Raman studies on ferroelectric phase (phase III) of KNO3

In order to understand the nature, stability, and existence temperature width of phase I, phase II, and phase III (ferroelectric phase) of KNO3, a detailed Raman investigation was carried out with various heating/cooling rates, repeated thermal cycles, and different preheating temperatures. The increase in the existence temperature width of the phase III of KNO3 was observed with the increase of heating/cooling rate but the repeated thermal cycling reduced it. The phase III to phase II transformation extended to a lower temperature in the cooling process when the sample was subjected to a higher preheating temperature. The phase III could be retained down to room temperature with higher cooling rate and higher preheating temperature. This could be important in its applications. The coexistence of phase III with phase II was observed with all the heating/cooling rates. In this work, special attention was also paid to study the behavior of the lattice modes of KNO3 during the successive phase transformations. (C) 1999 American Institute of Physics. [S0021-8979(99)05524-3].