1. Laboratory
of Carbon and Ceramic Materials, Department of Physics, Federal University of Espírito Santo (UFES), Avenida Fernando Ferrari, 514, 29075-910 Vitória, Espírito Santo, Brazil
2. Federal
Institute of Education, Science and Technology of Espírito Santo, R. Sete de Novembro, 40, 29395-000 Ibatiba, Espírito Santo, Brazil