Effect of an organic dye on the ferroelectric phase transition in KH2PO4 (KDP)

This paper reports on the first measurement of the dielectric permittivity and heat capacity of a KDP crystal doped by Chicago Sky Blue organic dye within a temperature interval including the ferroelectric phase transition at T _c =122 K. Similar measurements were made on a pure KDP crystal under the same conditions for the sake of comparison. The heat capacities of the pure and doped crystals were shown to differ substantially within an interval 1 K wide in the vicinity of T _c , where an anomaly in the heat capacity of the doped crystal was observed to wash out without producing any change in the temperature position of its maximum. The doping reduces the permittivity in the polar phase markedly. The observed effects are associated with the influence of nonisomorphic defects on the ferroelectric phase transition in a piezoelectric crystal.