Raman spectroscopic studies of temperature dependent anomalies of strontium,barium, lead,and calcium nitrate

Raman studies of normal and ¹⁸O-substituted Sr(NO₃)₂ have been performed over a range of temperatures (77 to 580°K) to investigate the anomalous component previously observed in the symmetric stretching region. The results suggest that the peak may have a hot band origin. Impurity ions, N ¹⁸O ¹⁶O^?₂ and vibrationally excited 1NO^?₃ ions, give rise to local modes (deep-well impurity centers) in the ν₁ and ν₄ (N ¹⁸O ¹⁶O^?₂ only) regions but delocalized modes (shallow-well impurity centers) in the other internal and external mode regions. The host lattice was able to tolerate a large fraction of this type of impurity without interference with the dynamical coupling. Anomalous properties previously reported appear to be due to freezing out of the hot band. A less complete study of Ca(NO₃)₂, Ba(NO₃)₂ at room temperature and at temperature near 500°K suggests behavior similar to Sr(NO₃)₂.