The temperature and frequency dependent dielectric relaxation data and simultaneous observation of optical texture reveal co-existence of ferroelectric (SrnC*) and antiferroelectric (SmCA*) phases in the pre-transition regime of the anti ferroelectric liquid crystal (AFLC) sample viz. (R)-4-[1-methyl-2-(2,2,3,3,3-pentafluoropropyloxy)ethyloxy)carbonyl]phenyl 4'-decyloxybiphenyl-4-caboxylate. Interestingly, this sample shows irreversible change in the antiferroelectric to ferroelectric (AFE -> FE) phase transition temperature (TO) for consecutively increasing bias field treatment in successive cycles. The lowest upper bound of the threshold field for AFE -> FE transition at the boundary of the said phases is found to be similar to 1 kV cm(-1). (C) 2008 Elsevier B.V. All rights reserved.