1. a Department of Physics , Central University of Las Villas , CP 54830 Santa Clara , VC , Cuba
2. b Technology and Machinery Construction Department , Superior Polytechnic Institute , José Antonio Echevarría, Havana , Cuba
3. c Department of Materials Engineering , Catholic University of Rio de Janeiro , Rua Marques de São Vicente 225, Gávea, Rio de Janeiro , RJ , CEP 222541-900, Brazil