- Email: [email protected]
Growth of YBCO film by chemical solution deposition with an optimization fluorine process
Accepted Manuscript Growth of YBCO film by chemical solution deposition with an optimization fluorine process L.H. Jin, Y. Bai, C.S. Li, J.Q. Feng, L. Lei, G.Y. Zhao, L. Gao, P.X. Zhang PII: DOI: Reference:
S0167-577X(19)30673-1 https://doi.org/10.1016/j.matlet.2019.04.108 MLBLUE 26091
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
24 February 2019 23 April 2019 26 April 2019
Please cite this article as: L.H. Jin, Y. Bai, C.S. Li, J.Q. Feng, L. Lei, G.Y. Zhao, L. Gao, P.X. Zhang, Growth of YBCO film by chemical solution deposition with an optimization fluorine process, Materials Letters (2019), doi: https://doi.org/10.1016/j.matlet.2019.04.108
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Growth of YBCO film by chemical solution deposition with an optimization fluorine process L.H. Jina,*, Y. Baib, C.S. Lia, J.Q. Fenga, L. Leib, G.Y. Zhaob, L. Gaoc, P.X. Zhanga a
Northwest Institute for Nonferrous Metal Research, Xi’an, 710016, China
b
Xi’an University of Technology, Xi’an, 710048, China
c
Xi’an Technological University, Xi’an, 710021, China
Abstract: Trifluoroacetate metal organic deposition (TFA-MOD) with low fluorine contents would bring benefits for the environment and the epitaxial growth of YBa2Cu3Oy (YBCO) film. In this paper, a simple and effective method which could tune the fluorine content and improve the performance of YBCO film was reported. YBCO Low-Fluorine / YBCO Fluorine-Free composites were prepared on LaAlO3 single crystal substrate. During the pyrolysis process, the fluorine would diffuse across the interface of YBCO Low-Fluorine / YBCO Fluorine-Free composites. Both the fluorine in the YBCO Low-Fluorine and the carbon in the YBCO Fluorine-Free could be reduced. It could significantly improve the epitaxial growth and performance of YBCO film. Keywords: YBCO film; MOD; Fluorine * Corresponding author. Email: [email protected].
1. Introduction Chemical solution deposition (CSD) has been successfully employed to prepare YBaCu3Oy (YBCO) coated conductor with high performance. According to the presence of fluorine, CSD routes include trifluoacetate metal organic deposition (TFA-MOD) [1], and fluorine-free (FF) solution route [2]. TFA-MOD shows low cost merits for the scale production [3]. During the heat treatment, the significance
intermediate phase is the formation of BaF2 instead of BaCO3, because the stable BaCO3 can make the weak-link behavior and decrease the critical current density of final YBCO film. However, the conventional TFA-MOD method needs a slow decomposition process which is not suitable for the fabrication of long length coated conductors. The control of fluorine content may offer the possibility of fast pyrolysis process, minor harmful fluorine byproducts, higher grain growth rate and good performance of REBCO film [4]. Hence, the special heat treatment process and the modified precursor solution are developed to tune the fluorine content. The fluorine (F)-free precursors were used as alternatives to prepare low fluorine solutions. The F-free copper naphthenate or copper octylate were also employed as precursors in advanced TFA-MOD process by SRL-ISTEC [5,6]. In our previous work, we have replaced copper trifluoroacetate by copper benzoate or acetate to fabricate homogeneous film in fast pyrolysis process [7,8]. Palmer et al designed low fluorine solutions using different quantities of fluorine and non-fluorine carboxylate precursors with a total amount of fluorine from 10% to 50% [9]. Wu et al synthesized an ultralow fluorine solution to fabricate YBCO film with high performance [10]. And the effect of F/Ba ratio on the properties of the YBCO films was systematically investigated by Bian et al [11]. Furthermore, a large F concentration may produce uncontrollable amounts of BaOF liquid in the thick film. Feenstra et al introduced a medium-temperature anneal process (F-module) between pyrolysis and crystallization to decrease the F concentrations [12]. In this paper, a new method was developed to tune the fluorine content for YBCO film growth. The YBCO Low-F/ YBCO F-free films were prepared from the low fluorine solution (F%=23.1%) and fluorine-free solution (F%=0). The fluorine diffusion from YBCO Low-F layer to YBCO F-free layer is considered to tune the
