ANOMALOUS CHANGE IN TEMPERATURE DURING THE PRESSURE-INDUCED PHASE-TRANSITION OF KI

Temperature changes associated with the pressure-induced phase transition of KI were observed. Two kinds of temperature signals were detected, one of which is endothermic due to the adiabatic expansion of the pressure transmitting liquid brought about by the discontinuous decrease in the sample volume. The other is an exothermic one transmitted from the sample by radiation, which means heating of a sample at the forward transition. The latter signal consists of a spike accompanied by a small but long-tailed signal. The heating at the forward transition is inconsistent with the negative slope of the phase boundary in the accepted pressure-temperature phase diagram. Although the pattern of temperature signals observed seems to support the transition mechanism of the nucleation of B2 and its growth, this mechanism contradicts the behavior of the fracture plane of KI which suggests some kind of Martesite transformation. In a reverse transition, complicated temperature signals were detected.