Impurity-induced first-order Raman spectra of KI and KBr in the fcc and sc phases

Abstract

The pressure dependences of the impurity-induced Raman spectra of KI and KBr have been measured for both fcc and sc structures, up to 30 kbar. Both materials have been observed to undergo phase transition at about 18 kbar. Four phonon bands have been observed for KI and three distinct peaks for KBr in the sc phase. From the measurement of the temperature dependence of the band intensities for KI between 300 and ∼80 K, these bands have been identified with first-order processes. The mode Grüneisen parameters for the two acoustic Eg modes in fcc phase and two acoustic and one optic mode in sc phase have been measured for both KI and KBr. The impurity-induced phonon bands of KI and KBr in both phases have also been correlated to the corresponding phonon branch singularity or singularities for most peaks.