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Nano-engineered defect structures in Ce- and Ho-doped metal-organic chemical vapor deposited YBa2Cu3O6+δ films: Correlation of structure and chemistry with flux pinning performance
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10.1063/1.3592244
/content/aip/journal/jap/109/11/10.1063/1.3592244
http://aip.metastore.ingenta.com/content/aip/journal/jap/109/11/10.1063/1.3592244

Figures

Image of FIG. 1.
FIG. 1.

(Color online) Dependence of J c on orientation angle of the field relative to the c-axis direction (maximum Lorentz force configuration) for films modified with various concentrations of (a) Ce and (b) Ho that display a substantial increase in J c for fields aligned near ab-planes relative to undoped YBCO films.

Image of FIG. 2.
FIG. 2.

(Color online) Cross-sectional TEM images of optimally doped YBCO films containing (a) 5 mol. % Ce, (b) 10 mol. % Ho, and (c) 20 mol. % Ho that illustrate the presence of high density precipitates mostly organized along the ab-planes.

Image of FIG. 3.
FIG. 3.

(a) Cross-sectional high-resolution TEM and (b) low-frequency filtered images of the same sample as presented in Fig. 2(a), showing a (Y,Ce)2O3 nanoplate defect, along with some of the stacking faults (white arrows) and antiphase boundaries (black arrows) associated with the platelet. The disruption and bending of the lattice fringes, which are evident from image (b), clearly indicate the presence of various defects within the YBCO matrix surrounding the platelike nanoprecipitates.

Image of FIG. 4.
FIG. 4.

(Color online) Images (a) through (d) show Y, Ce, Ba, and Cu spectral maps, respectively, taken over a representative domain of the 10 mol. % Ce-added YBCO film. (e) Displays the averaged EDS spectra obtained on the planar precipitates and YBCO matrix. The maps, along with the EDS spectra, reveal that the Ce is mainly incorporated in the nanoprecipitate arrays. The scale bar in inset (c) applies to all four maps.

Image of FIG. 5.
FIG. 5.

(Color online) Images (a) through (d) show Y, Ce, Ba, and Cu spectral maps, respectively, taken over a representative domain of the Ho-added YBCO film. (e) Shows the averaged EDS spectra obtained on the planar precipitates and YBCO matrix. The maps and the EDS spectra reveal that the added Ho incorporates into both the planar precipitates and the YBCO matrix.

Image of FIG. 6.
FIG. 6.

XRD patterns of YBCO films with (a) 5 mol. % Ce and (b) 5 mol. % Ho additions. Scans indicate formation of fluorite (RE2O3) phases along with c-axis growth of YBCO.

Image of FIG. 7.
FIG. 7.

(Color online) XRD determined fluorite phase fraction as a function of Ce and Ho doping levels. Dashed lines are intended to serve as a guide to the eye.

Image of FIG. 8.
FIG. 8.

(Color online) Normalized, averaged through-thickness Raman spectra of YBCO films doped with 2.5, 5, and 10 mol. % Ce. The typical Raman spectrum of an undoped MOCVD-YBCO film is also included for comparison. The bottom inset shows the results of subtraction of the undoped YBCO film spectrum from that of the 5 mol. % Ce-added film.

Image of FIG. 9.
FIG. 9.

(Color online) Comparison of the normalized, averaged through-thickness Raman spectra for the 2.5, 5, and 10 mol. % Ho-added samples together with the spectrum of an undoped MOCVD-YBCO film. Laser induced luminescence bands associated with Ho(III) in the fluorite phase lattice positions are highlighted with asterisks.

Image of FIG. 10.
FIG. 10.

(Color online) Comparison of the averaged through-thickness Raman spectra of the 20 mol. % Ho-added YBCO film and the Ho0.5Y0.5Ba2Cu3O6 + X film with the 633-nm-excited luminescence spectrum of Ho in the Ho2O3 standard.

Image of FIG. 11.
FIG. 11.

(Color online) Normalized Raman spectra of optimally doped Ce- and Ho-added MOCVD YBCO films (i.e., 5 mol. % Ce and 10 mol. % Ho). The results are displayed together with the spectrum of an optimally doped Zr-added MOCVD film (i.e., 5 mol. % Zr).

Image of FIG. 12.
FIG. 12.

(Color online) (a) Normalized x-ray absorption spectra in the Ho L3 edge region for the 2.5, 5, 10, and 20 mol. % Ho-added films and the Ho2O3 standard. The spectrum for the Ho0.5Y0.5Ba2Cu3O6 + X film is also included for comparison. (b) EXAFS Fourier transforms (radial coordinate plots) for the 10 mol. % Ho-added film, the Ho0.5Y0.5Ba2Cu3O6 + X film, and the Ho2O3 standard.

Image of FIG. 13.
FIG. 13.

(Color online) Comparison of the angular dependence of J c (77 K, 1 T) for YBCO films doped with “optimum” levels of Ce, Ho, and Zr. Angle-selective pinning enhancement is clearly evident for different additive elements.

Tables

Generic image for table
Table I.

Parameters for the volume fraction calculation.

Generic image for table
Table II.

Summary of superconducting properties for an undoped MOCVD YBCO film and for the Ce- and Ho-doped MOCVD YBCO films.

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/content/aip/journal/jap/109/11/10.1063/1.3592244
2011-06-15
2014-04-23
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Nano-engineered defect structures in Ce- and Ho-doped metal-organic chemical vapor deposited YBa2Cu3O6+δ films: Correlation of structure and chemistry with flux pinning performance
http://aip.metastore.ingenta.com/content/aip/journal/jap/109/11/10.1063/1.3592244
10.1063/1.3592244
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