METASTABLE REGIONS IN THE P-T DIAGRAM OF KNO3 CLOSE TO THE TRIPLE POINT

The pressure - temperature diagrams of order - disorder ferroelectrics such as KNO3 often contain two triple points, (p(ki),T-ki)= (0.12kbar , 401K) and (3.0kbar, 294K) for KNO3. A more detailed inspection of th e transition lines reveals that all transitions are of first order and that several metastable regions penetrate each other close to (p(k1), T-k1) Isobaric DTA - experiments show unexpected heat anomalies inside of the combined metastable region. This and the rare occurence of a c losed region for the low temperature phase is discussed on the basis o f the Landau theory.