  Effects of columnar defects created by 320 MeV Au irradiation on 2H-NbSe2
single crystals with a dose equivalent matching field up to 16 T were studied.
Critical temperature is found to be suppressed almost linearly at a rate of
0.07 K/T. At the same time, the lattice parameters a and c are found to be
expanded at rates of 0.016%/T and 0.030%/T, respectively. Such a lattice
expansion should work as negative pressure to affect Tc. By separating the
effect of heavy-ion irradiation on Tc suppression through lattice expansion and
disorder, it is found that Tc is suppressed more by lattice expansion rather
than by disorder.
