RAMAN FREQUENCIES CALCULATED FROM THE VOLUME DATA AS A FUNCTION OF TEMPERATURE AT HIGH PRESSURES FOR THE DISORDERED PHASE II OF NH4I

Abstract

In this study, we calculate the Raman frequencies as a function of temperature for the fixed pressures of 706, 1080 and 6355 bars using the volume data for phase II of ammonium iodide. The Raman frequencies calculated here are for the translational optic ν5 TO M (125 cm -1) lattice mode that is located at the zone boundary (M point) of the Brillouin zone of phase II for NH 4 I . For this calculation the volume data obtained at zero pressure, is used through the mode Grüneisen parameter for the disordered phase II (β phase) which has the CsCl structure of NH 4 I . Our predicted frequencies of the ν5 TO M (125 cm -1) mode can be compared when the Raman data for this lattice mode is available at various temperatures for fixed pressures of 706, 1080 and 6355 bars in the disordered phase II of ammonium iodide.