CINÉTICA DE FORMAÇÃO DE NANOCRISTAIS FERROELÉTRICOS EM SISTEMA VÍTREO À BASE DE TeO2

Abstract

TeO2-based glassy materials have been extensively studied and their potentialities require particular attention for the development of new ceramic-glass materials. In this work, viewing the formation of tetragonal BaTiO3 nanocrystals by considering the xBaO–xTiO2–(100–2x)TeO2 (BTT) stoichiometry formula, isothermal treatments were performed under different conditions. Thus, the physical properties of the BTT system were investigated for compositions with x = 7.5, 10.0 and 12.5 mol%, hereafter labeled as 85BTT, 80BTT and 75BTT, respectively. The samples were obtained by the conventional fusion method followed by rapid cooling (known as the quenching method). Particularly, the thermal, structural and optical properties were studied from Differential Thermal Analysis (DTA), X-ray Diffraction (XRD), Raman Spectroscopy and Optical Absorption (OA) analyses. The results showed a strong influence of the BaO-TiO2 concentrations on the studied properties, which could be related to the symmetry breaking of the elemental structural unit (TeO4), due to the TeO4TeO3+1TeO3 structural variation, the covalent character of the TeO bonds, the presence of the lone-pair valence electrons in the TeO2 and, consequently, the formation of non-binding oxygen (NBO's). The UV-Vis cut-off bands revealed the fundamental absorption in the 400-450nm region, where the most polymerized network of the 80BTT samples has provided the highest indirect (Ei = 2.87eV) and direct (Ed = 2.96eV) gap values. The results obtained from XRD and Raman confirmed the presence of the -TeO2 (paratellurite) and -TeO2 (meta-stable) polymorphisms in the structural lattice of the glasses. From the isothermal treatments performed up to 3h, around the initial crystallization temperature (Tx), the hierarchy of the stable paratellurite phase (-TeO2) was confirmed for the 80BTT sample whereas the metastable phase (-TeO2) was confirmed for the 85BTT and 75BTT compositions. In addition, the characteristic reflections of the BaTiO3 (BT) tetragonal ferroelectric phase were identified by XRD (ICSD-073644), revealing the formation of nanocrystals (NCs) with 34nm, 38nm and 42nm average size, with their corresponding vibrational modes identified by Raman spectroscopy. Finally, the results presented in this work show materials with technological potential for nanotechnology applications, such as the role of nanophotonics and the field of optical memories. UNIVERSIDADE ESTADUAL PAULISTA "JÚLIO DE MESQUITA FILHO"FACULDADE DE ENGENHARIA – CAMPUS DE ILHA SOLTEIRA Bolsista do Programa de Incentivo à Qualificação Docente (PIQ/IFGOIANO)