Electrical properties of polycrystalline PTCR barium titanate

Semiconducting n-type barium titanate with a positive temperature coefficient of resistance (PTCR) has been made by doping BaTiO₃ with 0.4 mol% Ho₂O₃. The d.c. resistivity, a.c. resistivity (1.2 kHz) and relative permittivity (1.2 kHz) at different temperatures between room temperature and 523 K have been measured. The high relative permittivity and the PTCR effect are attributed to the existence of potential barriers at the grain boundaries as proposed by Heywang. The height of the potential barrier has been calculated as a function of temperature on the basis of the Heywang model, using the measured resistivity versus temperature and relative permittivity versus temperature above the Curie temperature. Several different kinds of electrode have been used to study the effect of the contact on measurements of resistivity and relative permittivity.