Piezoresistance and Piezocapacitance Effects in Barium Strontium Titanate Ceramics

A large piezoresistance response to hydrostatic pressure is reported for a series of ceramic compositions in the system barium strontium lanthanum titanate (Ba, Sr, La)TiO₂. This property appears to be closely associated with the Curie region (cubic-tetragonal phase transition) and the phenomenon of a positive temperature coefficient of resistance for these same compositions. The piezoresistance coefficient, similar to the temperature coefficient of resistance, is positive in the Curie region, and is found to range up to the order of 700 X 10 ⁻¹² sq. cm. per dyne. Consistent with the observed piezoresistance effect, a positive piezocapacitive effect, ranging up to the order of 700 x 10⁻¹² sq. cm. per dyne, is observed in these compositions in the absence of the lanthanum impurity which produces semiconduction. It is suggested that these materials may be of interest in pressure-sensitive devices such as acoustic transducers and pressure-sensing elements and in techniques for measuring force and displacement.