Dynamical properties of crystals of Sr(NO3)2, Ba(NO3)2, and Pb(NO3)2. I. Infrared spectra and structure

Abstract
The far infrared reflection spectra of three single crystals of Sr(NO3)2, Ba(NO3)2, and Pb(NO3)2 are measured from 2500 to 10 cm−1 and from 10 to 300 K. The results are discussed on the basis of phonon and polariton theory. A method is found to determine the number of ordinary and extraordinary phonons in the case of general symmetry and a relation is established between the phonon frequencies and the polariton frequencies. These results are applied to discuss the spectra of Sr(NO3)2, Ba(NO3)2, and Pb(NO3)2. Then, among several structures proposed by different authors, the T4 structure is proposed from the results.

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