Chemical control of hole distribution and superconductivity in (Cu,Mo)Sr-2(Ce,R)(s)Cu2O5+2s+delta (s=2, 3; R = Y, La-Yb)
Journal
Chemistry of Materials
Journal Volume
18
Journal Issue
26
Pages
6352-6356
Date Issued
2006
Author(s)
Abstract
In the crystal structure of members of the (Cu,Mo)Sr2(Ce,R) sCu2O5+2s+δ or (Cu,Mo)-12s2 homologous series of superconductive copper oxides, adjacent CuO2 planes are separated by a fluorite-structured (Ce,R)-[O2-(Ce,R)]s-1 blocking block. Here we utilize the fluorite block as a "chemical-pressure medium" for the s = 2 and 3 members of the series. The (Ce,R) sites readily accommodate rare earth elements (R) ranging in size from La down to Yb. With decreasing size of the R constituent, Tc first monotonically increases and then decreases, having a maximum around R = Y for both s = 2 and s = 3. At the same time the average valence of copper, derived for the s = 2 samples from Cu L3-edge XANES spectra, is found to remain constant at 2.20 ±0.01. An explanation for the unique chemical-pressure effect is revealed from O K-edge XANES spectra, the resolution of which allows us to distinguish the CuO2 plane holes from those residing in the (Cu,Mo)O1+δ charge reservoir. The result shows that the T c value and the density of CuO2 plane holes follow parallel trends with respect to the size of R. © 2006 American Chemical Society.
Type
journal article