Magnetoresistance measurements have been carried out along the highly
conducting a axis in the FISDW phase of hydrogened and deuterated
(TMTSF)2​ClO4​ for various cooling rates through the anion ordering
temperature. With increasing the cooling rate, a) the high field phase boundary
βHI​, observed at 27 T in hydrogened samples for slowly cooled,
is shifted towards a lower field, b) the last semimetallic SDW phase below
βHI​ is suppressed, and c) the FISDW insulating phase above
βHI​ is enhanced in both salts. The cooling rate dependence of
the FISDW transition and of βHI​ in both salts can be explained
by taking into account the peculiar SDW nesting vector stabilized by the
dimerized gap due to anion ordering.Comment: 6pages,6figures(EPS), accepted for publication in PR