Semiconductivity in Acceptor‐Doped BaTi _{1− x} Ho _x O _{3− x /2−δ/2}

Acceptor‐doped BaTiO ₃ powders of formula: BaTi _{1− x} Ho _x O _{3− 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 Ho ³⁺ 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 Ti ³⁺ ions; it is suggested that, for these dilute Ho contents, each oxygen vacancy is charge compensated by one Ho ³⁺ and one Ti ³⁺ ion. At higher x , charge compensation is by Ho ³⁺ ions and samples are insulating. A second, more general mechanism to generate Ti ³⁺ ions, and a modest level of semiconductivity, involves reversible oxygen loss at high temperatures.