Raman scattering from NH4+ and ND4+ in beta-alumina

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Abstract
Polarized Raman spectra in the internal and external mode region of NH4+ and ND4+ ions in beta‐alumina have been measured. The forms of the scattering tensors for the internal modes are calculated taking into account the disordered distribution of ions on the crystallographic sites and treating each ion as an independent scattering center. The results of the analysis suggest that the ammonium ions occupy three nonequivalent sites in beta‐alumina. Model calculations indicate that the ions prefer the Beevers–Ross and midoxygen sites with the C2 axes of the ions located in the conducting plane. The librational modes of NH4+ and ND4+ evidently occur in the region from 200 to 450 cm−1, but overlap with phonons of the host lattice precludes positive identification. The in‐plane and out‐of‐plane translational modes are identified in the region between 100 and 200 cm−1.

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