Enhancement of Zero Resistance Temperature above 90 K and Hole Distribution in (Hg(0.5)Pb(0.5))Sr(2)(Ca(0.7)Y(0.3))Cu(2)O(7-delta) via Chemical Substitution of Ba into Sr Sites.
A significant enhancement of zero resistance temperature [T(c(zero))] from 78 K for x = 0 to 92.5 K for x = 0.2 in the series (Hg(0.5)Pb(0.5))(Sr(2-x)Ba(x))(Ca(0.7)Y(0.3))Cu(2)O(7-delta) compounds has been found. On the basis of the O K-edge X-ray-absorption near-edge structure (XANES) spectra for the series of (Hg(0.5)Pb(0.5))(Sr(2-x)Ba(x))(Ca(0.7)Y(0.3))Cu(2)O(7-delta) samples with x = 0-0.5, the chemical substitution of Ba(2+) for Sr(2+) gives rise to a decrease in the O 2p hole concentration within the out-of-plane oxygen sites, while that within the in-plane CuO(2) layers remains almost unchanged for 0 </= x </= 0.2. This indicates that the out-of-plane oxygen may play an important role in controlling the increase of T(c(zero)) up to the maximum value of 92.5 K.
Liu
R. S.
RS
Department of Chemistry, National Taiwan University, Taipei, Taiwan, ROC, Synchrotron Radiation Research Center, Hsinchu, Taiwan, ROC, and Materials Research Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan, ROC.
Chen
J. M.
JM
Shy
D. S.
DS