The influence of the milling liquid on the properties of barium titanate powders and ceramics

Abstract

The influence of the milling liquid on the properties of donor-doped (La ³⁺ ) semiconducting barium titanate (BaTiO ₃ ) ceramics, generated by the mixed oxide technique, was investigated. Distilled water and propan-2-ol were used as milling liquids. Water was found to have two essential effects. First, it dissolves Ba ²⁺ ions out of BaTiO ₃ grains, thus creating core–shell structures which were confirmed by high-resolution electron microscopy (HREM) and electron energy loss spectroscopy (EELS). They consist of a 3–5 nm thick TiO _x -rich layer followed by a layer (ca. 10 nm thick) with a molar Ba/Ti ratio increasing from 0 to 1. These core–shell structures of the BaTiO ₃ powder positively affect the sintering behaviour of the greens by the high reactivity of the Ti-rich interlayer. Secondly, water cleans the BaTiO ₃ powder of acceptor contaminants, producing ceramics with a low electrical resistivity at room temperature. Propan-2-ol-milled ceramics of a comparable composition show an electrical resistivity up to six orders of magnitude higher, owing to the compensation of La ³⁺ -doping by acceptor contaminants.