ANALYSIS OF THE FREQUENCY SHIFTS CLOSE TO THE SECOND ORDER PHASE TRANSITION IN NH₄Cl

Abstract

In this study we analyzed observed Raman data for the frequencies of the disorder-induced modes of ν₇ (93 cm⁻¹) and ν₅ (144 cm⁻¹) in the second order phase region of NH₄Cl (P = 2.8 kbar). By means of a power-law formula describing the critical behaviour of the frequency shifts for those phonon modes studied, we extract the critical exponent value of a = 0.25, which can also describe the critical behaviour of the specific heat C _p close to the second order phase transition in NH₄Cl. Within this content, our spectroscopically modified Pippard relations are introduced here.

Keywords:

• Raman
• Phase transition
• NH₄Cl
• Disorder-induced modes
• Ammonium halides
• Phase transitions

Acknowledgments