FAR INFRARED SPECTRA AND FERROELECTRIC PHASE TRANSITION OF $KNO_{3}$

Author Institution: General Motors Research LaboratoriesWhile it is known that in the ferroelectric phase of $KNO_{3}$ the nitrate ion is not located at the center of the potassium lattice, there is some uncertainty regarding the position of the nitrate ion in the high temperature paraelectric phase. Depending on whether or not it is centered on the potassium lattice, the paraelectric-ferroelectric phase transition should be either a displacive or an order-disorder type of transition. We found a strong band at $140 cm^{-1}$, and believe it to be produced by a phonon mode in which the potassium ions move against the nitrate ions. This mode was studied in both transmission and reflection as a function of temperature, with the reflection data being subjected to a classical oscillator analysis. The results of this analysis will be discussed in terms of the nature of the phase transition