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 BaTiO 3 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.