Semiconductivity in Acceptor-Doped BaTi1−xHoxO3−x/2−δ/2


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Acceptor-doped BaTiO3 powders of formula: BaTi1−xHoxO3−x/2−δ/2: x = 0.0001, 0.001, 0.01, 0.03, and 0.07, were prepared by sol-gel synthesis, fired at 800°C–1500°C and either quenched or slow-cooled to room temperature. Electrical properties of ceramics depended on firing conditions, Ho content, and cooling rate. Pellets of all x values fired at 800°C–1000°C were insulating and, from the presence of OH bands in the IR spectra, charge balance appeared to involve co-doping of Ho3+ and H+ ions without necessity for oxygen vacancy creation. At higher firing temperatures, OH bands were absent. Pellets fired at 1400°C in air and slow cooled were insulating for both low x (0.0001) and high x (0.07) but at intermediate x (0.001 and 0.01) passed through a resistivity minimum of 20–30 Ω cm at room temperature, attributed to the presence of Ti3+ ions; it is suggested that, for these dilute Ho contents, each oxygen vacancy is charge compensated by one Ho3+ and one Ti3+ ion. At higher x, charge compensation is by Ho3+ ions and samples are insulating. A second, more general mechanism to generate Ti3+ ions, and a modest level of semiconductivity, involves reversible oxygen loss at high temperatures.