Defect chemistry of the shell region of water-milled BaTiO3 powders

The sintering behaviour of BaTiO3 powders and the resulting microstructure of the corresponding ceramics are controlled by the stoichiometry of the outer region of the grains of the starring powder. These grains exhibit a core-shell structure due to the water attack during powder milling. The hydrolysis results in the formation of lattice-hydroxyl groups. The existence of these processing-related hydroxyl defects is detected by H-1 magic-angle spinning nuclear magnetic resonance (H-1-MAS NMR) as well as differential thermal analysis/thermal gravimetry (DTA/TG) measurements and also verified by electron energy-loss spectroscopy (EELS) in combination with high-resolution transmission electron microscopy (HRTEM). The results are confirmed by detecting the near-edge structure of the O-K edge, the details of which can be interpreted by quantum-mechanical calculations of the electronic density of states in the conduction band. (C) 1998 Elsevier Science S.A. All rights reserved.