Semiconductivity in Acceptor-Doped BaTi_(1-x)Ho_xO_(3_x/2-δ/2)

摘要

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℃-1500℃ 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℃-1000℃ 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℃ 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.