  We have investigated experimentally how properties of NdFeAsO0.8F0.2
superconductor affected due to the substitution of the calcium by the
neodymium. We have synthesized polycrystalline Nd1-xCaxFeAsO0.8F0.2 samples
with x=0, 0.01, 0.025, 0.05 and 0.1 through the one step solid state reaction
method. The X-ray diffraction patterns, refined using the MAUD software and
Rietveld s method, have indicated the formation of tetragonal structure with
the space group P4/nmm:2. We studied various structural parameters such as
lattice parameters, bond angles, bond length, and etc. Based on the XRD data
refinement, we have determined the upper limit of the calcium solubility in
Nd-1111 structure and it is restricted to x 0.05. Also, we found that the
lattice parameter a was almost constant by increasing the calcium content,
while the lattice parameter c and the cell volume decreased. Based on XRD data
analysis, we have inference that these are due to the variations in the bond
angles of As-Fe-As {\alpha} and \b{eta} and a decrease in the bond lengths upon
increasing x. So, we have expected that the superconducting transition
temperature will be sensitive to the calcium doping. Experimentally, the
superconducting transition temperature was reduced from 55K (x = 0) to 48K (x =
0.01) and disappeared for other samples. On the other hand, it can be concluded
from our study results about of the structural and electrical properties, which
the superconducting transition temperature decreased with increasing the
distortion of FeAs4-tetrahedrons from regular one. Also, based on
Williamson-Hall equation, the microstrain of the samples increased upon
increasing x and for Nd0.95Ca0.05FeAsO0.8F0.2 sample was grown approximately
three times in comparison to the pure sample. So, it is noticeable that there
is a relation between the structural properties and superconductivity in our
samples.
