(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.
(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.
(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.
(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.
(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.
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.
(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.
(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.
(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.
(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.
(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).
(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.
(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.
Parameters for the volume fraction calculation.
Summary of superconducting properties for an undoped MOCVD YBCO film and for the Ce- and Ho-doped MOCVD YBCO films.
Article metrics loading...
Full text loading...