Infrared spectrum of microcrystalline zinc oxide. Electronic and vibrational contributions under different temperature and environmental conditions

The infrared spectrum (700–4000 cm–1) of quasi-stoichiometric microcrystalline ZnO has been recorded at various temperatures (97–523 K) and following various redox treatments.A broad band centred at ca. 1500 cm–1, produced on samples cooled down to 97 K in oxygen, is ascribed to the increasing concentration of un-ionized donor centres.The disappearance of all phonon and surface impurity (OH, carbonate-like species) bands, caused by heating the samples to 433 K both in vacuo and in a hydrogen atmosphere, is ascribed to the phonon–plasmon coupling in microcrystals possessing a rather high concentration of electrons in the conduction band.