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 *NO-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. © 1979.