fluorine and carbon residues. It improves the texture and performance of YBCO film. 2. Experimental For the low-fluorine precursor solution (YBCO-LF, F content = 23.1%) [8], the precursors included yttrium trifluoroacetate (Y(CF3COO)3), barium propionate (Ba(C2H5COO)2) and copper propionate (Cu(C2H5COO)2). In contrast, yttrium acetate (Y(CH3COO)3), Ba(C2H5COO)2 and Cu(C2H5COO)2 were used to prepare the fluorine-free solution (YBCO-FF, F%=0%). All mixtures were dissolved separately in methanol and propionic acid (CH3OH:C2H5COOH = 1:1). The stoichiometry of metallic cations was a fixed value (Y:Ba:Cu = 1:1.5:3). The solutions were heated to 80 oC for 30 min with continuous stirring to obtain stable blue-colored solutions with a total cations concentration of 1.2 mol/L. The LaAlO3 single crystal (LAO, 10 mm × 10 mm) substrate was cleaned in the ultrasonic acetone bath for 20 min. Firstly, the fluorine-free solution was firstly deposited on LAO substrates by spin coating with a spinning rate of 2000 rpm for 2 min. The gel film was pyrolyzed at 450 oC under humidified oxygen atmosphere to form the YBCO-FF/LAO pyrolyzed film. Secondly, the low fluorine solution was coated and pyrolyzed to form YBCO-LF/YBCO-FF/LAO pyroyzed films. Thirdly, the YBCO-LF/YBCO-FF/LAO precursor films were crystallized at 800 oC for 2h in Ar-0.01%O2 atmosphere with 4.2% humidity. Finally, the crystallized films were annealed at 450
o
C for 4 h in a dry oxygen atmosphere to form YBCO
superconducting film with orthorhombic phase. The morphology of YBCO films were characterized by scanning electron microscopy (SEM S-4800), optical microscopy (OM Olympus PMG3) and atomic force microscopy (AFM SPM-9500J3). The chemical states of film were evaluated by X-ray photoelectron spectra analysis (XPS, ESCALAB 250Xi). The phase
composition of film was investigated by X-ray diffraction using CuKα radiations (XRD Bruker D8 Advance). The critical current density (Jc) was determined by VSM (VersaLab, Quantum Design). 3. Results and discussion YBCO precursor films derived from the fluorine-free solution and low fluorine solution were pyrolyzed at 450 oC using the heating rate of 5 K/min to form YBCO-LF/YBCO-FF/LAO. Fig. 1 shows the surface morphologies and x-ray diffraction
patterns
pyrolyzed
films.
The
surface
of
YBCO-FF
and
YBCO-LF/YBCO-FF pyrolyzed films are smooth and homogeneous without carks or wrinkles. It implies that the decomposition stress can be gently released under the relatively
high
ramping
speed.
However,
the
surface
morphology
of
YBCO-LF/YBCO-FF is flatter than that of YBCO-FF. The roughness (Rrms) value of YBCO-LF/YBCO-FF is ~1.84 nm in the scanning area of 5 µm × 5 µm, which is smaller
than
that
of
YBCO-FF
(Rrms =
~5.06nm).
The
roughness
of
YBCO-LF/YBCO-FF is close to that of YBCO-LF precursor film in scanning areas of 5µm × 5µm and 10µm × 10µm (Fig. 1c). The presence of fluorine may promote the uniform decomposition reaction and be beneficial for the acquirement of smooth surface. Fig. 1d gives the corresponding θ-2θ XRD patterns. The peaks of CuO and BaF2 can be observed in YBCO-LF/YBCO-FF pyrolyzed film. Moreover, Ba1-xYxF2+x (BaYF) and CuO phases can be observed in YBCO-LF. The very weak peak ascribed to monoclinic BaCO3 phase can be detected in YBCO-FF. In comparison with the YBCO-LF, there is the unusual formation of BaF2 in the YBCO-LF/YBCO-FF. Y3+ ions may release from BYF phase to form Y-O-F or Y2O3 phase [8]. It indicates that there is fluorine diffusion between the top coating and bottom coating. The formation of BaF2 phase in YBCO-LF/YBCO-FF may be suitable for the ex-situ “BaF2 process”
