Positive temperature coefficient in Ho-doped BaTiO3 ceramics

A series of Ho-doped barium titanate ceramics were prepared with dopant con centrations of: 0.03, 0.15, 0.27, 0.4 and 2.0 at.% Ho. DC resistivity measu rements were carried out as a function of temperature from 10 up to 350 deg rees C, The strong (exponential) anomalous increase of the resistivity at t he Curie temperature, T-C approximate to 110 degrees C, was discussed in te rms of Heywang model of positive temperature coefficient (PTC) of resistanc e. The inclusion of Ho has no effect on the room temperature bulk character istics, as the samples were conductive at room temperature. The lowest dopa nt concentration was found to give the steeper resistivity rise at the Curi e temperature and is recommended for practical applications in thermistors. (C) 2000 Elsevier Science Ltd. All rights reserved.