Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf Zirconium distribution in solution-derived BaZrO 3 - YBa 2 Cu 3 O 7-δ epitaxial thin films studied by X-ray photoelectron spectroscopy A. Santoni a, ⁎ , F. Rondino a , L. Piperno b , A. Armenio Angrisani c , V. Pinto c , A. Mancini c , A. Augieri c , A. Frolova b , A. Rufoloni c , A. Vannozzi c , N. Pompeo b , G. Sotgiu b , G. Celentano c a ENEA FSN-TECFIS-MNF, Frascati Research Centre, v. E. Fermi 45, 00044 Frascati, Italy b Engineering Department, Roma Tre University, 00146 Rome, Italy c ENEA FSN-COND, Frascati Research Centre, v. E. Fermi 45, 00044 Frascati, Italy ARTICLE INFO Keywords: Yttrium barium copper oxide Vortex pinning Barium zirconate X-ray photoelectron spectroscopy Chemical solution deposition ABSTRACT Superconducting YBa 2 Cu 3 O 7-δ films with different amounts of BaZrO 3 nanoinclusions were deposited on SrTiO 3 (001) by low-fluorine chemical solution deposition with the aim of introducing artificial vortex pinning centres. The Zr concentration over the film thickness could be determined by X-ray photoelectron spectroscopy combined with Ar + ion etching. The Zr/Y ratio has a constant behaviour in the film's bulk. Zr segregation occurs near the surface and Zr diffusion into the substrate is observed near the interface. Conversely, Sr and Ti from the substrate diffuse into the films. Y3d lineshape analysis and X-Ray Diffraction data pointed out that Ti diffusion causes the formation of Y-Ti-O based spurious phases. 1. Introduction The discovery of high temperature superconductivity [1,2] has opened the way for the development of high power superconducting electric devices. Such applications require high critical current densities J c , in magnetic field conditions [3]. YBa 2 Cu 3 O 7-δ (YBCO) is the most promising material for power applications because it can be operated at liquid nitrogen temperature. In type II superconductors as YBCO, J c is ultimately related to the capability of keeping magnetic flux vortices pinned against the Lorentz force F L = J 0 × B 0 exerted by an operating current density J 0 flowing across the sample under applied magnetic field H 0 = B 0 /μ 0 . In YBCO films, lattice defects naturally formed at the growth stage, such as misfit dislocations, oxygen vacancies and segre- gated nano-sized secondary phases can act as pinning centres, whose effectiveness depends on the size, the topology (planar, linear or dots) and the density [4]. More recently, it has been demonstrated that the artificial inclusions of secondary phases of nano-size BaZrO 3 (BZO) into the YBCO film matrix can be achieved in form of nano-rods by pulsed laser deposition or nano-particles by chemical solution deposition (CSD) approaches and with density controlled by the doping level [5,6]. Since then, remarkable improvements in magnetic vortex pinning have been achieved with other artificial pinning centres (APCs) [7]. In par- ticular, BZO has been demonstrated to be very effective for the creation of nanoscale defects in YBCO thin epitaxial films thanks to its chemical and structural stability with YBCO [6,7]. In this work, YBCO epitaxial thin films with different amounts of BZO secondary-phase nanoinclusions have been deposited by chemical solution deposition following the low-fluorine route [8]. The BZO particles are introduced adopting the so-called in-situ approach in which secondary phases are spontaneously formed during the YBCO crystallization thermal treatment. Preliminary work on in-situ YBCO- BZO films had shown a successful formation of a BZO phase but with a degradation of the surface morphology and not optimal critical current J c , likely due to a non uniform Zr distribution. Furthermore, Zr segre- gation has been also reported for nanocomposite YBCO films obtained with an ex-situ approach, which eventually may lead to a non-opti- mized improvement in J c [9]. In this context it is important to de- termine the actual Zr stoichiometry of the grown films as a function of the thickness. To achieve this goal, X-ray photoelectron spectroscopy (XPS) has been used, which proved to have the required sensitivity and accuracy for detecting Zr in small quantities. Furthermore, it will be shown that mild Ar + -ion sputtering does not destroy the film Zr/Y stoichiometric ratio, therefore allowing the acquisition of depth profile data, which can reveal the Zr distribution in the film. 2. Experimental YBCO coating solutions were prepared starting from yttrium (III) https://doi.org/10.1016/j.tsf.2018.11.054 Received 14 December 2017; Received in revised form 16 October 2018; Accepted 27 November 2018 ⁎ Corresponding author. E-mail address: antonino.santoni@enea.it (A. Santoni). Thin Solid Films 669 (2019) 531–536 Available online 28 November 2018 0040-6090/ © 2018 Published by Elsevier B.V. T