and useful for the growth of YBCO film. The cross-SEM morphology of YBCO-FF and YBCO-LF/YBCO-FF pyrolyzed films are shown in Fig. 2. The clear interface between substrate and pyrolyzed film can be observed in the samples. The thickness of YBCO-LF/YBCO-FF reaches at ~600nm. The thicknesses of top and bottom coatings are ~340nm and ~260nm, respectively. There is no vertical open porosity in YBCO-LF/YBCO-FF. The composite is less porous than all TFA-YBCO film pyrolyzed under oxygen atmosphere [13]. The composite may be useful for a release of pyrolysis subproducts and a dense precursor film. Fig. 3 shows the XPS of Y3d, Ba3d, Cu2p, O1s, F1s, and depth profile of YBCO-LF/YBCO-FF/LAO precursor film. Y 3d5/2 spectrum shows the split double peaks located at binding energies of ~158.9eV and ~156.7eV (Fig.3a) [14]. It can be ascribed to the presence of Y2O3 and YF3. And there is only minor YF3 phase in the film according to the weak binding energy peak. It can form Y-O-F clusters and is consistent with the XRD analysis of film. Two peaks of Ba 3d3/2 and Ba 3d5/2 energy levels are at binding energies of ~795.4 and ~780.2 eV, as shown in Fig.3b. It represents binding energy of BaF2. Cu spectrum shows two peaks at binding energies of ~932.6 eV and ~952.4 eV (Fig.3c). The peaks are consistent with Cu 2p3/2 and Cu 2p1/2 and the presence of CuO or Cu2O. The spectrum of O 1s presents the maximum peak at ~529 eV with a shoulder peak at ~531.1eV (Fig. 3d). It can be assigned to the binding energies of Y-O and Cu-O compounds. A sharp and intense F 1s peak at binding energy of ~684.2eV can be observed in Fig. 3e. It is consistent with the presence of BaF2 and Y-O-F. F 1s in BaF2, YF3 and CuF2 are typically located at the binding energies of ~683.7 eV, ~685.3 eV and ~685.9 eV, respectively. Hence, the BaF2, Y-O-F and CuO or Cu2O are main phases in the film. The variation of Ba, F, C
elements after Ar+ bombardment are shown in Fig. 3f. F element can be detected in the whole XPS depth profile of YBCO-LF/YBCO-FF. The F content decreases firstly and then increases from YBCO-LF to YBCO-FF. Furthermore, the carbon content can be obviously reduced when fluorine enters into YBCO-FF. It clearly indicates that the fluorine diffuse from the YBCO-LF to the YBCO-FF. Fig. 4 shows the typical θ-2θ scan, scan, ω scan and Jc-B curve of crystallized films. The strong YBCO (00l) peaks without other peaks can be observed in Fig. 4a. It indicates there are only high c-axis preferred orientation grains in the YBCO-LF/YBCO-FF crystallized film. The omega scan of YBCO (005) peak and phi scan of YBCO (103) peak are shown in Fig. 4b and 4c. The full-width at half maximum (FWHM) value of out-of-plane (∆ω) is ~0.9o. The in-plane scan consists of four peaks with the average FWHM value (∆) of ~1.47o. The FWHM value of in-plane scan is comparable to that of YBCO film (∆1.3 o) prepared by the solution with 20% F content [9]. In addition, the FWHM values of ∆ω and ∆are close to the results of LF-YBCO film (∆ω =0.8o and ∆o) [2,15]. It indicates good in-plane and out-of-plane alignments of YBCO-LF/YBCO-FF crystallized film. The dependence of Jc on magnetic field is shown in Fig. 4d. The whole thickness of crystallized film is at ~360nm and the Jc value of YBCO-LF/YBCO-FF reaches at ~3.98 MA/cm2 at 77K, 0T. The Jc decreases rapidly with increasing the applied magnetic field. In the references [2,10,15], the Jc values of 3~5MA/cm2 (77K, 0T) could be achieved in the ~200nm thick LF-YBCO films. And the Jc values decreased obviously to ~2MA/cm2 on the ~450nm thick film. However, in this work, the high performance can be maintained in the thick YBCO-LF/YBCO-FF film. Therefore, this double layer structure may be beneficial for the acquirement of good texture and high performance.
