Processing of Laminated Barium Titanate Structures for Stress-Sensing Applications

High-purity, chemically prepared barium titanate was doped with 0.3 at.% lanthanum and, in some cases, counterdoped with 0.04 at.% manganese by precipitation. Using standard techniques, tape-cast sheets of the positive temperature coefficient of resistance (PTCR) compositions as well as the base insulating powder were made. A multilayer sensor was laminated and sintered, with upper and lower PTCR regions separated by an insulating BaTiO₃ region. The sensor was loaded using a four-point bend test configuration. The change in resistivity with increased load was observed to be linear, with positive and negative piezo-resistive coefficients for the PTCR layers under compression and tension, respectively. These trends were in general agreement with a stress-dependent permittivity and the Heywang model of grain-boundary potential barriers. Piezoresistivity values were derived from the resistivity-stress slope; these were examined as a function of temperature and sensor geometry.