Spectroscopic investigations and magnetic measurements on iron-containing barium titanate glass-ceramics

摘要

Glass-ceramics with cubic BaTiO3 as a major and hexagonal BaTi1-xFexO3-delta as a second phase were prepared by crystallization at 560 degrees C in a glass with the composition 20.1Na(2)O/23TiO(2)/23.1BaO/3Al(2)O(3)/7.6B(2)O(3)/17.4SiO(2)/ 5.8Fe(2)O(3). X-ray photoelectron spectroscopy revealed presence of Ti4+ and Fe3+ ions in tetrahedral and octahedral coordination. Ba2+ occurs in different environments depending on the thermal history of the samples. The numbers of bridging and non-bridging oxygens vary with the crystallization time. Electron paramagnetic resonance spectroscopy showed four types of Fe3+ ions that are non-uniformly distributed in the samples: Fe3+ ions in magnetic domains, isolated Fe3+ in a rhombic crystal field, magnetically coupled Fe3+ ions in BaTiO3 and Fe3+ ions located in a crystalline phase. The ratio between the described types of Fe3+ ions depends on the annealing time. Mossbauer spectroscopy detected Fe3+ tetrahedral and octahedral coordinated in the glass. Fe3+ was incorporated in distorted octahedral and pentahedral coordination in the Ti4+ sites of hexagonal BaTiO3 crystals, the electroneutrality being preserved by the occurrence of oxygen vacancies. Vibrating sample magnetometer measurements were used to determine ferromagnetic properties in samples crystallized for times >= 3 h. Maximum magnetization of 0.8 emu/g and a coercive force of 25 Oe were determined for the sample crystallized for 3 h at 560 degrees C.