4. Conclusions YBCO Low-Fluorine / YBCO Fluorine-Free composites have been fabricated on LAO substrate by solution deposition method. The simple and effective method is used to smooth the surface, tune the fluorine content and improve the microstructure. The fluorine can diffuse from YBCO-LF to YBCO-FF and reduce the carbon content of YBCO-FF. It contributes to the acquirement of high c-axis preferred orientation grains and sharp texture. The FWHM values of omega and phi scans are ~0.9o and 1.47o, respectively. And the YBCO-LF/YBCO-FF crystallized film shows high Jc of ~3.98 MA/cm2. This method may be beneficial for good texture and high performance of YBCO crystallized film. Acknowledgements This work was financially supported by the National Science Fund Program of China (No.51777172), the Natural Science Basic Research Plan in Shaanxi Province (No. 2017ZDJC-19). References [1] T. Izumi, K. Nakaoka, Supercond. Sci. Technol. 31 (2018) 034008. [2] Y. Zhao, P. Torres, X. Tang, P. Norby, J.C. Grivel, Inorg. Chem. 54 (2015)
10232-10238. [3] M.W. Rupich, D.T. Verebelyi, W. Zhang, T. Kodenkandath, X. Li, Mater. Res. Soc. Bull. 29 (2004) 572-578. [4] P. Cayado, B. Mundet, H. Eloussifi, F. Vallés, M. Coll, S. Ricart, J. Gázquez, A. Palau, P. Roura, J. Farjas, T. Puig, X. Obradors, Supercond. Sci. Technol. 30 (2017) 125010. [5] Y. Tokunaga, T. Honjo, T. Izumi, Y. Shiohara, Y. Iijima, T. Saitoh, T. Goto, A. Yoshinaka, A. Yajima, Cryogenics 44 (2004) 817-822. [6] H. Ichikawa, K. Nakaoka, M. Miura, Y. Sutoh, T. Nakanishi, A. Nakai, M. Yoshizumi, T. Izumi, Y. Shiohara, Physica C 469 (2009) 1329-1331. [7] L.H. Jin, Y.F. Lu, J.Q. Feng, S.N. Zhang, Z.M. Yu, Y. Wang, C.S. Li, J. Alloy. Compd. 568 (2013) 36-41.
[8] L.H. Jin, C.S. Li, J.Q. Feng, Z.M. Yu, Y. Wang, L. Lei, G.Y. Zhao, A. Sulpice, P.X. Zhang, Supercond. Sci. Technol. 29 (2016) 015001. [9] X. Palmer, C. Pop, H. Eloussifi, B. Villarejo, P. Roura, J. Farjas, A. Calleja, A. Palau, X Obradors, T. Puig, S. Ricart, Supercond. Sci. Technol. 29 (2016) 024002. [10] W. Wu, F. Feng, Y. Zhao, X. Tang, Y. Xue, K. Shi, R. Huang, T. Qu, X. Wang, Z. Han, J.C. Grivel, Supercond. Sci. Technol. 27 (2014) 055006. [11] W. Bian, Y. Chen, W. Huang, G. Zhao, J. Nishii, H. Kaiju, M. Fujioka, L. Li, N. Li, F. Yan, Ceramics International 43 (2017) 8433-8439. [12] R. Feenstra, F.A. List, X. Li, M.W. Rupich, D.J. Miller, V.A. Maroni, Y. Zhang, J.R. Thompson, D.K. Christen, IEEE Trans. Appl. Supercond. 19 (2009) 3131-3135. [13] A. Llordés, K. Zalamova, S. Ricart, A. Palau, A. Pomar, T. Puig, A. Hardy, M.K. Van Bael, X. Obradors, Chem. Mater. 22 (2010) 1686-1694. [14] A.A. Armenio, A. Augieri, L. Ciontea, G. Contini, I. Davoli, M.D. Giovannantonio, V. Galluzzi, A. Mancini, A. Rufoloni, T. Petrisor, A. Vannozzi, G. Celentano, Supercond. Sci. Technol. 24 (2011) 115008. [15] Y. Zhao, J. Chu, T. Qureishy, W. Wu, Z. Zhang, P. Mikheenko, T.H. Johansen, J.C. Grivel, Acta Materialia 144 (2018) 844-852.
Figure Captions Fig. 1 AFM images of pyrolyzed films. (a) YBCO-FF (b) YBCO-LF/YBCO-FF. (c) The corresponding roughness of pyrolyzed films. Inset figure is optical microscopy of YBCO-LF/YBCO-FF. (d) θ-2θ scans of YBCO-LF/YBCO-FF pyrolyzed film, YBCO-LF and YBCO-FF as the reference samples. Fig.
2
Cross-SEM
images
of
pyrolyzed
films.
(a)
YBCO-FF,
(b)
YBCO-LF/YBCO-FF. Fig. 3 XPS of (a) Y3d, (b) Ba3d, (c) Cu2p, (d) O1s, (e) F1s, and (f) depth profile of YBCO-LF/YBCO-FF/LAO precursor film. Fig. 4 (a) θ-2θ scans of YBCO-LF/ YBCO-FF/LAO crystallized film. (b) Omega scan of YBCO (005) peak, (c) Phi scan of YBCO (103) peak, (d) Jc vs magnetic field 0H for YBCO-LF/ YBCO-FF crystallized film.
Fig. 1
Fig. 3
Fig. 2
Fig. 4
Highlights
YBCO Low-F/ YBCO F-Free composites have been fabricated by solution deposition method.
