Defect and adsorbate induced infrared modes in sol–gel derived magnesium oxide nano-crystallites

The chemical route, sol–gel process has emerged as an efficient and cost effective synthesis route for existing and new materials. However, various species can be physisorbed/chemisorbed during the synthesis due to sol–gel route and low processing temperatures. An attempt has therefore been made to study the MgO powder of average crystallite size 3–73.5 nm obtained from sol–gel process by decomposition of dried precursor gel at 500–1000 ∘C in air, oxygen and nitrogen ambient. It has been shown that H2O is both physisorbed and chemisorbed. The chemisorption of H2O has been shown to exhibit formation of hydroxyls at low coordinated sites around 3700 cm−1. Dissociated H+ ions of H2O have also been found adsorbed at five coordinated O2− ions at the surface of MgO giving rise to vibrational modes around 2954 and 2854 cm−1. Further, chemisorption of H2O is shown to exhibit (i) formation of hydrides and (ii) trapping of H−, H+ and H species at F2+, F and F+ defect centres, respectively. Moreover, powder decomposed in nitrogen ambient have shown to exhibit (i) very weak ν (CO) band at ∼2208 cm−1 of Mg2+3c CO adducts and (ii) band at ∼2170 cm−1 of Mg2+4c CO complexes; at 500–600 ∘C.