1. LSQM – Laboratory of Chemical Synthesis of Materials – Department of Materials Engineering, Federal University of Rio Grande do Norte – UFRN, P.O. Box 1524, Natal, RN, Brazil
2. Department of Physics, Federal University of São Carlos – UFSCar, Rod. Washington Luís, km 235 – SP-310 – CEP 13565-905, São Carlos, SP, Brazil