The effective F diffusion may tune the F and C residues of YBCO film.
This novel and simple process can improve the texture and Jc of YBCO film.
S0167-577X(19)30673-1 https://doi.org/10.1016/j.matlet.2019.04.108 MLBLUE 26091
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
24 February 2019 23 April 2019 26 April 2019
Please cite this article as: L.H. Jin, Y. Bai, C.S. Li, J.Q. Feng, L. Lei, G.Y. Zhao, L. Gao, P.X. Zhang, Growth of YBCO film by chemical solution deposition with an optimization fluorine process, Materials Letters (2019), doi: https://doi.org/10.1016/j.matlet.2019.04.108
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Growth of YBCO film by chemical solution deposition with an optimization fluorine process L.H. Jina,*, Y. Baib, C.S. Lia, J.Q. Fenga, L. Leib, G.Y. Zhaob, L. Gaoc, P.X. Zhanga a
Northwest Institute for Nonferrous Metal Research, Xi’an, 710016, China
b
Xi’an University of Technology, Xi’an, 710048, China
c
Xi’an Technological University, Xi’an, 710021, China
Abstract: Trifluoroacetate metal organic deposition (TFA-MOD) with low fluorine contents would bring benefits for the environment and the epitaxial growth of YBa2Cu3Oy (YBCO) film. In this paper, a simple and effective method which could tune the fluorine content and improve the performance of YBCO film was reported. YBCO Low-Fluorine / YBCO Fluorine-Free composites were prepared on LaAlO3 single crystal substrate. During the pyrolysis process, the fluorine would diffuse across the interface of YBCO Low-Fluorine / YBCO Fluorine-Free composites. Both the fluorine in the YBCO Low-Fluorine and the carbon in the YBCO Fluorine-Free could be reduced. It could significantly improve the epitaxial growth and performance of YBCO film. Keywords: YBCO film; MOD; Fluorine * Corresponding author. Email: [email protected].
1. Introduction Chemical solution deposition (CSD) has been successfully employed to prepare YBaCu3Oy (YBCO) coated conductor with high performance. According to the presence of fluorine, CSD routes include trifluoacetate metal organic deposition (TFA-MOD) [1], and fluorine-free (FF) solution route [2]. TFA-MOD shows low cost merits for the scale production [3]. During the heat treatment, the significance
intermediate phase is the formation of BaF2 instead of BaCO3, because the stable BaCO3 can make the weak-link behavior and decrease the critical current density of final YBCO film. However, the conventional TFA-MOD method needs a slow decomposition process which is not suitable for the fabrication of long length coated conductors. The control of fluorine content may offer the possibility of fast pyrolysis process, minor harmful fluorine byproducts, higher grain growth rate and good performance of REBCO film [4]. Hence, the special heat treatment process and the modified precursor solution are developed to tune the fluorine content. The fluorine (F)-free precursors were used as alternatives to prepare low fluorine solutions. The F-free copper naphthenate or copper octylate were also employed as precursors in advanced TFA-MOD process by SRL-ISTEC [5,6]. In our previous work, we have replaced copper trifluoroacetate by copper benzoate or acetate to fabricate homogeneous film in fast pyrolysis process [7,8]. Palmer et al designed low fluorine solutions using different quantities of fluorine and non-fluorine carboxylate precursors with a total amount of fluorine from 10% to 50% [9]. Wu et al synthesized an ultralow fluorine solution to fabricate YBCO film with high performance [10]. And the effect of F/Ba ratio on the properties of the YBCO films was systematically investigated by Bian et al [11]. Furthermore, a large F concentration may produce uncontrollable amounts of BaOF liquid in the thick film. Feenstra et al introduced a medium-temperature anneal process (F-module) between pyrolysis and crystallization to decrease the F concentrations [12]. In this paper, a new method was developed to tune the fluorine content for YBCO film growth. The YBCO Low-F/ YBCO F-free films were prepared from the low fluorine solution (F%=23.1%) and fluorine-free solution (F%=0). The fluorine diffusion from YBCO Low-F layer to YBCO F-free layer is considered to tune the
