Hybrid liquid phase epitaxy processes for YBa₂Cu₃O₇film growth

Abstract

A number of liquid phase epitaxy (LPE) related growth methods have been investigated. These hybrid-LPE processes enable high rate 'liquid assisted' growth of epitaxial YBa 2 Cu 3 O 7 films without the many disadvantages of classical LPE. Growth occurs by diffusive transport of Y through a thin liquid flux layer. This layer may be pre-deposited onto the substrate by various means including vacuum and non-vacuum techniques, or deposited at the growth temperature. The composition of the liquid layer is maintained during film growth by feeding YBa 2 Cu 3 O 7 , or the separate components, either from the vapour or by a powder route. Growth rates up to 10 nm s −1 have been demonstrated. Deposition of c-axis oriented epitaxial YBa 2 Cu 3 O 7 is reported on both seeded and non-seeded substrates; the process is tolerant of a high substrate mismatch. Films 1-2 µm thick with T c ∼ 90 K and a critical current density J c > 2 MA cm −2 have been grown on a range of single crystal substrates as well as on buffered textured metallic tapes. The mechanism of nucleation and growth from a thin liquid layer is described within the general theoretical framework of crystal growth. Particular features of the growth are the short time constant for equilibration of transients in the deposition conditions, the wide range of relative supersaturation spanned by the process, and dominance of interface kinetic effects compared to volume diffusion in the liquid flux.

(RE)Ba2Cu3O7 Coated Conductors for AC and DC Applications

“…The actual deposition of the layers on the metallic substrates can be divided into physical methods and chemical methods as presented in Table 1. All the different types of deposition techniques of buffer and superconductor such as: pulse laser deposition, PLD [6]; ion-beam assisted-deposition, IBAD, [6,7]; sputtering [8], chemical vapour deposition, CVD [9]; metal organic deposition, MOD, [10,11]; metal organic chemical vapour deposition, MOCVD [12]; thermal evaporation [13]; sol-gel deposition [14,15]; ink-jet printing and coating [16]; dip coating [17]; and liquid phase processing [18,19], Tab.1, have been used to manufacture shorter or longer pieces of the high temperature superconducting tapes on a laboratory scale [20,21]. There is an additional aspect to the multifilamentary conductor preparation, which is needed for AC applications [22].…”

“…This can be obtained in most fcc metals by cold rolling to a reduction of greater than about 95% followed by heat treatment [32][33][34]. Cold rolling gives a characteristic, but quite complex, texture described as (110) [112], (112) [111], (123)[422] and (146)[211], Fig.7a), b). (An ideal texture has (hkl) planes parallel to the sheet and the vector [uvw] parallel to the rolling direction.)…”

“…The so-called native oxide buffer layers can be made by direct oxidation of the metallic substrates to simplify the deposition process. Such Ni-O layers are successfully used in LPE processing [18,19]. In the second generation AC conductors for small magnetic field ~ 0.4T, where interfilamentary decoupling is vital, magnetic buffer layer will be introduced [22,40,41].…”

“…In contrast, hybrid liquid phase epitaxy, HLPE growth is controlled by adjusting the rate of feeding of the liquid layer, with RE-rich material at constant temperature (RE)Ba 2 Cu 3 O 7 , growth occurs by RE diffusive transport through a thin liquid BaO-CuO boundary layer); in this case σ, and the corresponding undercooling, adjust self-consistently to match the growth rate to the feeding rate [146]. For steady state growth the flux layer needs to be fed with stoichiometric (RE)Ba 2 Cu 3 O 7 material.…”

“…In addition, the process has a high efficiency of material utilization, and thick films can be produced with excellent crystallinity and high critical current densities. These features suggest that HLPE has the potential to be a robust high-rate low-cost process for coated conductor processing [18,151,154,155].…”