Kaolinite: Defect defined material properties – A soft X-ray and first principles study of the band gap

• Published in: Journal of electron spectroscopy and related phenomena Vol. 202; pp. 11 - 15
• Main Authors: Pietzsch, A., Nisar, J., Jämstorp, E., Gråsjö, J., Århammar, C., Ahuja, R., Rubensson, J.-E.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-07-2015
• Subjects: Electronic structure; First-principles calculations; Kaolinite; NEXAFS; Spectroscopy; XANES; Spectroscopy; First-principles calculations; Electronic structure; NEXAFS; Kaolinite; XANES
• ISSN: 0368-2048; 1873-2526
• DOI: 10.1016/j.elspec.2015.02.003

•The respective electronic structure of synthetic and natural kaolinite is compared.•The size of the band gap and thus many important material properties are defined by defect states in the band gap.•The oxygen-based defect states are identified and analyzed.•The band gap of kaolinite decreases significantly due to the forming of defects.
By combining X-ray absorption spectroscopy and first principles calculations we have determined the electronic structure of synthetic and natural kaolinite as a model system for engineered and natural clay materials. We have analyzed defect states in the band gap and find that both natural and synthetic kaolinite contain defects where oxygen replaces hydrogen in one of the Al (001)-hydroxyl groups of the kaolinite clay sheets. The band gap of both synthetic and natural kaolinite is found to decrease by about 3.2eV as this defect is formed.