fluorine and carbon residues. It improves the texture and performance of YBCO film. 2. Experimental For the low-fluorine precursor solution (YBCO-LF, F content = 23.1%) [8], the precursors included yttrium trifluoroacetate (Y(CF3COO)3), barium propionate (Ba(C2H5COO)2) and copper propionate (Cu(C2H5COO)2). In contrast, yttrium acetate (Y(CH3COO)3), Ba(C2H5COO)2 and Cu(C2H5COO)2 were used to prepare the fluorine-free solution (YBCO-FF, F%=0%). All mixtures were dissolved separately in methanol and propionic acid (CH3OH:C2H5COOH = 1:1). The stoichiometry of metallic cations was a fixed value (Y:Ba:Cu = 1:1.5:3). The solutions were heated to 80 oC for 30 min with continuous stirring to obtain stable blue-colored solutions with a total cations concentration of 1.2 mol/L. The LaAlO3 single crystal (LAO, 10 mm × 10 mm) substrate was cleaned in the ultrasonic acetone bath for 20 min. Firstly, the fluorine-free solution was firstly deposited on LAO substrates by spin coating with a spinning rate of 2000 rpm for 2 min. The gel film was pyrolyzed at 450 oC under humidified oxygen atmosphere to form the YBCO-FF/LAO pyrolyzed film. Secondly, the low fluorine solution was coated and pyrolyzed to form YBCO-LF/YBCO-FF/LAO pyroyzed films. Thirdly, the YBCO-LF/YBCO-FF/LAO precursor films were crystallized at 800 oC for 2h in Ar-0.01%O2 atmosphere with 4.2% humidity. Finally, the crystallized films were annealed at 450
o
C for 4 h in a dry oxygen atmosphere to form YBCO
superconducting film with orthorhombic phase. The morphology of YBCO films were characterized by scanning electron microscopy (SEM S-4800), optical microscopy (OM Olympus PMG3) and atomic force microscopy (AFM SPM-9500J3). The chemical states of film were evaluated by X-ray photoelectron spectra analysis (XPS, ESCALAB 250Xi). The phase
composition of film was investigated by X-ray diffraction using CuKα radiations (XRD Bruker D8 Advance). The critical current density (Jc) was determined by VSM (VersaLab, Quantum Design). 3. Results and discussion YBCO precursor films derived from the fluorine-free solution and low fluorine solution were pyrolyzed at 450 oC using the heating rate of 5 K/min to form YBCO-LF/YBCO-FF/LAO. Fig. 1 shows the surface morphologies and x-ray diffraction
patterns
pyrolyzed
films.
The
surface
of
YBCO-FF
and
YBCO-LF/YBCO-FF pyrolyzed films are smooth and homogeneous without carks or wrinkles. It implies that the decomposition stress can be gently released under the relatively
high
ramping
speed.
However,
the
surface
morphology
of
YBCO-LF/YBCO-FF is flatter than that of YBCO-FF. The roughness (Rrms) value of YBCO-LF/YBCO-FF is ~1.84 nm in the scanning area of 5 µm × 5 µm, which is smaller
than
that
of
YBCO-FF
(Rrms =
~5.06nm).
The
roughness
of
YBCO-LF/YBCO-FF is close to that of YBCO-LF precursor film in scanning areas of 5µm × 5µm and 10µm × 10µm (Fig. 1c). The presence of fluorine may promote the uniform decomposition reaction and be beneficial for the acquirement of smooth surface. Fig. 1d gives the corresponding θ-2θ XRD patterns. The peaks of CuO and BaF2 can be observed in YBCO-LF/YBCO-FF pyrolyzed film. Moreover, Ba1-xYxF2+x (BaYF) and CuO phases can be observed in YBCO-LF. The very weak peak ascribed to monoclinic BaCO3 phase can be detected in YBCO-FF. In comparison with the YBCO-LF, there is the unusual formation of BaF2 in the YBCO-LF/YBCO-FF. Y3+ ions may release from BYF phase to form Y-O-F or Y2O3 phase [8]. It indicates that there is fluorine diffusion between the top coating and bottom coating. The formation of BaF2 phase in YBCO-LF/YBCO-FF may be suitable for the ex-situ “BaF2 process”
