The influence of impurity on the critical thickness of the CeO2 buffer layer for coated conductors

Abstract

The lattice parameters, band structure, density of state and elastic constant of RE-doped CeO 2 (RE=Sm, Gd, Dy), the buffer material for coated HTS conductors, are calculated using the plane-wave method with pseudopotentials based on the density functional theory (DFT) of first-principle. The rule and mechanism of the effect of rare earth impurity on the critical thickness of the CeO 2 buffer layer are investigated. It is found that, in the range of the calculation, the changes of the lattice volume V and elastic constant E* of CeO 2 with the impurity are mainly determined by the increased electrons Δn e of the system. The relationship of the elastic constant E* and increased electrons Δn e is established. It is indicated that the critical thickness of the CeO 2 single buffer layer doped with Sm, Gd, and Dy may be enhanced by 22%, 43% and 33%, respectively.CeO 2 , first principle, critical thickness, elastic constantsSince the first discovery of oxide superconductors in 1986, the research on them in the material science field has proceeded, and the process developments for their applications have also started in recent years. The second generation (2G) high temperature superconducting tapes have considerable potential for large scale power applications because of their ability to carry large in-field current densities, significantly higher compared with the flowing current densities in 1G wire. However, the lack of a reliable and cost-effective process by which 2G tapes can be fabricated in the form of long length has severely hindered their development [1][2][3][4][5] . Many significant efforts for the development of coated conductors (CCs) corresponding to many industrial superconductivity applications have been made in the research fields of oxide superconductors. CeO 2 is considered one of the most effective materials as the buffer layer for CCs, with fine chemistry stability properties and little remarkable chemical reaction with YBCO. In addition, it has the matching crystal lattice with YBCO's [6,7] . Chemistry solution deposition (CSD) may be a promising cost-effective approach for the preparation of the buffer layer of CCs, moreover suitable for the long length tape. However, the thickness of CeO 2 single buffer layer prepared via CSD at present is limited to less than 50 nm [8] , or the micro crack would form in the layer. But the buffer layer thinner than 50 nm could not play the role of the diffusion barrier alone. Therefore, the thickness of CeO 2 film without crack is a significant topic in chemistry solution deposition technique. Recent years, many experiments indicated that RE (lanthanides other than Ce) doping may be an effective approach to improve the critical thickness of solution derived CeO 2 film, which

All Chemical Solution Deposition Route toward REBCO Coated Conductors

“…That is to say, the critical thickness of CeO 2 may be intrinsically modified by Sm-doping. Recent material simulation by Pan et al [20] shows that Sm doping can significantly enhance the Young's Module of CeO 2 at certain doping level due to the modification of the electronic structure near the Fermi level. On the other hand, as reported by Kozuka et al [21], polymer addictive may play as structure relaxing element by retarding the condensation process during the pyrolysis of metal precursors, the result of which is the stress can be partially relieved and the critical thickness be enhanced.…”