FIRST-ORDER TRANSITIONS BY CONDUCTION CALORIMETRY - APPLICATION TO DEUTERATED POTASSIUM DIHYDROGEN PHOSPHATE FERROELASTIC CRYSTAL UNDER UNIAXIAL PRESSURE

The specific heat c and the heat power W exchanged by a Deuterated Pot assium Dihydrogen Phosphate ferroelectric-ferroelastic crystal have be en measured simultaneously for both decreasing and increasing temperat ure at a low constant rate (0.06 K/h) between 175 and 240 K. The measu rements were carried out under controlled uniaxial stresses of 0.3 and 4.5+/-0.1 bar applied to face (110). At T-t = 207.9 K, a first order transition is produced with anomalous specific heat behavior in the in terval where the transition heat appears. This anomalous behavior is e xplained in terms of the temperature variation of the heat power durin g the transition. During cooling, the transition occurs with coexisten ce of phases, while during heating it seems that metastable states are reached. Excluding data affected by the transition heat, the specific heat behavior agrees with the predictions of a 2-4-6 Landau potential in the range of 4-15 K below T-t while logarithmic behavior is obtain ed in the range from T-t to 1 K below T-t. Data obtained under 0.3 and 4.5 bar uniaxial stresses exhibit the same behavior. (C) 1997 America n Institute of Physics.