Bd. Padalia et al., LOCAL STRUCTURE AROUND CATIONS IN THE T'-TYPE ND(CE) BASED SUPERCONDUCTING SYSTEM - AN EXAFS STUDY, Journal of physics. Condensed matter, 9(44), 1997, pp. 9695-9714
EXAFS measurements on all the cations in Nd2CuO4, Nd2-xCexCuOy (NCCO)
and Nd(1.82-z)A(z)Ce(0.18)CuO(y) (NACCO), A=Sr, Ca or Ba, x = 0.06 or
0.18, have been made using synchrotron radiation. Bond lengths (R), co
ordination numbers (N) and Debye-Waller factors (sigma(2)) have been o
btained from the EXAFS analysis. The curved wave theory in the single-
scattering approximation and the small-atom multiple-scattering theory
have been applied to experimental EXAFS data and it is found that the
latter gives a better fit. The CuO2 plane contains a strong multiple-
scattering contribution. Further, all the dopants (Ce, Sr, Ca and Ba)
occupy the Nd site without affecting the basic T' structure. Doping af
fects the local structure around the substituents as reflected by the
changes in R and sigma(2) values. The observed CuO2 layer distortion (
or large Cu-O-Cu angle deviation from linearity, 180 degrees) is found
to have an adverse effect an T-c as observed in Ca or Ba doped NACCO
samples. Further, it is realized that critical levels of charge carrie
rs, oxygen vacancies and CuO2 planar effects have a strong influence o
n the SC behaviour of the T'-type electron doped cuprates.