Raman studies on ferroelectric phase (phase III) of KNO3

In order to understand the nature, stability, and existence temperature wid th of phase I, phase II, and phase III (ferroelectric phase) of KNO3, a det ailed Raman investigation was carried out with various heating/cooling rate s, repeated thermal cycles, and different preheating temperatures. The incr ease in the existence temperature width of the phase III of KNO3 was observ ed with the increase of heating/cooling rate but the repeated thermal cycli ng 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 high er preheating temperature. The phase III could be retained down to room tem perature with higher cooling rate and higher preheating temperature. This c ould be important in its applications. The coexistence of phase III with ph ase II was observed with all the heating/cooling rates. In this work, speci al attention was also paid to study the behavior of the lattice modes of KN O3 during the successive phase transformations. (C) 1999 American Institute of Physics. [S0021-8979(99)05524-3].