and useful for the growth of YBCO film. The cross-SEM morphology of YBCO-FF and YBCO-LF/YBCO-FF pyrolyzed films are shown in Fig. 2. The clear interface between substrate and pyrolyzed film can be observed in the samples. The thickness of YBCO-LF/YBCO-FF reaches at ~600nm. The thicknesses of top and bottom coatings are ~340nm and ~260nm, respectively. There is no vertical open porosity in YBCO-LF/YBCO-FF. The composite is less porous than all TFA-YBCO film pyrolyzed under oxygen atmosphere [13]. The composite may be useful for a release of pyrolysis subproducts and a dense precursor film. Fig. 3 shows the XPS of Y3d, Ba3d, Cu2p, O1s, F1s, and depth profile of YBCO-LF/YBCO-FF/LAO precursor film. Y 3d5/2 spectrum shows the split double peaks located at binding energies of ~158.9eV and ~156.7eV (Fig.3a) [14]. It can be ascribed to the presence of Y2O3 and YF3. And there is only minor YF3 phase in the film according to the weak binding energy peak. It can form Y-O-F clusters and is consistent with the XRD analysis of film. Two peaks of Ba 3d3/2 and Ba 3d5/2 energy levels are at binding energies of ~795.4 and ~780.2 eV, as shown in Fig.3b. It represents binding energy of BaF2. Cu spectrum shows two peaks at binding energies of ~932.6 eV and ~952.4 eV (Fig.3c). The peaks are consistent with Cu 2p3/2 and Cu 2p1/2 and the presence of CuO or Cu2O. The spectrum of O 1s presents the maximum peak at ~529 eV with a shoulder peak at ~531.1eV (Fig. 3d). It can be assigned to the binding energies of Y-O and Cu-O compounds. A sharp and intense F 1s peak at binding energy of ~684.2eV can be observed in Fig. 3e. It is consistent with the presence of BaF2 and Y-O-F. F 1s in BaF2, YF3 and CuF2 are typically located at the binding energies of ~683.7 eV, ~685.3 eV and ~685.9 eV, respectively. Hence, the BaF2, Y-O-F and CuO or Cu2O are main phases in the film. The variation of Ba, F, C
elements after Ar+ bombardment are shown in Fig. 3f. F element can be detected in the whole XPS depth profile of YBCO-LF/YBCO-FF. The F content decreases firstly and then increases from YBCO-LF to YBCO-FF. Furthermore, the carbon content can be obviously reduced when fluorine enters into YBCO-FF. It clearly indicates that the fluorine diffuse from the YBCO-LF to the YBCO-FF. Fig. 4 shows the typical θ-2θ scan, scan, ω scan and Jc-B curve of crystallized films. The strong YBCO (00l) peaks without other peaks can be observed in Fig. 4a. It indicates there are only high c-axis preferred orientation grains in the YBCO-LF/YBCO-FF crystallized film. The omega scan of YBCO (005) peak and phi scan of YBCO (103) peak are shown in Fig. 4b and 4c. The full-width at half maximum (FWHM) value of out-of-plane (∆ω) is ~0.9o. The in-plane scan consists of four peaks with the average FWHM value (∆) of ~1.47o. The FWHM value of in-plane scan is comparable to that of YBCO film (∆1.3 o) prepared by the solution with 20% F content [9]. In addition, the FWHM values of ∆ω and ∆are close to the results of LF-YBCO film (∆ω =0.8o and ∆o) [2,15]. It indicates good in-plane and out-of-plane alignments of YBCO-LF/YBCO-FF crystallized film. The dependence of Jc on magnetic field is shown in Fig. 4d. The whole thickness of crystallized film is at ~360nm and the Jc value of YBCO-LF/YBCO-FF reaches at ~3.98 MA/cm2 at 77K, 0T. The Jc decreases rapidly with increasing the applied magnetic field. In the references [2,10,15], the Jc values of 3~5MA/cm2 (77K, 0T) could be achieved in the ~200nm thick LF-YBCO films. And the Jc values decreased obviously to ~2MA/cm2 on the ~450nm thick film. However, in this work, the high performance can be maintained in the thick YBCO-LF/YBCO-FF film. Therefore, this double layer structure may be beneficial for the acquirement of good texture and high performance.
