1. School of Physics and Information TechnologyShaanxi Normal University Xi'an P. R. China
2. Department of Chemistry, Faculty of Physical SciencesAhmadu Bello University Zaria Nigeria
3. Department of ChemistryFederal University Gashua Gashua Nigeria
4. Fachgebiet Keramische Werkstoffe/Chair of Advanced Ceramic Materials, Institut für Werkstoffwissenschaften und – technologienTechnische Universität Berlin Berlin Germany