Tl-1223 films deposited on poly-crystalline YSZ substrates by spray pyrolysis [14,16] revealed that the film structure consists of 'colonies' of aligned grains [18][19][20]. The colony size is of the order of 0.1-1.0 mm, and each colony consists of about 10 4 grains aligned bi-axially (c-and a-axis alignment).…”

“…In this case [49], SEM micrographs taken of the highest J c samples revealed a highly textured structure consisting of plate-like crystals. However, from the point of view of power applications, the best properties were reported for poly-crystalline 1223 films prepared on YSZ substrates via the reaction of Ag-containing spray-deposited BCC-oxide with Tl 2 O vapour in a two-zone reactor (T c = 104-107 K, J c up to 1.1×10 5 A cm −2 at 77 K/0 T, or J c = 10 5 A cm −2 at 4.2 K/9 T) [14,16,69] and for 1223 films of T(B, S)CCO systems prepared on SrTiO 3 covered by a thin Ag-layer. The most impressive properties are for 1223 films prepared on commercial and special Ag-tape (table 2, number 3 and 8) [17,21].…”