Advances in Natural Science: Theory & Applications Volume 3 No. 1 2014, 21-27 ISSN: 1715-7862 (printed version); ISSN: 1715-7870 (online version) url: http://www.ansta.eu doi: http://dx.doi.org/10.12732/ijpam.v3i1.3 P A ansta.eu CRYSTALLIZATION OF BARIUM TITANATE IN OXIDE GLASSES Ruzha Harizanova 1 , Liliya Vladislavova 1 , Aneliya Mazhdrakova 1 , Christian Bocker 2 , Georgi Avdeev 3 , Gichka Tsutsumanova 4 , Ivailo Gugov 1 , Christian R¨ ussel 2 1 Department of Physics, University of Chemical Technology and Metallurgy, 8 Kl. Ohridski Blvd., 1756 Sofia, Bulgaria, e-mail: ruza harizanova@yahoo.com 2 Otto Schott Institute, University of Jena, Fraunhoferstr. 6, 07743 Jena, Germany 3 Institute of Physical Chemistry, Bulgarian Academy of Sciences, Block 11, Acad. G. Bonchev Str., 1113 Sofia, Bulgaria 4 Faculty of Physics, Sofia University, 5 James Bourchier Str, 1164 Sofia, Bulgaria Abstract: The possibility for synthesis of glasses with less than 30 mol% glass- forming oxides is investigated in the systems Na 2 O/BaO/TiO 2 /B 2 O 3 /SiO 2 /Al 2 O 3 and Na 2 O/BaO/TiO 2 /B 2 O 3 /SiO 2 /Al 2 O 3 /Fe 2 O 3 . Bulk glasses are obtained for 5 different Na 2 O/Al 2 O 3 ratios in both systems. The glass-transition and crystallization tempera- tures, determined by DSC, increase with the increasing alumina concentration. Glassy samples from the two systems are annealed above the glass transition temperature. Crystallization of BaTiO 3 for all time-temperature schedules applied is achieved. The resulting microstructure is investigated by scanning electron microscopy and the phase composition is studied by x-ray diffraction. Dependency of the characteristic temper- atures as well as of the crystallite size on the ratio Na 2 O/Al 2 O 3 is observed. The resulting microstructure of samples from both systems is similar as morphology but differs in the mechanism of nucleation and growth of the crystalline phase. It is sug- gested that a phase separation process precedes the crystallization of BaTiO 3 in the system containing Fe 2 O 3 . There is no evidence for unmixing in the system without iron oxide which correlates with the higher stability against crystallization of these glasses. Key Words: barium titanate, crystallization, microstructure, phase separation 1. Introduction Barium titanate, BaTiO 3 is a dielectric material with numerous allotropic modifications [1-4] and many interesting properties among which ferroelectricity, piezoelectricity, optical [1-6] and after appropriate doping semiconducting and even magnetic properties [2]. The two most often preferred modifications of barium titanate are the tetragonal and cubic ones. The tetragonal modification which is ferro- and piezoelectric undergoes phase transition at about 120 o C to the cubic one which is with isotropic dielectric properties [1]. The synthesis temperature of pure BaTiO 3 crystals is very high – of the order of 1600 o C which makes the process of preparation very expensive. Often crystallization from multicomponent oxide glasses with high concentrations of alkali, alkaline earths and 3d-transition metal oxides is used in order to decrease the synthesis temperature of barium titanate [2, 7, 8]. Depending on the composition of the initial glass, ferroelectric nanocrystals with tailored sizes can be prepared using appropriate heat treatment conditions [2, 4]. Different hybrid nanocomposite materials based on BaTiO 3 can be prepared, too [1]. Received: March 11, 2014 c ⃝ 2014 Academic Publications, Ltd. url: www.acadpubl.eu