Calcite Nanocrystals Investigated Using X-ray Absorption Spectroscopy

Abstract

For the present work, calcite nanocrystals were grown by annealing precursors at 500 degrees C. These precursors were obtained by three different thermal schemes. Among these schemes, two involve heating at 100 degrees C for 16 h and 16 + 24 h, respectively. In the third scheme, heating was performed at 100 degrees C for 16 h, followed by annealing at 300 degrees C for 24 h. X-ray diffraction studies, followed by Fourier transform infrared and Raman spectroscopic studies, exhibited the formation of calcite phase of calcium carbonate. Transmission electron microscopy showed that particle sizes of synthesized calcite nanocrystals were in the range of 25-40 nm. Onsets of shape change were also observed with different thermal schemes, using these measurements. X-ray absorption spectroscopy envisaged that the coordination numbers of Ca-O and Ca-Ca shell were not influenced by the thermal schemes; however, bond lengths of these shells were modified. This study in the near edge region evidenced the manifestation of a local electronic structure of calcite when kept in an open environment, depending upon different thermal schemes.