ISSN:
1662-9752
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
We have performed neutron powder diffraction (NPD) experiments onpolycrystalline powders with nominal compositions (Ca〈sub〉0.5〈/sub〉La〈sub〉0.5〈/sub〉)(Ba〈sub〉1.25〈/sub〉La〈sub〉0.75〈/sub〉)Cu〈sub〉3〈/sub〉O〈sub〉7〈/sub〉- δ ,(Ca〈sub〉0.6〈/sub〉La〈sub〉0.4〈/sub〉)(Ba〈sub〉1.15〈/sub〉La〈sub〉0.85〈/sub〉)Cu〈sub〉3〈/sub〉O〈sub〉7〈/sub〉-δ and (Ca〈sub〉0.8〈/sub〉La〈sub〉0.2〈/sub〉)(Ba〈sub〉0.95〈/sub〉La〈sub〉1.05〈/sub〉)Cu〈sub〉3〈/sub〉O〈sub〉7〈/sub〉-δ . The diffraction patterns, analysed by the Rietveld method, show that all samples consist mainly of a tetragonal Y-123 type phase. Unit cell parameters a and c shorten as the calcium content increases: a = 3.8660(2), 3.8634(3), and 3.8624(5) Å; c = 11.6325(11), 11.6143(14), and 11.5822(20) Å for x-values 0.5, 0.6, and 0.8, respectively. For the x = 0.6 and 0.8 samples the Rietveld refinement of calcium occupancies and EDX analysis suggest that the actual composition is closer to x ≈ 0.5. However, since the lattice parameters do change, it is also suggested that at these higher doping levels calcium does enter the Y-site to a larger extent than for the x = 0.5 composition. This is also in accordance with previously reported values for the T〈sub〉c〈/sub〉, which decreases slighty as x changes from 0.5 to 0.6 and has a pronounced change from 80 K to 73 K for x = 0.6 and 0.8, respectively
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/02/07/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.443-444.361.pdf
Permalink