Heterogeneous nucleation of YBCO via fluorine based MOD process: thermodynamic and kinetic approach

Abstract

The nucleation of YBa2Cu3O7−δ (YBCO) film deposited via metal organic decomposition (MOD) approach is a complex process that has a key role in YBCO film crystalline orientation and, consequently, superconducting properties. Up to now, several studies have been carried out to clarify this step in the fluorine based MOD route which employs only or partially metals trifluoroacetate for the precursor solution preparation. However, these previous works provided only qualitative indications, whereas a quantitative theoretical investigation seems to be still lacking. In this paper, the free energy for critical nucleus formation of fluorine based MOD YBCO has been determined according to the classical nucleation theory. The volume contribution to the free energy is computed using thermodynamic data on (Y, Ba, Cu, O) systems available from the literature. The free energy barrier for nucleation depends upon nucleus orientation, via the work of adhesion and surface energies of vacuum/nucleus interfaces. The model is applied to describe heterogeneous nucleation of YBCO on (001) SrTiO3 single crystal and provides quantitative information on nucleation barriers as a function of temperature and both precursor and gas phase compositions. Through a kinetic approach, the energy barriers are further employed to estimate the fraction of c-oriented nuclei as a function of temperature and water partial pressure. Comparison with experimental data from literature lends support to the proposed computations. Therefore, the results shown in this work may be useful in designing the YBCO deposition process in order to obtain films with superior superconducting properties avoiding expensive and time-consuming experimental optimizations.

Nanodiamond Influence on the Nucleation and Growth of YBCO Superconducting Film Deposited by Metal–Organic Decomposition

“…Otherwise, it could hamper the evolution of BaF 2 toward BaF 2(1– x ) O x (with x ≠ 0). As already evidenced by ref , the x value strongly affects the free energy change of reaction I; thus, at 750 °C and , a reduction of the x value corresponds to a critical increase of reaction free energy, Δ r G , (Figure 2 in ref ). Conversely, at 800 °C and , reaction I is spontaneous in the full x range.…”

“…However, regardless of the reaction mechanism, the excellent morphology of YBCO+ND with improved superconducting properties should derive from the possibility of starting nucleating at higher temperatures, when the best conditions for c-axis nucleation occur. 56 A schematic representation of ND influence on the YBCO deposition process is reported in Figure 14.…”

Effect of Chlorine Addition on Texture and Superconducting Performance of YBa2Cu3O7−δ-Coated Conductors

“…The nucleation modes of thin films mainly include the uniform nucleation and nonuniform nucleation, where uniform nucleation refers to spontaneous uniform nucleation relying on its own structure, while nonuniform nucleation refers to nonspontaneous, inhomogeneous nucleation induced by an external plasma or substrate. Nonuniform nucleation dominates in YBCO films due to the presence of interfacial energy between the substrate and YBCO [17]. For any deposition method, the nucleation growth process of thin films is quite complex and it includes a series of thermodynamic and kinetic processes.…”

An advanced electrical heating technique for double-sided Y(Gd)BCO coated conductor: gaining high engineering current density based on MOCVD

“…Currently, the major methods for the preparation of REBCO HTS films include pulsed laser deposition [9,10], reaction co-evaporation [11,12], metal organic deposition [13,14] and metal organic chemical vapor deposition (MOCVD) [15][16][17]. Due to the need to meet the requirements of double-sided simultaneous deposition and electrical self-heating method, MOCVD is adopted to prepare Y(Gd)BCO superconducting films.…”