PROCESSING OF LAMINATED BARIUM-TITANATE STRUCTURES FOR STRESS-SENSINGAPPLICATIONS

High-purity, chemically prepared barium titanate was doped with 0.3 at .% lanthanum and, in some cases, counter-doped with 0.04 at.% manganes e 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 b y an insulating BaTiO3, region. The sensor was loaded using a four-poi nt bend test configuration. The change in resistivity with increased l oad was observed to be linear, with positive and negative piezoresisti ve coefficients for the PTCR layers under compression and tension, res pectively. These trends were in general agreement with a stress-depend ent permittivity and the Heywang model of grain-boundary potential bar riers. Piezoresistivity values were derived from the resistivity-stres s slope; these were examined as a function of temperature and sensor g eometry.