Optical phonons in millerite (NiS) from single‐crystal polarized Raman spectroscopy

Although several fundamental physico‐chemical aspects of nickel sulfides have been studied in detail, particularly for millerite (nickel(II) monosulfide), the most common nickel sulfide mineral, no satisfactory investigation of optical vibrational modes has been reported previously. In this paper, we provide a definitive assignment of the optical phonons in millerite, investigated by polarized Raman spectroscopy on an oriented single crystal. The impact of the power of the incident laser beam on the spectra has also been investigated, revealing evidence for degradation in the quality of the spectra at sufficiently high laser power. Copyright © 2008 John Wiley & Sons, Ltd.     

EXPERIMENTAL ELECTRON DENSITY ANALYSIS OF MILLERITE

The millerite is of mineral--crystallographic and structure-chemical interest because ofits unusual coordinate number and distances. The experimental electron density distributionof millerite has been determined from high resolution X--ray diffraction data. According tothe distribution of lone pair electrons and their long distances from the nucleus of Ni andS atoms, we suggest that there are multiple coordinate bonding between Ni and S atoms andnormal coordinate bonding between Ni and Ni atoms. These are in reasonable agreement withthe unusual coordinate number, distorted coordinate polyhedron, bonding distances betweenatoms and some metallic properties of millerite.