  Thermal conductivity measurements in magnetic fields have been carried out
for FeSe$_{0.3}$Te$_{0.7}$ single crystals as-grown and annealed at 400
{\degree}C for 100 h in vacuum ($\sim$ 10$^{-4}$ Pa). It has been found that
the thermal conductivity in the {\it ab}-plane, {\kab}, of the annealed crystal
shows an enhancement at low temperatures just below the superconducting
transition temperature, {\tc}, owing to the thermal conductivity due to
quasiparticles, while {\kab} of the as-grown crystal does not. This suggests
that FeSe$_{1-x}$Te$_{x}$ is a strongly correlated electron system. It has also
been found that both the degree of the enhancement of {\kab} just below {\tc}
and the behavior of the suppression of {\kab} by the application of magnetic
field for the annealed crystal depend on the thickness of the crystal. These
results indicate that bulk superconductivity is absent in the as-grown crystal,
appears only in the surface area in the annealed-thick crystal and appears in
the almost whole region in the annealed-thin crystal. It has been concluded
that the excess Fe included in the as-grown crystal is removed from the surface
through the vacuum-annealing.
