  The issue concerning the nature and the role of microstructural
inhomogeneities in iron chalcogenide superconducting crystals of FeTe0.65Se0.35
and their correlation with transport properties of this system was addressed.
Presented data demonstrate that chemical disorder originating from the kinetics
of the crystal growth process significantly influences the superconducting
properties of an Fe-Te-Se system. Transport measurements of the transition
temperature and critical current density performed for microscopic bridges
allow us to deduce the local properties of a superconductor with
microstructural inhomogeneities, and significant differences were noted. The
variances observed in the local properties were explained as a consequence of
weak superconducting links existing in the studied crystals. The results
confirm that inhomogeneous spatial distribution of ions and small hexagonal
symmetry nanoscale regions with nanoscale phase separation also seem to enhance
the superconductivity in this system with respect to the values of the critical
current density. Magnetic measurements confirm the conclusions drawn from the
transport measurements.
