Phase relationships and cation disorder in RE{sub 1+x}Ba{sub 2-x}Cu{sub 3}O{sub 7+{delta}}, RE = Pr, Nd, Sm, Gd Page: 4 of 6
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comparisons of structural parameters from various sources is suspect. However, these data indicate that lattice
parameters, hence superconductivity, can be tailored by altering LRE composition and PO2.
DISCUSSION
Earlier work showed that the phase relationships in the La, Pr and Nd-Ba-Cu-O systems are not identical, even for
those sub-solidus compositions around the LREI23ss [1-7]. Figure 5 shows the sub-solidus phase relationships
for Pr-Ba-Cu-O and Nd-Ba-Cu-O systems in air at 950 C. While both systems show considerable solubility for
the LRE on the Ba site in the LRE123ss, the equilibrium phase assemblages are very different. In particular, note
that the LRE2I I structure does not exist in either of these two systems. Since Prl23 is not superconducting,
various studies have used Pr doped RE123 to probe the nature of the charge transfer in these ceramics. Although
Pr readily substitutes for the other RE's, high doping levels of Pr could result in subtle, complex microstructures.
For instance, a nominal substitution of Pr for Ba in Ndl23ss results in a very different structure than nominal
substitution of Pr for Nd in Ndl23ss [13]. Thus, an understanding of these variations in the phase relationships
must be taken when doing experiments in the Pr doped LRE123 systems./.
INAIA
II.C. 1NJOI C
Fig. 5 Subuslidu phaw ealtionships in the Pr-Ba-Cu-O [7] and Nd-Ba-Cu-O [8] systems.
'Table I. Solid solubility limits for LRE in the Ba sites in LREI ,Ba2.,CutO7.
LRE" Ionic Lower Upper Temperature ("C) P02 (bar)
Radii Limit Limit
La' 1.061 0.02 0.70 977 1.0
0.02 0.70 0.01
Pr 1.013 0.01 na 880 0.2
0.03 0.7 1.0
0.01 0.7 0.01
Nd 0.995 0.04 0.60 890 0.2
0.03 ., 0.38 950 1.0
0,00 0.60 - 940 .001
Stm1. 0.964 0.00 0.70 1025 1.0
0.00 0.15 950 0.01
1:11' 0.950 0.0 0.25 950 1.0
0.0 0.1 940 0.01
Gd" 0.938 0.0 0.20 950 1.0
0.0 0.04 950 0.01
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Kramer, M. J.; Wu, H.; Dennis, K. W.; Polzin, B. I.; Falzgraf, D. K. & McCallum, R. W. Phase relationships and cation disorder in RE{sub 1+x}Ba{sub 2-x}Cu{sub 3}O{sub 7+{delta}}, RE = Pr, Nd, Sm, Gd, article, December 31, 1995; Iowa. (https://digital.library.unt.edu/ark:/67531/metadc664517/m1/4/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.