Raman spectrum of the puzzling paraelectric phase of nickel-iodine boracite

Abstract
The Raman spectrum of Ni3B7O13I is reported and the number of q=0 phonon frequencies observed is compared with the group-theoretical prediction. Anomalies in the temperature dependence of phonon lifetimes and frequencies are correlated with abnormalities in the dielectric, magnetic and structural properties at approximately=130K. The Raman spectra at temperatures from 88K to 300K indicate cubic symmetry. The static and temperature dependent structure of the Raman spectra are compared and contrasted with their counterparts for other boracites. It is concluded that Ni3B7O13I is unique among boracites in many ways, at least in its cubic phase.

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