4. Conclusions YBCO Low-Fluorine / YBCO Fluorine-Free composites have been fabricated on LAO substrate by solution deposition method. The simple and effective method is used to smooth the surface, tune the fluorine content and improve the microstructure. The fluorine can diffuse from YBCO-LF to YBCO-FF and reduce the carbon content of YBCO-FF. It contributes to the acquirement of high c-axis preferred orientation grains and sharp texture. The FWHM values of omega and phi scans are ~0.9o and 1.47o, respectively. And the YBCO-LF/YBCO-FF crystallized film shows high Jc of ~3.98 MA/cm2. This method may be beneficial for good texture and high performance of YBCO crystallized film. Acknowledgements This work was financially supported by the National Science Fund Program of China (No.51777172), the Natural Science Basic Research Plan in Shaanxi Province (No. 2017ZDJC-19). References [1] T. Izumi, K. Nakaoka, Supercond. Sci. Technol. 31 (2018) 034008. [2] Y. Zhao, P. Torres, X. Tang, P. Norby, J.C. Grivel, Inorg. Chem. 54 (2015)
10232-10238. [3] M.W. Rupich, D.T. Verebelyi, W. Zhang, T. Kodenkandath, X. Li, Mater. Res. Soc. Bull. 29 (2004) 572-578. [4] P. Cayado, B. Mundet, H. Eloussifi, F. Vallés, M. Coll, S. Ricart, J. Gázquez, A. Palau, P. Roura, J. Farjas, T. Puig, X. Obradors, Supercond. Sci. Technol. 30 (2017) 125010. [5] Y. Tokunaga, T. Honjo, T. Izumi, Y. Shiohara, Y. Iijima, T. Saitoh, T. Goto, A. Yoshinaka, A. Yajima, Cryogenics 44 (2004) 817-822. [6] H. Ichikawa, K. Nakaoka, M. Miura, Y. Sutoh, T. Nakanishi, A. Nakai, M. Yoshizumi, T. Izumi, Y. Shiohara, Physica C 469 (2009) 1329-1331. [7] L.H. Jin, Y.F. Lu, J.Q. Feng, S.N. Zhang, Z.M. Yu, Y. Wang, C.S. Li, J. Alloy. Compd. 568 (2013) 36-41.
[8] L.H. Jin, C.S. Li, J.Q. Feng, Z.M. Yu, Y. Wang, L. Lei, G.Y. Zhao, A. Sulpice, P.X. Zhang, Supercond. Sci. Technol. 29 (2016) 015001. [9] X. Palmer, C. Pop, H. Eloussifi, B. Villarejo, P. Roura, J. Farjas, A. Calleja, A. Palau, X Obradors, T. Puig, S. Ricart, Supercond. Sci. Technol. 29 (2016) 024002. [10] W. Wu, F. Feng, Y. Zhao, X. Tang, Y. Xue, K. Shi, R. Huang, T. Qu, X. Wang, Z. Han, J.C. Grivel, Supercond. Sci. Technol. 27 (2014) 055006. [11] W. Bian, Y. Chen, W. Huang, G. Zhao, J. Nishii, H. Kaiju, M. Fujioka, L. Li, N. Li, F. Yan, Ceramics International 43 (2017) 8433-8439. [12] R. Feenstra, F.A. List, X. Li, M.W. Rupich, D.J. Miller, V.A. Maroni, Y. Zhang, J.R. Thompson, D.K. Christen, IEEE Trans. Appl. Supercond. 19 (2009) 3131-3135. [13] A. Llordés, K. Zalamova, S. Ricart, A. Palau, A. Pomar, T. Puig, A. Hardy, M.K. Van Bael, X. Obradors, Chem. Mater. 22 (2010) 1686-1694. [14] A.A. Armenio, A. Augieri, L. Ciontea, G. Contini, I. Davoli, M.D. Giovannantonio, V. Galluzzi, A. Mancini, A. Rufoloni, T. Petrisor, A. Vannozzi, G. Celentano, Supercond. Sci. Technol. 24 (2011) 115008. [15] Y. Zhao, J. Chu, T. Qureishy, W. Wu, Z. Zhang, P. Mikheenko, T.H. Johansen, J.C. Grivel, Acta Materialia 144 (2018) 844-852.
Figure Captions Fig. 1 AFM images of pyrolyzed films. (a) YBCO-FF (b) YBCO-LF/YBCO-FF. (c) The corresponding roughness of pyrolyzed films. Inset figure is optical microscopy of YBCO-LF/YBCO-FF. (d) θ-2θ scans of YBCO-LF/YBCO-FF pyrolyzed film, YBCO-LF and YBCO-FF as the reference samples. Fig.
2
Cross-SEM
images
of
pyrolyzed
films.
(a)
YBCO-FF,
(b)
YBCO-LF/YBCO-FF. Fig. 3 XPS of (a) Y3d, (b) Ba3d, (c) Cu2p, (d) O1s, (e) F1s, and (f) depth profile of YBCO-LF/YBCO-FF/LAO precursor film. Fig. 4 (a) θ-2θ scans of YBCO-LF/ YBCO-FF/LAO crystallized film. (b) Omega scan of YBCO (005) peak, (c) Phi scan of YBCO (103) peak, (d) Jc vs magnetic field 0H for YBCO-LF/ YBCO-FF crystallized film.
Fig. 1
Fig. 3
Fig. 2
Fig. 4
Highlights
YBCO Low-F/ YBCO F-Free composites have been fabricated by solution deposition method.
The effective F diffusion may tune the F and C residues of YBCO film.
This novel and simple process can improve the texture and Jc of YBCO film.